Highly Luminescent, Size- and Shape-Tunable Copper Indium Selenide Based Colloidal Nanocrystals

Structural Ordering in Ultrasmall Multicomponent Chalcogenides: The Case of Quaternary Cu-Zn-In-Se Nanocrystals

The compositional tunability of non-isovalent multicomponent chalcogenide thin films and the extent of atomic ordering of their crystal structure is key to the performance of many modern technologies. In contrast, the effects of ordering are rarely studied for quantum-confined materials, such as colloidal nanocrystals. In this paper, the possibilities around composition tunability and atomic ordering are explored in ultrasmall ternary and quaternary quantum dots, taking I-III-VI-group Cu-Zn-In-Se semiconductor as a case study. A quantitative synthesis for 3.3 nm quaternary chalcogenide nanocrystals is developed and shown that cation and cationic vacancy ordering can be achieved in these systems consisting of only 100s of atoms. Combining experiment and theoretical calculations, the relationship between structural ordering and optical properties of the materials are demonstrated. It is found that the arrangement and ordering of cationic sublattice plays an important role in the luminescent efficiency. Specifically, the concentration of Cu-vacancy couples in the nanocrystal correlates with luminescence quantum yield, while structure ordering increases the occurrence of such optically active Cu-vacancy units. On the flip side, the detrimental impact of cationic site disorder in I-III-VI nanocrystals can be mitigated by introducing a cation of intermediate valence, such as Zn (II).

Multishell Silver Indium Selenide-Based Quantum Dots and Their Poly(methyl methacrylate) Composites for Application in Red-Light-Emitting Diodes

In this work, the production of novel multishell silver indium selenide quantum dots (QDs) shelled with zinc selenide and zinc sulfide through a multistep synthesis precisely designed to develop high-quality red-emitting QDs is explored. The formation of the multishell nanoheterostructure significantly improves the photoluminescence quantum yield of the nanocrystals from 3% observed for the silver indium selenide core to 27 and 46% after the deposition of the zinc selenide and zinc sulfide layers, respectively. Moreover, the incorporation of the multishelled QDs in a poly(methyl methacrylate) (PMMA) matrix via in situ radical polymerization is investigated, and the role of thiol ligand passivation is proven to be fundamental for the stabilization of the QDs during the polymerization step, preventing their decomposition and the relative luminescence quenching. In particular, the role of interface chemistry is investigated by considering both surface passivation by inorganic zinc chalcogenide layers, which allows us to improve the optical properties, and organic thiol ligand passivation, which is fundamental to ensuring the chemical stability of the nanocrystals during in situ radical polymerization. In this way, it is possible to produce silver-indium selenide QD-PMMA composites that exhibit bright red luminescence and high transparency, making them promising for potential applications in photonics. Finally, it is demonstrated that the new silver indium selenide QD-PMMA composites can serve as an efficient color conversion layer for the production of red light-emitting diodes.

Near-Infrared Nanophosphors Based on CuInSe2 Quantum Dots with Near-Unity Photoluminescence Quantum Yield for Micro-LEDs Applications

Highly efficient near-infrared (NIR) luminescent nanomaterials are urgently required for portable mini or micro phosphors-converted light-emitting diodes (pc-LEDs). However, most existing NIR-emitting phosphors are generally restricted by their low photoluminescence (PL) quantum yield (QY) or large particle size. Herein, a kind of highly efficient NIR nanophosphors is developed based on copper indium selenide quantum dots (CISe QDs). The PL peak of these QDs can be exquisitely manipulated from 750 to 1150 nm by altering the stoichiometry of Cu/In and doping with Zn2+ . Their absolute PLQY can be significantly improved from 28.6% to 92.8% via coating a ZnSe shell. By combining the phosphors with a commercial blue chip, an NIR pc-LED is fabricated with remarkable photostability and a record-high radiant flux of 88.7 mW@350 mA among the Pb/Cd-free QDs-based NIR pc-LEDs. Particularly, such QDs-based nanophosphors acted as excellent luminescence converter for NIR micro-LEDs with microarray diameters below 5 µm, which significantly exceeds the resolutions of current commercial inkjet display pixels. The findings may open new avenues for the exploration of highly efficient NIR micro-LEDs in a variety of applications.

Luminescent Quantum Dots: Synthesis, Optical Properties, Bioimaging and Toxicity

Luminescent nanomaterials such as semiconductor nanocrystals (NCs) and quantum dots (QDs) attract much attention to optical detectors, LEDs, photovoltaics, displays, biosensing, and bioimaging. These materials include metal chalcogenide QDs and metal halide perovskite NCs. Since the introduction of cadmium chalcogenide QDs to biolabeling and bioimaging, various metal nanoparticles (NPs), atomically precise metal nanoclusters, carbon QDs, graphene QDs, silicon QDs, and other chalcogenide QDs have been infiltrating the nano-bio interface as imaging and therapeutic agents. Nanobioconjugates prepared from luminescent QDs form a new class of imaging probes for cellular and in vivo imaging with single-molecule, super-resolution, and 3D resolutions. Surface modified and bioconjugated core-only and core-shell QDs of metal chalcogenides (MX; M = Cd/Pb/Hg/Ag, and X = S/Se/Te,), binary metal chalcogenides (MInX₂; M = Cu/Ag, and X = S/Se/Te), indium compounds (InAs and InP), metal NPs (Ag, Au, and Pt), pure or mixed precision nanoclusters (Ag, Au, Pt), carbon nanomaterials (graphene QDs, graphene nanosheets, carbon NPs, and nanodiamond), silica NPs, silicon QDs, etc. have become prevalent in biosensing, bioimaging, and phototherapy. While heavy metal-based QDs are limited to in vitro bioanalysis or clinical testing due to their potential metal ion-induced toxicity, carbon (nanodiamond and graphene) and silicon QDs, gold and silica nanoparticles, and metal nanoclusters continue their in vivo voyage towards clinical imaging and therapeutic applications. This review summarizes the synthesis, chemical modifications, optical properties, and bioimaging applications of semiconductor QDs with particular references to metal chalcogenide QDs and bimetallic chalcogenide QDs. Also, this review highlights the toxicity and pharmacokinetics of QD bioconjugates.

Thermally Activated Delayed Near-Infrared Photoluminescence from Functionalized Lead-Free Nanocrystals

As an analogue to thermally activated delayed fluorescence (TADF) of organic molecules, thermally activated delayed photoluminescence (TADPL) observed in molecule-functionalized semiconductor nanocrystals represents an exotic mechanism to harvest energy from dark molecular triplets and to obtain controllable, long-lived PL from nanocrystals. The reported TADPL systems have successfully covered the visible spectrum. However, TADF molecules already emit very efficiently in the visible, diminishing the technological impact of the less-efficient nanocrystal-molecule TADPL. Here we report bright, near-infrared TADPL in lead-free CuInSe₂ nanocrystals functionalized with carboxylated tetracene ligands, which results from efficient triplet energy transfer from photoexcited nanocrystals to ligands, followed with thermally activated reverse energy transfer from ligand triplets back to nanocrystals. This strategy prolonged the nanocrystal exciton lifetime from 100 ns to 60 μs at room temperature.

Narrow-Bandwidth Blue-Emitting Ag-Ga-Zn-S Semiconductor Nanocrystals for Quantum-Dot Light-Emitting Diodes

I-III-VI type semiconductor nanocrystals (NCs) have attracted considerable attention in the display field. Herein, we realized the synthesis of narrow-bandwidth blue-emitting Ag-Ga-Zn-S (AGZS) NCs via a facile one-pot method. Intriguingly, the Ag/Zn feeding ratio and Ag/Ga feeding ratio are crucial for the realization of narrow-bandwidth AGZS NCs. By choosing a Ag/Zn feeding ratio of 4:1 and Ag/Ga feeding ratio of 1:8, AGZS NCs demonstrate a typical blue emission at 470 nm with a narrow full width at half-maximum (fwhm) of 48 nm, which is mainly generated from the band-to-hole recombination rather than the donor-acceptor pair (DAP) recombination. Furthermore, a solution-processed quantum-dot light-emitting device based on AGZS NCs exhibits a narrow electroluminescent bandwidth of 53 nm and high luminance over 123.1 cd m^-2, as well as a high external quantum efficiency (EQE) of 0.40%. Our work highlights AGZS NCs with high color purity as an important candidate for blue-light-emitting devices.

Phonon Raman spectroscopy of nanocrystalline multinary chalcogenides as a probe of complex lattice structures

Ternary (I-III-VI) and quaternary (I-II-IV-VI) metal-chalcogenides like CuInS₂or Cu₂ZnSn(S,Se)₄are among the materials currently most intensively investigated for various applications in the area of alternative energy conversion and light-emitting devices. They promise more sustainable and affordable solutions to numerous applications, compared to more developed and well understood II-VI and III-V semiconductors. Potentially superior properties are based on an unprecedented tolerance of these compounds to non-stoichiometric compositions and polymorphism. However, if not properly controlled, these merits lead to undesirable coexistence of different compounds in a single polycrystalline lattice and huge concentrations of point defects, becoming an immense hurdle on the way toward real-life applications. Raman spectroscopy of phonons has become one of the most powerful tools of structural diagnostics and probing physical properties of bulk and microcrystalline I-III-VI and I-II-IV-VI compounds. The recent explosive growth of the number of reports on fabrication and characterization of nanostructures of these compounds must be pointed out as well as the steady use of Raman spectroscopy for their characterization. Interpretation of the vibrational spectra of these compound nanocrystals (NCs) and conclusions about their structure can be complicated compared to bulk counterparts because of size and surface effects as well as emergence of new structural polymorphs that are not realizable in the bulk. This review attempts to summarize the present knowledge in the field of I-III-VI and I-II-IV-VI NCs regarding their phonon spectra and capabilities of Raman and IR spectroscopies in the structural characterizations of these promising families of compounds.

Review of Mn-Doped Semiconductor Nanocrystals for Time-Resolved Luminescence Biosensing/Imaging

Colloidal semiconductor nanocrystals (NCs) have been developed for decades and are widely applied in biosensing/imaging. However, their biosensing/imaging applications are mainly based on luminescence-intensity measurement, which suffers from autofluorescence in complex biological samples and thus limits the biosensing/imaging sensitivities. It is expected for these NCs to be further developed to gain luminescence features that can overcome sample autofluorescence. On the other hand, time-resolved luminescence measurement utilizing long-lived-luminescence probes is an efficient technique to eliminate short-lived autofluorescence of samples while recording time-resolved luminescence of the probes for signal measurement after pulsed excitation from a light source. Despite time-resolved measurement being very sensitive, the optical limitations of many of the current long-lived-luminescence probes cause time-resolved measurement to be generally performed in laboratories with bulky and costly instruments. In order to apply highly sensitive time-resolved measurement for in-field or point-of-care (POC) testing, it is essential to develop probes possessing high brightness, low-energy (visible-light) excitation, and long lifetimes of up to milliseconds. Such desired optical features can significantly simplify the design criteria of time-resolved measurement instruments and facilitate the development of low-cost, compact, sensitive instruments for in-field or POC testing. Mn-doped NCs have recently been in rapid development and provide a strategy to solve the challenges faced by both colloidal semiconductor NCs and time-resolved luminescence measurement. In this review, we outline the major achievements in the development of Mn-doped binary and multinary NCs, with emphasis on their synthesis approaches and luminescence mechanisms. Specifically, we demonstrate how researchers approached these obstacles to achieve the aforementioned desired optical properties on the basis of the progressive understanding of Mn emission mechanisms. Afterward, we review representative applications of Mn-doped NCs in time-resolved luminescence biosensing/imaging and present the potential of Mn-doped NCs in advancing time-resolved luminescence biosensing/imaging for in-field or POC testing.

Highly efficient near-infrared light-emitting diodes based on Zn:CuInSe2/ZnS//ZnS quantum dots with double shell engineering

Near-infrared (NIR) quantum dot-based light-emitting diodes (QLEDs) developed rapidly in the fields of biomedical applications, telecommunications, sensing and diagnostics. However, it remains an enormous challenge for the synthesis of high-quality NIR QD materials with low toxicity or non-toxicity, high photoluminescence (PL) quantum yields (QYs) and high stability. Herein, we used a facile method to synthesize large-sized (8 nm) and thick-shell NIR Zn:CuInSe₂/ZnS//ZnS QDs by engineering a double ZnS shell. The resulting NIR QDs exhibited high PL QYs of 80%, and excellent photochemical stability, which could be ascribed to the decreased lattice mismatch of the core/shell interface by the introduced Zn element into CuInSe₂ cores and the energetic defect passivation of the double ZnS shell engineering. Furthermore, the high-quality Zn:CuInSe₂/ZnS//ZnS QDs based LEDs exhibited the maximum external quantum efficiency (EQE) of 3.0%, 4.0% and 2.5% for PL peaks located at 705, 719 and 728 nm, respectively. This efficiency is comparable to that of the outstanding PbS- and InAs-based NIR QLEDs, as well as the avoidance of toxic heavymetal and/or hazardous reagents in this work. The synthesized high-quality Zn:CuInSe₂/ZnS//ZnS QDs could be expected to promote the potential applications of heavy-metal-free QDs in the NIR fields.

Bright, Magnetic NIR-II Quantum Dot Probe for Sensitive Dual-Modality Imaging and Intensive Combination Therapy of Cancer

Improving the effectiveness of cancer therapy will require tools that enable more specific cancer targeting and improved tumor visualization. Theranostics have the potential for improving cancer care because of their ability to serve as both diagnostics and therapeutics; however, their diagnostic potential is often limited by tissue-associated light absorption and scattering. Herein, we develop CuInSe₂@ZnS:Mn quantum dots (QDs) with intrinsic multifunctionality that both enable the accurate localization of small metastases and act as potent tumor ablation agents. By leveraging the growth kinetics of a ZnS shell on a biocompatible CuInSe₂ core, Mn doping, and folic acid functionalization, we produce biocompatible QDs with high near-infrared (NIR)-II fluorescence efficiency up to 31.2%, high contrast on magnetic resonance imaging (MRI), and preferential distribution in 4T1 breast cancer tumors. MRI-enabled contrast of these nanoprobes is sufficient to timely identify small metastases in the lungs, which is critically important for preventing cancer spreading and recurrence. Further, exciting tumor-resident QDs with NIR light produces both fluorescence for tumor visualization through radiative recombination pathways as well as heat and radicals through nonradiative recombination pathways that kill cancer cells and initiate an anticancer immune response, which eliminates tumor and prevents tumor regrowth in 80% of mice.

Optical Properties of Mn-Doped CuGa(In)S-ZnS Nanocrystals (NCs): Effects of Host NC and Mn Concentration

Time-gated fluorescence measurement (TGFM) using long-life fluorescence probes is a highly sensitive fluorescence-measurement technology due to the inherently high signal-to-background ratio. Although many probes for TGFM such as luminescent-metal-complex probes and lanthanide-doped nanoparticles are in development, they generally need sophisticated/expensive instruments for biosensing/imaging applications. Probes possessing high brightness, low-energy (visible light) excitation, and long lifetimes up to milliseconds of luminescence, are highly desired in order to simplify the optical and electronic design of time-gated instruments (e.g., adopting non-UV-grade optics or low-speed electronics), lower the instrument complexity and cost, and facilitate broader applications of TGFM. In this work, we developed Mn-doped CuGa(In)S-ZnS nanocrystals (NCs) using simple and standard synthetic steps to achieve all the desired optical features in order to investigate how the optical properties (fluorescence/absorption spectra, brightness, and lifetimes) of the Mn-doped NCs are affected by different host NCs and Mn concentrations in host NCs. With optimal synthetic conditions, a library of Mn-doped NCs was achieved that possessed high brightness (up to 47% quantum yield), low-energy excitation (by 405 nm visible light), and long lifetimes (up to 3.67 ms). Additionally, the time-domain fluorescence characteristics of optimal Mn-doped NCs were measured under pulsed 405 nm laser excitation and bandpass-filter-based emission collection. The measurement results indicate the feasibility of these optimal Mn-doped NCs in TGFM-based biosensing/imaging.

Synthetic Ligand Selection Affects Stoichiometry, Carrier Dynamics, and Trapping in CuInSe2 Nanocrystals

CuInSe₂ nanocrystals exhibit tunable near-infrared bandgaps that bolster utility in photovoltaic applications as well as offer potential as substitutes for more toxic Cd- and Pb-based semiconductor compositions. However, they can present a variety of defect states and unusual photophysics. Here, we examine the effects of ligand composition (oleylamine, diphenylphosphine, and tributylphosphine) on carrier dynamics in these materials. Via spectroscopic measurements such as photoluminescence and transient absorption, we find that ligands present during the synthesis of CuInSe₂ nanocrystals impart nonradiative electronic states which compete with radiative recombination and give rise to low photoluminescence quantum yields. We characterize the nature of these defect states (hole vs electron traps) and investigate whether they exist at the surface or interior of the nanocrystals. Carrier lifetimes are highly dependent on ligand identity where oleylamine-capped nanocrystals exhibit rapid trapping (<20 ps) followed by diphenylphosphine (<500 ps) and finally tributylphosphine (>2 ns). A majority of carrier population localizes at indium copper antisites (electrons), copper vacancies (holes), or surface traps (electrons and/or holes), all of which are nonemissive.

Synthesis and Optical Properties of In2S3-Hosted Colloidal Zn-Cu-In-S Nanoplatelets

High-efficiency photoluminescence quaternary hexagon Zn-Cu-In-S (ZCIS) nanoplatelets (NPls) have been synthesized by a two-step cation exchange method, which starts with the In₂S₃ NPls followed by the addition of Cu and Zn. It is the first time that In₂S₃ NPls are used as templates to synthesize ZCIS NPls. In this paper, the reaction temperature of In₂S₃ is essential for the formation of NPls. The photoluminescence wavelength of NPls can be tuned by adjusting the temperature of Cu addition. To enhance the stability of the resulting NPls and to improve their optical properties, we introduced Zn²⁺ and obtained ZCIS NPls by cation exchange on the surface. It is worth noting that the obtained ZCIS NPls show a shorter fluorescence lifetime than other ternary copper sulfide-based NPls. This work provides a new way to synthesize high-efficiency, nontoxic, and no byproduct ZCIS NPls.

Olivine Crystal Structure-Directed Twinning in Iron Germanium Sulfide (Fe2GeS4) Nanoparticles

Understanding the microstructure of complex crystal structures is critical for controlling material properties in next-generation devices. Synthetic reports of twinning in bulk and nanostructured crystals with detailed crystallographic characterization are integral for advancing systematic studies of twinning phenomena. Herein, we report a synthetic route to controllably twinned olivine nanoparticles. Microstructural characterization of Fe₂GeS₄ nanoparticles via electron microscopy (imaging, diffraction, and crystallographic analysis) demonstrates the formation of triplets of twins, or trillings. We establish synthetic control over the particle crystallinity and crystal growth. We describe the geometrical basis for twin formation, hexagonal pseudosymmetry of the orthorhombic lattice, and rank all of the reported olivine compounds according to this favorability to form twins. The work in this study highlights an area ripe for future exploration with respect to the advancement of solution-phase synthetic approaches that can control microstructure in compositionally complex, technologically relevant structures. Finally, we discuss the potential implications for olivine properties and performance in various applications.

Near-infrared emitting Cu-In-Se/ZnS core/shell quantum dots: aqueous synthesis and sulfur source effects

The present study reports an aqueous synthesis approach towards Cu-In-Se/ZnS quantum dots with emission in the near-infrared spectral range. The photoluminescence of the dots can be effectively controlled by adjusting the sulfur source, to achieve increased quantum yields (four times higher) and red-shifted emission peaks (from 809 nm to 830 nm).

Synthesis of deep red emitting Cu-In-Zn-Se/ZnSe quantum dots for dual-modal fluorescence and photoacoustic imaging

CuInSe₂ quantum dots (QDs) are one of the most important Cd-free fluorescent probes; they usually exhibited low fluorescence intensity, suggesting that a considerable amount of absorbed photon energy was lost as heat. In this study we aimed to improve the fluorescence intensity of CuInSe₂ QDs and investigate their photoacoustic (PA) signal resulting from the heat dissipation, which was previously rarely reported. Cu-In-Zn-Se/ZnSe QDs were synthesized by adopting two strategies of Zn doping and ZnSe shell growth. It was found that there was an upper limit for Zn concentration beyond which the fluorescence intensity began to decrease. In addition, a blue shift of the emission peak of Cu-In-Zn-Se/ZnSe QDs was observed at high concentrations of ZnSe precursor due to the diffusion of excessive Zn. To prepare the dual-modal fluorescence and PA imaging probe, poly(maleic anhydride-alt-1-octadecene) (PMAO) modified with polyethylene glycol (PEG) was coated on the QDs, which led to a slight reduction in fluorescence. Cellular labeling on HeLa cells was performed to demonstrate the utility of these probes for fluorescence imaging. We further studied the in vitro PA imaging capabilities of the Cu-In-Zn-Se/ZnSe/PMAO-g-PEG nanoparticles, which showed a distinct PA signal beyond 1.0 mg ml^-1. The current work demonstrated that a moderate amount of Zn doping is necessary for enhancing fluorescence and there is a limit beyond which the fluorescence will be diminished. We also demonstrated the proof of concept that Cu-In-Zn-Se/ZnSe QDs are able to serve as a potential PA imaging contrast agent.

SDS-Stabilized CuInSe2/ZnS Multinanocomposites Prepared by Mechanochemical Synthesis for Advanced Biomedical Application

The CuInSe2/ZnS multiparticulate nanocomposites were first synthesized employing two-step mechanochemical synthesis. In the first step, tetragonal CuInSe2 crystals prepared from copper, indium and selenium precursors were co-milled with zinc acetate dihydrate and sodium sulfide nonahydrate as precursors for ZnS in different molar ratios by mechanochemical route in a planetary mill. In the second step, the prepared CuInSe2/ZnS nanocrystals were further milled in a circulation mill in sodium dodecyl sulphate (SDS) solution (0.5 wt.%) to stabilize the synthesized nanoparticles. The sodium dodecyl sulphate capped CuInSe2/ZnS 5:0-SDS nanosuspension was shown to be stable for 20 weeks, whereas the CuInSe2/ZnS 4:1-SDS one was stable for about 11 weeks. After sodium dodecyl sulphate capping, unimodal particle size distribution was obtained with particle size medians approaching, respectively, 123 nm and 188 nm for CuInSe2/ZnS 5:0-SDS and CuInSe2/ZnS 4:1-SDS nanocomposites. Successful stabilization of the prepared nanosuspensions due to sodium dodecyl sulphate covering the surface of the nanocomposite particles was confirmed by zeta potential measurements. The prepared CuInSe2/ZnS 5:0-SDS and CuInSe2/ZnS 4:1-SDS nanosuspensions possessed anti-myeloma sensitizing potential assessed by significantly reduced viability of multiple myeloma cell lines, with efficient fluorescence inside viable cells and higher cytotoxic efficacy in CuInSe2/ZnS 4:1-SDS nanosuspension.

Manipulating Electronic Structure from the Bottom-Up: Colloidal Nanocrystal-Based Semiconductors

Semiconductors assembled from colloidal nanocrystals (NCs) are often described in the same terms as their single-crystalline counterparts with references to conduction and valence band edges, doping densities, and electronic defects; however, how and why semiconductor properties manifest in these bottom-up fabricated thin films can be fundamentally different. In this Perspective, we describe the factors that determine the electronic structure in colloidal NC-based semiconductors, and comment on approaches for measuring or calculating this electronic structure. Finally, we discuss future directions for these semiconductors and highlight their potential to bridge the divide between localized quantum effects and long-range transport in thin films.

Phase-Controlled Growth of CuInS2 Shells to Realize Colloidal CuInSe2/CuInS2 Core/Shell Nanostructures

Synthetic routes to deposit CuInS₂ (CIS) shells with either a cubic chalcopyrite (CP) or a hexagonal wurtzite (WZ) phase on trigonal pyramidal-shaped CuInSe₂ (CISe) core nanocrystals (NCs) with a cubic CP crystal structure have been developed and governed by tuning the amount of the sulfur precursor tert-dodecanethiol. During the synthesis of CP-CIS/CP-CISe core/shell NCs, the CP-CIS shell initially starts to grow epitaxially in a uniform way, while the further addition of the CIS precursor induces islandlike growth, and finally a branched CIS shell is formed. In a stark contrast, when a WZ-CIS shell is deposited, it initially grows on a portion of each of the facets of the trigonal pyramidal-shaped CISe cores to form a monolayer, which then continues to increase in thickness and forms a multilayered WZ-CIS shell. Both CP-CISe/CP-CIS core/shell NCs and CP-CISe/WZ-CISe core/shell NCs exhibit rather low photoluminescence quantum yields (<10%), even with a smaller-sized CISe core, which calls for further refinements of the shell growth methods. Synthetic methods for the growth of CIS shells as described here allow for direct deposition of cadmium-free ternary compounds as shell materials and provide important insights into the different modes of growth of heterostructured NCs, ranging from epitaxial to island- and branched-like, as well to the facet-specific multilayer deposition.

Amide-Assisted Synthesis of Iron Germanium Sulfide (Fe2GeS4) Nanostars: The Effect of LiN(SiMe3)2 on Precursor Reactivity for Favoring Nanoparticle Nucleation or Growth

Olivine Fe₂GeS₄ has been identified as a promising photovoltaic absorber material introduced as an alternate candidate to iron pyrite, FeS₂. The compounds share similar benefits in terms of elemental abundance and relative nontoxicity, but Fe₂GeS₄ was predicted to have higher stability with respect to decomposition to alternate phases and, therefore, more optimal device performance. Our initial report of the nanoparticle (NP) synthesis for Fe₂GeS₄ was not well understood and required an inefficient 24 h growth to dissolve an iron sulfide impurity. Here, we report an amide-assisted Fe₂GeS₄ NP synthesis that directly forms the phase-pure product in minutes. This significant advance was achieved by the replacement of the poorly understood hexamethyldisilazane (HMDS) additive and TMS₂S by the conjugate base, lithium bis(trimethylsilyl)amide (LiN(SiMe₃)₂), and elemental S, respectively. We hypothesized that fragments of both TMS₂S and HMDS had carried out the roles that Brønsted bases play in amide-assisted NP syntheses and were necessary for Ge incorporation. Convolution of this role with the supply of S in TMS₂S caused the iron sulfide impurities. Separating these effects in the use of LiN(SiMe₃)₂ and elemental S resulted in synthetic control over the ternary phase. Herein we explore the Fe-Ge-S reaction landscape and the role of the base. Its concentration was found to increase the reactivities of the Fe, Ge, and S precursors, and we discuss possible metal-amide intermediates. This affords tunability in two areas: favorability of NP nucleation versus growth and phase formation. The phase-purity of Fe₂GeS₄ depends on the molar ratios of the cations, base, and amine as well as the Fe:Ge:S molar ratios. The resultant Fe₂GeS₄ NPs exhibit an interesting star anise-like morphology with stacks of nanoplates that intersect along a 6-fold rotation axis. The optical properties of the Fe₂GeS₄ NPs are consistent with previously published measurements showing a measured band gap of 1.48 eV.

Spectroscopic and Magneto-Optical Signatures of Cu1+ and Cu2+ Defects in Copper Indium Sulfide Quantum Dots

Colloidal quantum dots (QDs) of I-III-VI ternary compounds such as copper indium sulfide (CIS) and copper indium selenide (CISe) have been under intense investigation due to both their unusual photophysical properties and considerable technological utility. These materials feature a toxic-element-free composition, a tunable bandgap that covers near-infrared and visible spectral energies, and a highly efficient photoluminescence (PL) whose spectrum is located in the reabsorption-free intragap region. These properties make them attractive for light-emission and light-harvesting applications including photovoltaics and luminescent solar concentrators. Despite a large body of literature on device-related studies of CISe(S) QDs, the understanding of their fundamental photophysical properties is surprisingly poor. Two particular subjects that are still heavily debated in the literature include the mechanism(s) for strong intragap emission and the reason(s) for a poorly defined (featureless) absorption edge, which often "tails" below the nominal bandgap. Here, we address these questions by conducting comprehensive spectroscopic studies of CIS QD samples with varied Cu-to-In ratios using resonant PL and PL excitation, femtosecond transient absorption, and magnetic circular dichroism measurements. These studies reveal a strong effect of stoichiometry on the concentration of Cu¹⁺ vs Cu²⁺ defects (occurring as Cu_In^″ and Cu_Cu^• species, respectively), and their effects on QD optical properties. In particular, we demonstrate that the increase in the relative amount of Cu²⁺ vs Cu¹⁺ centers suppresses intragap absorption associated with Cu¹⁺ states and sharpens band-edge absorption. In addition, we show that both Cu¹⁺ and Cu²⁺ centers are emissive but are characterized by distinct activation mechanisms and slightly different emission energies due to different crystal lattice environments. An important overall conclusion of this study is that the relative importance of the Cu²⁺ vs Cu¹⁺ emission/absorption channels can be controlled by tuning the Cu-to-In ratio, suggesting that the control of sample stoichiometry represents a powerful tool for achieving functionalities (e.g., strong intragap emission) that are not accessible with ideal, defect-free materials.

Influence of a bifunctional linker on the loading of Cu2AgInS4 QDs onto porous TiO2 NFs to use as an efficient photoanode to boost the photoconversion efficiency of QDSCs

Quaternary Cu₂AgInS₄ quantum dots anchored more onto porous TiO₂ NFs through a linker, 3-mercaptopropionic acid exhibits higher photoconversion efficiency of QDSC than that of the same anchored without a linker.

Triplet Sensitization by "Self-Trapped" Excitons of Nontoxic CuInS2 Nanocrystals for Efficient Photon Upconversion

Triplet energy transfer (TET) from semiconductor nanocrystals (NCs) has recently emerged as a new triplet sensitization paradigm. It remains unclear how trap states pervasive in NCs influence TET or whether trapped excitons can undergo efficient TET. Here we partially address this issue by studying TET from CuInS₂ NCs as a model system because their photogenerated excitons are known to be "self-trapped" due to hole localization to intragap Cu states. We found that, thanks to the long lifetime (209 ± 17 ns) of self-trapped excitons, they could be extracted with an efficiency of ∼92.3% by surface-anchored anthracene despite that the TET rate was relatively slow (57.1 ± 1.7 μs^-1). We further leveraged this efficient sensitization to achieve triplet-triplet-annihilation photon upconversion (TTA-UC) with a quantum yield of 18.6 ± 0.3%. Thus, this study not only demonstrates trapped excitons can undergo efficient TET as well, but also presents the first TTA-UC system sensitized by nontoxic NCs which is important for the real-life application of this technique.

Eco-Friendly Colloidal Quantum Dot-Based Luminescent Solar Concentrators

Luminescent solar concentrators (LSCs) have attracted significant attention as promising solar energy conversion devices for building integrated photovoltaic (PV) systems due to their simple architecture and cost-effective fabrication. Conventional LSCs are generally comprised of an optical waveguide slab with embedded emissive species and coupled PV cells. Colloidal semiconductor quantum dots (QDs) have been demonstrated as efficient emissive species for high-performance LSCs because of their outstanding optical properties including tunable absorption and emission spectra covering the ultraviolet/visible to near-infrared region, high photoluminescence quantum yield, large absorption cross sections, and considerable photostability. However, current commonly used QDs for high-performance LSCs consist of highly toxic heavy metals (i.e., cadmium and lead), which are fatal to human health and the environment. In this regard, it is highly desired that heavy metal-free and environmentally friendly QD-based LSCs are comprehensively studied. Here, notable advances and developments of LSCs based on unary, binary, and ternary eco-friendly QDs are presented. The synthetic approaches, optical properties of these eco-friendly QDs, and consequent device performance of QD-based LSCs are discussed in detail. A brief outlook pointing out the existing challenges and prospective developments of eco-friendly QD-based LSCs is provided, offering guidelines for future device optimizations and commercialization.

Visual Appearance of Nanocrystal-Based Luminescent Solar Concentrators

The luminescent solar concentrator (LSC) is a promising concept for the integration of photovoltaic (PV) generators into the building envelope. Having the form of semitransparent plates, LSCs offer a high degree of flexibility and can be used as windows or facades, as part of the of building-integrated photovoltaic (BIPV) industry. Existing performance characterizations of LSC devices focus almost exclusively on electric power generation. However, when used as window components, the transmitted spectrum can alter the color, potentially affecting the visual comfort of the occupants by altering the properties of the sunlight. In this study, eight different state-of-the-art nanocrystals are evaluated as potential candidates for LSC window luminophores, using Monte Carlo simulations. The transparency of each LSC window varies between 90% and 50%, and the color-rendering properties are assessed with respect to the color rendering index (CRI) and the correlated color temperature (CCT). It is found that luminophores with a wide absorption bandwidth in the visible spectrum can maintain a high CRI value (above 85) and CCT values close to the Planckian locus, even for high luminophore concentrations. In contrast, luminophores that only absorb partly in the visible spectrum suffer from color distortion, a situation characterized by low CCT and CRI values, even at high transmittance.

Colloidal Phase-Change Materials: Synthesis of Monodisperse GeTe Nanoparticles and Quantification of Their Size-Dependent Crystallization

Phase-change memory materials refer to a class of materials that can exist in amorphous and crystalline phases with distinctly different electrical or optical properties, as well as exhibit outstanding crystallization kinetics and optimal phase transition temperatures. This paper focuses on the potential of colloids as phase-change memory materials. We report a novel synthesis for amorphous GeTe nanoparticles based on an amide-promoted approach that enables accurate size control of GeTe nanoparticles between 4 and 9 nm, narrow size distributions down to 9-10%, and synthesis upscaling to reach multigram chemical yields per batch. We then quantify the crystallization phase transition for GeTe nanoparticles, employing high-temperature X-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. We show that GeTe nanoparticles crystallize at higher temperatures than the bulk GeTe material and that crystallization temperature increases with decreasing size. We can explain this size-dependence using the entropy of crystallization model and classical nucleation theory. The size-dependences quantified here highlight possible benefits of nanoparticles for phase-change memory applications.

Colloidal Phase-Change Materials: Synthesis of Monodisperse GeTe Nanoparticles and Quantification of Their Size-Dependent Crystallization

Phase-change memory materials refer to a class of materials that can exist in amorphous and crystalline phases with distinctly different electrical or optical properties, as well as exhibit outstanding crystallization kinetics and optimal phase transition temperatures. This paper focuses on the potential of colloids as phase-change memory materials. We report a novel synthesis for amorphous GeTe nanoparticles based on an amide-promoted approach that enables accurate size control of GeTe nanoparticles between 4 and 9 nm, narrow size distributions down to 9-10%, and synthesis upscaling to reach multigram chemical yields per batch. We then quantify the crystallization phase transition for GeTe nanoparticles, employing high-temperature X-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. We show that GeTe nanoparticles crystallize at higher temperatures than the bulk GeTe material and that crystallization temperature increases with decreasing size. We can explain this size-dependence using the entropy of crystallization model and classical nucleation theory. The size-dependences quantified here highlight possible benefits of nanoparticles for phase-change memory applications.

Transformation of Indium and Gallium Metal into Mixed Group 11/13 Ternary Sulfide Nanoparticles by Using a Dithioic Acid

Heterobimetallic Group 11/13 sulfide nanoparticles (AgInS₂ , CuInS₂ , Ag₉ GaS₆ , and CuGaS₂ ) are formed by treatment of [M(S₂ CAr)₃ ] (M=Ga or In) with either AgNO₃ or CuCl under mild conditions. The intermediary gallium or indium tris(aryldithioate) complexes are easily prepared by stirring the appropriate metal and aryldithioc acid at room temperature. Overall, this two-step process is a simple solution-based method for transforming Ga and In metal into valuable ternary metallosulfide nanoparticles at relatively low temperatures.

Anisotropic 2D Cu2-x Se Nanocrystals from Dodecaneselenol and Their Conversion to CdSe and CuInSe2 Nanoparticles

We present the synthesis of colloidal anisotropic Cu_2-x Se nanocrystals (NCs) with excellent size and shape control, using the unexplored phosphine-free selenium precursor 1-dodecaneselenol (DDSe). This precursor forms lamellar complexes with Cu(I) that enable tailoring the NC morphology from 0D polyhedral to highly anisotropic 2D shapes. The Cu_2-x Se NCs are subsequently used as templates in postsynthetic cation exchange reactions, through which they are successfully converted to CdSe and CuInSe₂ quantum dots, nanoplatelets, and ultrathin nanosheets. The shape of the template hexagonal nanoplatelets is preserved during the cation exchange reaction, despite a substantial reorganization of the anionic sublattice, which leads to conversion of the tetragonal umangite crystal structure of the parent Cu_2-x Se NCs into hexagonal wurtzite CdSe and CuInSe₂, accompanied by a change of both the thickness and the lateral dimensions of the nanoplatelets. The crystallographic transformation and reconstruction of the product NCs are attributed to a combination of the unit cell dimensionalities of the parent and product crystal phases and an internal ripening process. This work provides novel tools for the rational design of shape-controlled colloidal anisotropic Cu_2-x Se NCs, which, besides their promising optoelectronic properties, also constitute a new family of cation exchange templates for the synthesis of shape-controlled NCs of wurtzite CdSe, CuInSe₂, and other metal selenides that cannot be attained through direct synthesis approaches. Moreover, the insights provided here are likely applicable also to the direct synthesis of shape-controlled NCs of other metal selenides, since DDSe may be able to form lamellar complexes with several other metals.

Achieving deep-red-to-near-infrared emissions in Sn-doped Cu-In-S/ZnS quantum dots for red-enhanced white LEDs and near-infrared LEDs

Semiconductor quantum dots (QDs) are promising luminescent materials for use in lighting, display and bio-imaging, and the color tuning is a necessity for such applications. In this work, we report tunable colors and deep-red or near infrared (NIR) emissions in Cu-In-S and Cu-In-S/ZnS QDs by incorporating Sn. These QDs (with a size of 5 nm) with varying Sn concentrations and/or Cu/In ratios were synthesized by a non-injection method, and characterized by a variety of analytical techniques (i.e., XRD, TEM, XPS, absorption, photoluminescence, decay time, etc.). The Cu-Sn-In-S and Cu-Sn-In-S/ZnS QDs with Cu/In = 1/2 show the emission maximum in the ranges of 701-894 nm and 628-785 nm, respectively. The red-shift in emission is ascribed to the decrease of the band gap with the Sn doping. The highest quantum yield of 75% is achieved in Cu-Sn-In-S/ZnS with 0.1 mmol Sn and Cu/In = 1/2. Both the white and NIR LEDs were fabricated by using Cu-Sn-In-S/ZnS QDs and a 365 nm LED chip. The white LED exhibits superhigh color rendering indices of Ra = 97.2 and R9 = 91 and a warm color temperature of 2700 K. And the NIR LED shows an interesting broadband near-infrared emission centered at 741 nm, allowing for applications in optical communication, sensing and medical devices.

Biocompatible Semiconductor Quantum Dots as Cancer Imaging Agents

Approximately 1.7 million new cases of cancer will be diagnosed this year in the United States leading to 600 000 deaths. Patient survival rates are highly correlated with the stage of cancer diagnosis, with localized and regional remission rates that are much higher than for metastatic cancer. The current standard of care for many solid tumors includes imaging and biopsy with histological assessment. In many cases, after tomographical imaging modalities have identified abnormal morphology consistent with cancer, surgery is performed to remove the primary tumor and evaluate the surrounding lymph nodes. Accurate identification of tumor margins and staging are critical for selecting optimal treatments to minimize recurrence. Visible, fluorescent, and radiolabeled small molecules have been used as contrast agents to improve detection during real-time intraoperative imaging. Unfortunately, current dyes lack the tissue specificity, stability, and signal penetration needed for optimal performance. Quantum dots (QDs) represent an exciting class of fluorescent probes for optical imaging with tunable optical properties, high stability, and the ability to target tumors or lymph nodes based on surface functionalization. Here, state-of-the-art biocompatible QDs are compared with current Food and Drug Administration approved fluorophores used in cancer imaging and a perspective on the pathway to clinical translation is provided.

From Large-Scale Synthesis to Lighting Device Applications of Ternary I-III-VI Semiconductor Nanocrystals: Inspiring Greener Material Emitters

Quantum dots with fabulous size-dependent and color-tunable emissions remained as one of the most exciting inventories in nanomaterials for the last 3 decades. Even though a large number of such dot nanocrystals were developed, CdSe still remained as unbeatable and highly trusted lighting nanocrystals. Beyond these, the ternary I-III-VI family of nanocrystals emerged as the most widely accepted greener materials with efficient emissions tunable in visible as well as NIR spectral windows. These bring the high possibility of their implementation as lighting materials acceptable to the community and also to the environment. Keeping these in mind, in this Perspective, the latest developments of ternary I-III-VI nanocrystals from their large-scale synthesis to device applications are presented. Incorporating ZnS, tuning the composition, mixing with other nanocrystals, and doping with Mn ions, light-emitting devices of single color as well as for generating white light emissions are also discussed. In addition, the future prospects of these materials in lighting applications are also proposed.

Mapping the Atomistic Structure of Graded Core/Shell Colloidal Nanocrystals

Engineering the compositional gradient for core/shell semiconductor nanocrystals improves their optical properties. To date, however, the structure of graded core/shell nanocrystal emitters has only been qualitatively described. In this paper, we demonstrate an approach to quantify nanocrystal structure, selecting graded Ag-In-Se/ZnSe core/shell nanocrystals as a proof-of-concept material. A combination of multi-energy small-angle X-ray scattering and electron microscopy techniques enables us to establish the radial distribution of ZnSe with sub-nanometer resolution. Using ab initio shape-retrieval analysis of X-ray scattering spectra, we further determine the average shape of nanocrystals. These results allow us to generate three-dimensional, atomistic reconstructions of graded core/shell nanocrystals. We use these reconstructions to calculate solid-state Zn diffusion in the Ag-In-Se nanocrystals and the lattice mismatch between nanocrystal monolayers. Finally, we apply these findings to propose design rules for optimal shell structure and record-luminescent core/shell nanocrystals.

Spectro-electrochemical Probing of Intrinsic and Extrinsic Processes in Exciton Recombination in I-III-VI2 Nanocrystals

Ternary CuInS₂ nanocrystals (CIS NCs) are attracting attention as nontoxic alternatives to heavy metal-based chalcogenides for many technologically relevant applications. The photophysical processes underlying their emission mechanism are, however, still under debate. Here we address this problem by applying, for the first time, spectro-electrochemical methods to core-only CIS and core/shell CIS/ZnS NCs. The application of an electrochemical potential enables us to reversibly tune the NC Fermi energy and thereby control the occupancy of intragap defects involved in exciton decay. The results indicate that, in analogy to copper-doped II-VI NCs, emission occurs via radiative capture of a conduction-band electron by a hole localized on an intragap state likely associated with a Cu-related defect. We observe the increase in the emission efficiency under reductive electrochemical potential, which corresponds to raising the Fermi level, leading to progressive filling of intragap states with electrons. This indicates that the factor limiting the emission efficiency in these NCs is nonradiative electron trapping, while hole trapping is of lesser importance. This observation also suggests that the centers for radiative recombination are Cu²⁺ defects (preexisting and/or accumulated as a result of photoconversion of Cu¹⁺ ions) as these species contain a pre-existing hole without the need for capturing a valence-band hole generated by photoexcitation. Temperature-controlled photoluminescence experiments indicate that the intrinsic limit on the emission efficiency is imposed by multiphonon nonradiative recombination of a band-edge electron and a localized hole. This process affects both shelled and unshelled CIS NCs to a similar degree, and it can be suppressed by cooling samples to below 100 K. Finally, using experimentally measured decay rates, we formulate a model that describes the electrochemical modulation of the PL efficiency in terms of the availability of intragap electron traps as well as direct injection of electrons into the NC conduction band, which activates nonradiative Auger recombination, or electrochemical conversion of the Cu²⁺ states into the Cu¹⁺ species that are less emissive due to the need for their "activation" by the capture of photogenerated holes.

Spectroscopic and Device Aspects of Nanocrystal Quantum Dots

The field of nanocrystal quantum dots (QDs) is already more than 30 years old, and yet continuing interest in these structures is driven by both the fascinating physics emerging from strong quantum confinement of electronic excitations, as well as a large number of prospective applications that could benefit from the tunable properties and amenability toward solution-based processing of these materials. The focus of this review is on recent advances in nanocrystal research related to applications of QD materials in lasing, light-emitting diodes (LEDs), and solar energy conversion. A specific underlying theme is innovative concepts for tuning the properties of QDs beyond what is possible via traditional size manipulation, particularly through heterostructuring. Examples of such advanced control of nanocrystal functionalities include the following: interface engineering for suppressing Auger recombination in the context of QD LEDs and lasers; Stokes-shift engineering for applications in large-area luminescent solar concentrators; and control of intraband relaxation for enhanced carrier multiplication in advanced QD photovoltaics. We examine the considerable recent progress on these multiple fronts of nanocrystal research, which has resulted in the first commercialized QD technologies. These successes explain the continuing appeal of this field to a broad community of scientists and engineers, which in turn ensures even more exciting results to come from future exploration of this fascinating class of materials.

Compound Copper Chalcogenide Nanocrystals

This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility. The outstanding functional properties of these materials stems from the relationship between their band structure and defect concentration, including charge carrier concentration and electronic conductivity character, which consequently affects their optoelectronic, optical, and plasmonic properties. This, combined with several metastable crystal phases and stoichiometries and the low energy of formation of defects, makes the reproducible synthesis of these materials, with tunable parameters, remarkable. Further to this, the review captures the progress of the hierarchical assembly of these NCs, which bridges the link between their discrete and collective properties. Their ubiquitous application set has cross-cut energy conversion (photovoltaics, photocatalysis, thermoelectrics), energy storage (lithium-ion batteries, hydrogen generation), emissive materials (plasmonics, LEDs, biolabelling), sensors (electrochemical, biochemical), biomedical devices (magnetic resonance imaging, X-ray computer tomography), and medical therapies (photochemothermal therapies, immunotherapy, radiotherapy, and drug delivery). The confluence of advances in the synthesis, assembly, and application of these NCs in the past decade has the potential to significantly impact society, both economically and environmentally.

Synthetic strategies and biomedical applications of I–III–VI ternary quantum dots

In this review, we discuss recent advances of I–III–VI QDs with a major focus on synthesis and biomedical applications; advantages include low toxicity and fluorescent tuning in the biological window.

Synthesis and Optical Properties of Lead-Free Cesium Tin Halide Perovskite Quantum Rods with High-Performance Solar Cell Application

Herein, the fabrication of a lead-free cesium tin halide perovskite produced via a simple solvothermal process is reported for the first time. The resulting CsSnX₃ (X = Cl, Br, and I) quantum rods show composition-tunable photoluminescence (PL) emissions over the entire visible spectral window (from 625 to 709 nm), as well as significant tunability of the optical properties. In this study, we demonstrate that through hybrid materials (CsSnX₃) with different halides, the system can be tunable in terms of PL. By replacing the halide of the CsSnX₃ quantum rods, a power conversion efficiency of 12.96% under AM 1.5 G has been achieved. This lead-free quantum rod replacement has demonstrated to be an effective method to create an absorber layer that increases light harvesting and charge collection for photovoltaic applications in its perovskite phase.

Synthesis of shape and size controlled copper indium diselenide (CuInSe2) via extrusion of selenium from 1,2,3-selenadiazole

CISe NPs were successfully synthesized via extrusion of selenium from 1,2,3-selenadiazole. The effect of various reaction parameters on the size and shape of CISe were studied.

Cu–In–Te and Ag–In–Te colloidal nanocrystals with tunable composition and size

An amide-promoted synthesis enables independent size and composition control for I–III–VI colloidal nanocrystals.

Phosphine-free synthesis of Ag-In-Se alloy nanocrystals with visible emissions

As promising heavy metal-free emitting materials, Ag-In-Se nanocrystals (NCs) are conventionally synthesized using organic phosphine agents and exhibit near-infrared emissions. In this work, we demonstrate a rapid phosphine-free approach for synthesizing Ag-In-Se alloy NCs with the emissions tunable to the visible region on the basis of the phosphine-free dissolution of Se powder. At room temperature, Se powder is reduced by dodecanethiol and dissolved in oleylamine to produce a Se precursor. The resultant Se precursor is highly active, which permits rapid synthesis at a relatively low temperature, such as at 90 °C for 150 s. By optimizing the size, structure, and composition, the photoluminescence quantum yield of the as-synthesized Ag-In-Se NCs is enhanced to up to 10%. The growth of the Ag-In-Se NCs involves composition and phase transition, which strongly depend on the reaction temperature. The Ag2Se nuclei form first, and the Ag-In-Se NCs are produced by doping In(3+) into the preformed Ag2Se nuclei. Tetragonal phase Ag-In-Se is obtained below 170 °C, while the orthorhombic phase appears over 190 °C. The potential of Ag-In-Se NCs as red emitting phosphors for lighting-emitting diodes is further demonstrated.

Independent Composition and Size Control for Highly Luminescent Indium-Rich Silver Indium Selenide Nanocrystals

Ternary I-III-VI nanocrystals, such as silver indium selenide (AISe), are candidates to replace cadmium- and lead-based chalcogenide nanocrystals as efficient emitters in the visible and near IR, but, due to challenges in controlling the reactivities of the group I and III cations during synthesis, full compositional and size-dependent behavior of I-III-VI nanocrystals is not yet explored. We report an amide-promoted synthesis of AISe nanocrystals that enables independent control over nanocrystal size and composition. By systematically varying reaction time, amide concentration, and Ag- and In-precursor concentrations, we develop a predictive model for the synthesis and show that AISe sizes can be tuned from 2.4 to 6.8 nm across a broad range of indium-rich compositions from AgIn11Se17 to AgInSe2. We perform structural and optical characterization for representative AISe compositions (Ag0.85In1.05Se2, Ag3In5Se9, AgIn3Se5, and AgIn11Se17) and relate the peaks in quantum yield to stoichiometries exhibiting defect ordering in the bulk. We optimize luminescence properties to achieve a record quantum yield of 73%. Finally, time-resolved photoluminescence measurements enable us to better understand the physics of donor-acceptor emission and the role of structure and composition in luminescence.