Thermal stability of Mn2+ ion luminescence in Mn-doped core-shell quantum dots

Dual-emissive luminescence in OIHMH single crystals: tunable red-green emissions via Mn2+ doping and theoretical insights

The burgeoning demand for materials with tunable photoluminescence properties for applications has necessitated the exploration of novel luminescent materials. This study presents the synthesis and characterization of a novel 0D organic-inorganic hybrid metal halide (OIHMH) single crystal, C6H14N2CdBr4, which exhibits intriguing luminescent properties upon Mn2+ doping. The introduction of single Mn2+ ions results in a dual-emission, with the unexpected emergence of a red emission peak at 627 nm, in addition to the conventional tetrahedral green emission at 525 nm. This dual-emission is attributed to the distinct inter-tetrahedral distances within the crystal structure of C6H14N2CdBr4 with varying distances between [CdBr4]2- tetrahedra, influencing the spatial distribution and interaction of the [MnBr4]2- tetrahedra. Electron paramagnetic resonance (EPR) spectroscopy and theoretical calculations reveal the 627 nm and 525 nm emissions are attributed to the d-d transition of magnetic coupled Mn2+-Mn2+ pairs and isolated Mn2+ ions, respectively. This study not only advances the understanding of the luminescence mechanisms of Mn2+ but also paves the way for the development of tunable luminescent materials.

Exciton-to-Dopant Energy Transfer Dynamics in Mn2+ Doped CsPbBr3 Nanowires Synthesized by Diffusion Doping

Mn2+ doped perovskite nanocrystals have garnered significant attention in optoelectronic applications. However, the synthesis of Mn2+ doped perovskite nanowires (NWs) poses challenges, and the dynamics of energy transfer from the exciton to Mn2+ remains unexplored, which is crucial for optimizing Mn2+ luminescence efficiency. Herein, we present a method to synthesize Mn2+ doped CsPbBr3 NWs with a photoluminescence quantum yield of 52% by diffusing Mn2+ into seed CsPbBr3 NWs grown via a hot injection method. We control the solution and lattice chemical potentials of Pb2+ and Mn2+ to enable Mn2+ to diffuse into the CsPbBr3 NWs while minimizing Ostwald ripening. Variable temperature photoluminescence spectroscopy reveals that the energy transfer from the exciton to Mn2+ in Mn2+ doped CsPbBr3 NWs is temperature dependent. A dynamic competition is observed between energy transfer and backward energy transfer, resulting in stronger Mn2+ photoluminescence at 80 K. This work provides a specific synthesis pathway for Mn2+ doped CsPbBr3 NWs and sheds light on their exciton-to-Mn2+ energy transfer dynamics.

Spectral Tunability, Luminescence Enhancement, and Temperature Sensitivity of Sb3+-Doped Bismuth-Based Halide Emission Crystals for Anti-Counterfeiting Applications

The synthesis of sustainable luminescent materials with simplicity, low energy consumption, and nontoxicity is of great importance in the field of chemistry and materials science. In this study, a room temperature evaporation method was employed to synthesize Sb3+-doped bismuth-based halide emission crystals, allowing for investigation of spectral tuning, luminescence enhancement, and temperature sensitivity. By substitution of Rb+ with varying concentrations of Cs+ in Rb3BiCl6 (RBC), the luminescent color of the crystals can be tuned from orange to yellow. The resulting alloyed yellow-emitting crystals were identified as Rb2CsBiCl6 (RCBC). Remarkably, when one-third of the Rb+ ions were replaced by Cs+ in the RBC, the crystals exhibited improved thermal stability and a 20-fold increase in luminescence intensity. The temperature-sensitive behavior was observed for RBC:Sb, with emission shifting from 590 to 574 nm upon heating while the yellow emission of RCBC:Sb exhibited no significant peak shift with temperature. Notably, the yellow emission of RBC:Sb could be reversibly converted back to orange light upon cooling to room temperature. In contrast, RCBC:Sb exhibited no significant peak shift with temperature. The differential temperature sensitivity between RBC:Sb and RCBC:Sb offers potential applications in anti-counterfeiting measures.

Ultralong Red Room-Temperature Phosphorescence of 2D Organic-Inorganic Metal Halide Perovskites for Afterglow Red LEDs and X-ray Scintillation Applications

Organic-inorganic metal hybrid perovskites (OIHPs) have emerged as a promising class of materials for next-generation optoelectronic applications. However, the realization of red and near-infrared (NIR) room-temperature phosphorescence (RTP) in these materials remains limited. In this study, a very strong red RTP emission centered at 610 nm is achieved by doping Mn2+ ions into Cd-based 2D OIHPs. Notably, the optimized B-EACC:Mn2+ exhibited a high quantum yield of 44.11%, an ultralong lifetime of up to 378 ms, and excellent stability against high temperatures and various solvents, surpassing most reported counterparts of 2D OIHPs. Moreover, the B-EACC:Mn2+ can be used as a red emitter for coating an ultraviolet light-emitting diode chip, exhibiting an observable afterglow to the naked eye for approximately 4 s. In addition, the B-EACC:Mn2+ demonstrates interesting characteristics under X-ray excitation, exhibiting X-ray response at radiation doses in the range of 34.75-278 μGy s-1. This work suggests the infinite possibility of doping guest ions to realize red RTP in 2D OIHPs, promoting the development of long-persistent phosphorescent emitters for multifunctional light-emitting applications.

Competing Energy Transfer in Two-Dimensional Mn2+-Doped BDACdBr4 Hybrid Layered Perovskites with Near-Unity Photoluminescence Quantum Yield

Two-dimensional (2D) hybrid layered perovskites (HLPs) have attracted extensive attention due to their excellent optoelectronic properties. Herein, we successfully prepared high-quality Mn-doped BDACdBr₄ (BDA = NH₂(CH₂)₄NH₂, butylene diammonium) HLP single crystals (SCs). The incorporation of Mn²⁺ ions modulates the electronic band structure of BDACdBr₄ perovskites and tailors the energy transfer process of excited states. A near-unity photoluminescence (PL) quantum yield of 96% from the Mn²⁺ emission at 608 nm is achieved. Excitation wavelength-dependent spectroscopic characterizations help to clarify the energy transfer mechanism of Mn-doped BDACdBr₄, in which competing PL from the ³E_g → ¹A_1g transition of Cd²⁺ and the ⁴T₁(G) → ⁶A₁(S) transition of Mn²⁺ dopants is observed. Temperature-dependent PL spectroscopic characterizations indicate that the efficient energy transfer from BDACdBr₄ perovskite host to Mn²⁺ dopants requires thermal activation to overcome a potential barrier. This work provides new insight into the photophysics and optical properties of 2D HLPs, especially the influence of Mn²⁺ doping on competing energy transfer in hybrid luminescent materials.

Highly Luminescent and Photostable Core/Shell/Shell ZnSeS/Cu:ZnS/ZnS Quantum Dots Prepared via a Mild Aqueous Route

An aqueous-phase synthesis of 3-mercaptopropionic acid (3-MPA)-capped core/shell/shell ZnSeS/Cu:ZnS/ZnS QDs was developed. The influence of the Cu-dopant location on the photoluminescence (PL) emission intensity was investigated, and the results show that the introduction of the Cu dopant in the first ZnS shell leads to QDs exhibiting the highest PL quantum yield (25%). The influence of the Cu-loading in the dots on the PL emission was also studied, and a shift from blue-green to green was observed with the increase of the Cu doping from 1.25 to 7.5%. ZnSeS/Cu:ZnS/ZnS QDs exhibit an average diameter of 2.1 ± 0.3 nm and are stable for weeks in aqueous solution. Moreover, the dots were found to be photostable under the continuous illumination of an Hg-Xe lamp and in the presence of oxygen, indicating their high potential for applications such as sensing or bio-imaging.

Suppressing thermal-quenching of lead halide perovskite nanocrystals by constructing wide-bandgap surface layer for achieving thermally stable white light-emitting diodes

Lead halide perovskite nanocrystals as promising ultrapure emitters are outstanding candidates for the next-generation light-emitting diodes (LED) and display applications, but the thermal quenching behavior of light emission has severely...

Hydrogen-Rich 2D Halide Perovskite Scintillators for Fast Neutron Radiography

A fast neutron has strong penetration ability through dense and bulky objects, which makes it an ideal nondestructive technology for detecting voids, cracks, or other defects inside large equipment. However, the lack of effective fast neutron detection materials limits its application. Perovskites have shown excellent optical properties in many areas, but they are absent from fast neutron detection imaging because they cannot directly absorb fast neutrons and emit luminescence. Here, we demonstrate a hydrogen-rich long-chain organic amine modified two-dimensional (2D) perovskite fast neutron scintillator, Mn-(C₁₈H₃₇NH₃)₂PbBr₄(Mn-STA₂PbBr₄). Its hydrogen density can reach 9.51 × 10²⁸ m^-3, and the photoluminescence quantum yield can reach 58.58%, so it is possible to integrate fast neutron absorption and luminescence into a single compound. More importantly, Mn-STA₂PbBr₄ can be made into a large-area self-supporting fast neutron scintillator plate with satisfactory spatial resolution (0.5 lp/mm (lp: line pairs)). This strategy provides a simple and promising choice for fast neutron scintillator nondestructive testing.

II-VI core/shell quantum dots and doping with transition metal ions as a means of tuning the magnetoelectronic properties of CdS/ZnS core/shell QDs: A DFT study

This paper examines the alterations in the properties of II-VI Quantum Dots (QDs) when these are coated with a shell made of another material of the same family and investigates the structural, electronic and magnetic properties of doped CdS/ZnS core/shell QDs. The core/shell QDs have been constructed by building the shell over the bare core QD and it is found that this construction of a shell over the bare QD can bring about dramatic changes in its optical properties. On changing the shell by varying either the cation or the anion, substantial variations are brought about in the band gap and electrophilicity. The trend of Fermi energies is more negative for core/shell QDs than for the QDs without a shell, and the value is almost the same for core/shell QDs with the same core. Swapping of the core and the shell materials brings greater stability in the case of shells of the wider band gap materials. Binding energy data demonstrates that the CdS/ZnS, CdSe/ZnSe, CdSe/CdS core/shell systems are more stable than ZnS/CdS, ZnSe/CdSe, CdS/CdSe core/shell systems, respectively. An augmentation in the properties is found on doping the QD with transition metal ions. The binding energies are found to be functions of the kind of dopant as well as the spin multiplicity and account for the stability of one spin state over the other at a specific site of the QD. The most fascinating property that plays a decisive role in the extant work is the introduction of magnetism in core/shell QDs as a result of the entry of unpaired electrons within the CdS/ZnS QDs on doping with transition metal ions. The deviation of the observed magnetic moments from the expected values increases as the dopant is varied from Mn²⁺ to Fe²⁺ to Co²⁺ to Ni²⁺ to Cu²⁺. Hirshfeld charge analysis shows that the doped ion accepts negative charge from the sulfide ions in the core, with the smallest charge transfer seen in the case of Hg²⁺ ions. As we move from Mn²⁺ to Hg²⁺, the trend followed for the Hirshfeld charges indicates that the overall charge on the core is lower and that on the shell is higher for all the doped cases in comparison to the undoped CdS/ZnS core/shell QD. The band gap values reveal that the Fe²⁺ doped CdS/ZnS core/shell structures have the smallest band gaps. Hence, we expect that this paper will help researchers to develop a strategy to produce QDs of the anticipated properties for various applications, and transition metal ions can be successfully employed for modification of various magnetoelectronic properties of the host semiconductor for future applications in nanotechnology.

Linear and Nonlinear Optical Absorption of CdSe/CdS Core/Shell Quantum Dots in the Presence of Donor Impurity

Linear and nonlinear optical properties in colloidal CdSe/CdS core/shell quantum dots with different sizes have been theoretically investigated in the framework of effective mass approximation. The electron states in colloidal CdSe/CdS core/shell quantum dots have been calculated using the finite element method. The intraband linear and nonlinear absorption spectra have been calculated for colloidal CdSe/CdS core/shell quantum dots with different sizes. In addition, the dependences of the linear and nonlinear refractive index change on the incident light energy have been calculated. In the last section of the paper the second- and third-order harmonic generation spectra have been presented.

Near-unity blue-orange dual-emitting Mn-doped perovskite nanocrystals with metal alloying for efficient white light-emitting diodes

The tunable dual-color emitting Mn²⁺ doped CsPbCl_3-xBr_x nanocrystals (NCs) with near-unity photoluminescence quantum yield (PL QY) were synthesized through post-treatment of metal bromide at room temperature for fabrication of efficient warm white light-emitting diodes (WLEDs). Especially, the CdBr₂ treated blue-orange emitting Mn doped NCs with various Mn/Pb molar feed ratios exhibit higher PL QY of 97% and longer Mn²⁺ PL lifetime of 0.9 ms. It is surprisingly found that the X-ray diffraction peak at 31.9° is almost not changed with increasing Br composition, meaning formation of metal alloying due to incorporation of amount of divalent cation in NCs. The strong and stable Mn²⁺ PL at temperature ranging from 80 K to 360 K are revealed and the temperature-dependent energy transfer efficiencies in Mn²⁺ doped CsPbCl_1.5Br_1.5 NCs are obtained. The enhancement mechanism of Mn²⁺ PL QY was attributed to improved energy transfer from exciton to Mn²⁺ d-d transition and suppressed defect state density after post-treatment. The efficient warm WLEDs with color rendering index of 90 and luminous efficacy of 92 lm/W at 10 mA were fabricated by combining blue-orange dual-emitting Mn²⁺ doped CsPbCl_3-xBr_x@SiO₂ and green emissive CsPbBr₃@SiO₂ NCs with violet GaN chips.

Exciton-Related Raman Scattering, Interband Absorption and Photoluminescence in Colloidal CdSe/CdS Core/Shell Quantum Dots Ensemble

By using the numerical discretization method within the effective-mass approximation, we have theoretically investigated the exciton-related Raman scattering, interband absorption and photoluminescence in colloidal CdSe/CdS core/shell quantum dots ensemble. The interband optical absorption and photoluminescence spectra have been revealed for CdSe/CdS quantum dots, taking into account the size dispersion of the ensemble. Numerical calculation of the differential cross section has been presented for the exciton-related Stokes–Raman scattering in CdSe/CdS quantum dots ensemble with different mean sizes.

Novel synthesis of Mn: ZnSe@ZnS core-shell quantum dots based on photoinduced fluorescence enhancement

A novel Type-I Mn: ZnSe@ZnS core-shell quantum dots (QDs) was reported through a two-step procedure by using low-cost inorganic salts and naturalbiomacromolecule as raw materials. Based on a designed structure of L-cysteine-capped Mn: ZnSe QDs in aqueous media with the controllable surface, Mn: ZnSe@ZnS core-shell QDs were formed due to photoactive ions and defect curing under continuous constant light. The influences of experimental variables, including synthesis conditions of Mn: ZnSe QDs, different types and affecting factors of photo irradiation had been systematically investigated. Under the effect of photoinduced fluorescence enhancement, the photoluminescence (PL) intensity increases significantly by about 5-10 times after 1-3 h of UV irradiation. The position of the fluorescence peak was red-shifted by about 17 nm, emitting orange-red fluorescence. The photoluminescence quantum yield (PL QY) was markedly improved (up to 35%). The structure and morphology of Mn: ZnSe@ZnS core-shell QDs were also confirmed by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS) in detail. The mechanism of photoinduced fluorescence enhancement was attributed to L-cysteine allowed to release S^2- to form a ZnS shell, and the passivated surface non-radiative relaxation centers of Mn: ZnSe@ZnS QDs was successfully synthesized with highuniform size, excellent photoluminescence performance, and good stability, all ofwhichmakethemgood potential candidates for white LEDs, and biological labels.

Synthesis of highly luminescent Mn-doped CsPbCl3 nanoplatelets for light-emitting diodes

An atmospheric approach is reported to synthesize Mn-doped CsPbCl₃ nanoplatelets with high PLQYs, and their applications in soft polymers and LEDs.

Sequential Improvement from Cosolvents Ink Formulation to Vacuum Annealing for Ink-Jet Printed Quantum-Dot Light-Emitting Diodes

Optimization of ink-jet printing conditions of quantum-dot (QD) ink by cosolvent process and improvement of quantum-dot light-emitting diodes (QLEDs) characteristics assisted by vacuum annealing were analyzed in this research. A cosolvent process of hexane and ortho-dichlorobenzene (oDCB) was optimized at the ratio of 1:2, and ink-jetting properties were analyzed using the Ohnesorge number based on the parameters of viscosity and surface tension. However, we found that these cosolvents systems cause an increase in the boiling point and a decrease in the vapor pressure, which influence the annealing characteristics of the QD emission layer (EML). Therefore, we investigated QLEDs' performance depending on the annealing condition for ink-jet printed QD EML prepared using cosolvents systems of hexane and oDCB. We enhanced the quality of QD EML and device performance of QLEDs by a vacuum annealing process, which was used to prevent exposure to moisture and oxygen and to promote effective evaporation of solvent in QD EML. As a result, the characteristics of QLEDs formed using ink-jet printed QD EML annealed under vacuum environment increased luminescence (L), current efficiency (CE), external quantum efficiency (EQE), and lifetime (LT50) by 30.51%, 33.7%, 21.70%, and 181.97%, respectively, compared to QLEDs annealed under air environment.

Bifunctional Passivation Strategy to Achieve Stable CsPbBr3 Nanocrystals with Drastically Reduced Thermal-Quenching

The thermal quenching behavior (temperature-dependent luminescence) has severely hindered the practical applications of CsPbX₃ nanocrystals. Here, we find that a simple surface treatment using ammonium hexafluorosilicate (AHFS, (NH₄)₂SiF₆) can drastically reduce the thermal quenching of CsPbBr₃ nanocrystals (CPB-NCs) while enhancing their photostability. The AHFS-treated sample sustains 90% of its original emission intensity as the temperature rises to 353 K, which is much better than that (17%) of the pristine sample. Meanwhile, the thermally stable AHFS-treated sample could maintain 93% of its initial PL emission after a 450 nm LED illumination of 53 h. Structural and surface characterizations indicate that the hydrolyzable AHFS absorbed on the surface could lead to a bifunctional passivation for CPB-NCs, through fluoride ions and its hydrolyzed product of silica, which can reduce the thermal quenching by limiting thermally activated carriers trapping into vacancies and block the attack from external environmental factors.

Epitaxial growth and defect repair of heterostructured CuInSexS2-x/CdSeS/CdS quantum dots

Heterostructured quantum dots (hetero-QDs) have outstanding optical properties and chemical/photostability, which make them promising building blocks for use in various optoelectronic devices. Here, CuInSe_xS_2-x/CdSeS/CdS hetero-QDs were synthesized through a facile two-step method. Their particle size, three-dimensional (3D) shapes and the epitaxial relationship between the CuInSe_xS_2-x/CdSeS core and CdS shell were investigated by high-resolution transmission electron microscopy (HRTEM). Our investigation proves that the as-synthesized hetero-QDs have a regular tetrahedron 3D shape with four {111} crystal facets. The epitaxial relationship between the CuInSe_xS_2-x/CdSeS core and CdS shell is determined to be [110]_core//[110]_shell, {112}_core//{111}_shell. In situ HRTEM observations show that the screw dislocation inside the hetero-QDs can be efficiently repaired using e-beam irradiation. These results may help in designing hetero-QDs with high-quality interfaces and identifying the strategies for synthesizing defect-free hetero-QDs.

Tunable photoluminescence and an enhanced photoelectric response of Mn2+-doped CsPbCl3 perovskite nanocrystals via pressure-induced structure evolution

Mn²⁺:CsPbCl₃ nanocrystals (NCs) were synthesized using a modified one-pot injection method, which exhibits significantly improved thermal stability. For the first time, the pressure-treated optical and structural properties of synthetic Mn²⁺:CsPbCl₃ NCs were further investigated, and their associated intriguing electrical and photoelectric properties were revealed from impedance spectra and photocurrent measurements under compression. The pressure-dependent photoluminescence experienced an initial redshift before 1.7 GPa followed by a continuous blueshift, as evidenced by the bandgap shifts. High-pressure XRD spectra uncovered a cubic-to-orthorhombic structural transition at about 1.1 GPa and subsequent amorphization upon further compression, which was fully reversible. Furthermore, the sample annealing from 340 K drove grain growth and decreased grain boundary resistance at ambient pressure. The compression further decreased the grain boundary barrier and improved the electrical conductivity (up to ∼10^-2Ω^-1 cm^-1) of the thermally annealed Mn²⁺:CsPbCl₃ NC surface. Simultaneous photocurrent enhancement of thermally annealed NCs was also achieved as expected, and reached optimal performance at 0.7 GPa. Strikingly, after the pressure cycling (loading-releasing), the results show that thermally annealed Mn²⁺:CsPbCl₃ NCs gained preservable higher electrical conductivity (∼10 times increase) and an improved photoelectric response compared to the ambient state before compression. This work proves that high pressure is useful for opening the versatility in the structure and properties of metal-halide perovskite nanocrystals leading to a promising way for superior optoelectronic materials-by-design.

High-Performance Quantum Dots with Synergistic Doping and Oxide Shell Protection Synthesized by Cation Exchange Conversion of Ternary-Composition Nanoparticles

The insertion of cation impurities into quantum dots (QDs) as a dopant has been proved to be an efficient way to tailor their optical, electronic, and magnetic properties; however, the low quantum yield (QY) and poor photostability strongly limit their further applications. We report a strategy to coat a thin oxide shell around the heterovalent doped QDs to enhance their QYs and photostabilities simultaneously. In the case of Ag⁺-doped CdS QDs, the controlled cation exchange reaction between Cd²⁺ and ternary Ag₃SbS₃ nanoparticles not only realizes the Ag⁺ doping in CdS QDs but also generates a thin Sb₂O₃ shell around the surface of the QDs. Enabled by such, as-prepared CdS:Ag@Sb₂O₃ QDs exhibited enhanced photostability and high QY of 66.5%. We envision that the findings presented here will inspire more novel protocols for advancing the practical applications of doped QDs.

Single-channel UV/vis dual-band detection with ZnCdS:Mn/ZnS core/shell quantum dots

In the ultraviolet detection system, the Si-based photodetector could be sensitised with different kinds of fluorescent material to enhance its response in the short-wavelength range. Thick-shell ZnCdS:Mn/ZnS core/shell quantum dots (QDs) exhibit unique advantages in UV signal sensitisation due to their long PL lifetime, as well as stable emission matched with CCD's response. Herein, a single-channel UV panoramic detection system based on these Mn-doped QDs has been proposed. The QDs@PMMA film was attached on a Si-based CCD camera versus a tapered fibre, and an optical chopper was mounted before the QDs@PMMA film. The long lifetime fluorescence originating from UV signal could be still collected by the CCD camera when the chopper is in the 'off' state, hence the UV/vis signal ratio is significantly enhanced.

Enhanced luminescence and energy transfer in Mn2+ doped CsPbCl3-xBrx perovskite nanocrystals

Manganese ion (Mn²⁺) doped CsPbCl_3-xBr_x nanocrystals (NCs) with dual emissions have emerged as a promising candidate for white light emitting devices. The luminescence properties of Mn²⁺ doped CsPbCl_3-xBr_x NCs were studied by steady-state and time-resolved photoluminescence (PL) spectroscopy at temperature ranging from 80 to 300 K. The Mn²⁺ doped NCs with varied Br compositions were synthesized by means of Cl-to-Br anion exchange. The obtained doped NCs exhibited a tunable narrow band-edge emission band from 405 to 500 nm with a lengthened PL lifetime and a wide Mn²⁺ emission band at 600 nm with a shortened PL lifetime as the Br composition increases. It was interestingly found that PL intensity of the Mn²⁺ emission band was significantly enhanced by replacing Cl ions with Br and reached the maximum value in Mn²⁺:CsPbCl_2.15Br_0.85 NCs. Especially at low temperature (80 K), the intensity ratios of Mn²⁺ emission to band-edge emission increased ∼80 times in Mn²⁺:CsPbCl_2.15Br_0.85 NCs, compared with Mn²⁺:CsPbCl₃ ones. The temperature-dependent energy-transfer efficiencies of Mn²⁺:CsPbCl₃ and Mn²⁺:CsPbCl_2.15Br_0.85 NCs from excitons in NCs to Mn²⁺ ions were obtained. The PL enhancement of Mn²⁺ in CsPbCl_3-xBr_x NCs was attributed to Br composition-dependent exciton energy transfer to Mn²⁺.

Effect of surface/interfacial defects on photo-stability of thick-shell CdZnSeS/ZnS quantum dots

High color-purity CdZnSeS alloy cores and CdZnSeS/ZnS core/shell quantum dots (QDs) with 3, 11 and 17 monolayer (ML) ZnS shells are synthesized, and the narrow emission (full-width at half-maximum: ∼21 nm) is ascribed to the high size uniformity of QDs and the narrow linewidth of single QD spectra. Ultraviolet (UV) irradiation experiments show that the photo-stabilities of the samples improve remarkably with increasing shell thickness, but the photo-stability clearly decreases when the shell thickness is further increased to 17 MLs. Spectroelectrochemical (SEC) measurements indicate that the exciton recombination of QDs is mainly affected by surface electronic traps, and the interaction between exciton recombination centers and surface traps is significantly weakened with the increase in shell thickness due to the decreased wave function overlap of the exciton and surface traps. In the case of the 17 ML shell, the reduced photo-stability is due to increased interfacial defects caused by stress release during UV illumination, which can be proved by high-resolution transmission electron microscopy images and X-ray diffraction patterns. Furthermore, based on QDs' theoretical mass calculations, a photo-stable white light-emitting diode is fabricated by encapsulating with a thick-shell QD, and an exceptional color gamut of 130% relative to the National Television Systems Committee color space can be achieved. Also, its colorimetry and photometry are discussed in detail.

Synthesis of alloyed Zn1–xMnxS nanowires with completely controlled compositions and tunable bandgaps

This study reported the successful synthesis of Zn_1–xMn_xS nanowires with completely controlled compositions (0 ≤ x ≤ 1); the x values could be well controlled by tuning the feeding ratio of [(C₄H₉)₂NCS₂]₂Zn to [(C₄H₉)₂NCS₂]₂Mn precursors.

Ultrafast spectroscopic studies of composition-dependent near-infrared-emitting alloyed CdSeTe quantum dots

In this study, ultrafast optical properties of composition-dependent near infrared-emitting alloyed CdSeTe quantum dots are measured and analyzed.

Mass production of Mn2+-doped CsPbCl3 perovskite nanocrystals with high quality and enhanced optical performance

A novel microwave-assisted hot injection strategy for mass production of high quality Mn²⁺:CsPbCl₃ NCs was reported.

Impurity Location-Dependent Relaxation Dynamics of Cu:CdS Quantum Dots

Various types of 2% Cu-incorporated CdS (Cu:CdS) quantum dots (QDs) with very similar sizes have been prepared via a water soluble colloidal method. The locations of Cu impurities in CdS host nanocrystals have been controlled by adopting three different synthetic ways of doping, exchange, and adsorption to understand the impurity location-dependent relaxation dynamics of charge carriers. The oxidation state of incorporated Cu impurities has been found to be +1 and the band-gap energy of Cu:CdS QDs decreases as Cu2S forms at the surfaces of CdS QDs. Broad and red-shifted emission with a large Stokes shift has been observed for Cu:CdS QDs as newly produced Cu-related defects become luminescent centers. The energetically favored hole trapping of thiol molecules, as well as the local environment, inhibits the radiative recombination processes of Cu:CdS QDs, thus resulting in low photoluminescence. Upon excitation, an electron is promoted to the conduction band, leaving a hole on the valence band. The hole is transferred to the Cu+ d-state, changing Cu+ into Cu2+, which then participates in radiative recombination with an electron. Electrons in the conduction band are ensnared into shallow-trap sites within 52 ns. The electrons can be further captured on the time scale of 260 ns into deep-trap sites, where electrons recombine with holes in 820 ns. Our in-depth analysis of carrier relaxation has shown that the possibilities of both nonradiative recombination and energy transfer to Cu impurities become high when Cu ions are located at the surface of CdS QDs.

Mn Doped AIZS/ZnS Nanocrystals: Synthesis and Optical Properties

In this work, Mn doped AIZS/ZnS (Mn:AIZS/ZnS) nanocrystals (NCs) have been synthesized in an approach using heat-up and drop-wise addition of precursors. On the basis of the characterization of these doped NCs on their optical properties and materials, it is found that: (1) as more Mn atoms are doped into NCs, the doped NCs present photoluminescence (PL) red-shift and quantum yield quenching; (2) the doped NCs possess a short PL lifetime in tens of microseconds and a long PL lifetime in hundreds of microseconds, and the short lived PL is more dominant than the long lived one; and (3) the doped NCs present a reversible PL thermal quenching in a range from room temperature to 170°C. Possible PL mechanisms of these NCs were discussed by analyzing their time-resolved PL spectra and thermal stability.

Thermal degradation of luminescence in inorganic perovskite CsPbBr3nanocrystals

The PL degradation of annealed CsPbBr₃NCs is related to both the formation of surface defects and growth of NCs.

Synthesis and Characterization of Mn:ZnSe/ZnS/ZnMnS Sandwiched QDs for Multimodal Imaging and Theranostic Applications

In this work, a facile aqueous synthesis method is optimized to produce Mn:ZnSe/ZnS/ZnMnS sandwiched quantum dots (SQDs). In this core-shell co-doped system, paramagnetic Mn(2+) ions are introduced as core and shell dopants to generate Mn phosphorescence and enhance the magnetic resonance imaging signal, respectively. T1 relaxivity of the nanoparticles can be improved and manipulated by raising the shell doping level. Steady state and time-resolved optical measurements suggest that, after high level shell doping, Mn phosphorescence of the core can be sustained by the sandwiched ZnS shell. Because the SQDs are free of toxic heavy metal compositions, excellent biocompatibility of the prepared nanocrystals is verified by in vitro MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. To explore the theranostic applications of SQDs, liposome-SQD assemblies are prepared and used for ex vivo optical and magnetic resonance imaging. In addition, these engineered SQDs as nanocarrier for gene delivery in therapy of Panc-1 cancer cells are employed. The therapeutic effects of the nanocrystals formulation are confirmed by gene expression analysis and cell viability assay.

Temperature-dependent photoluminescence of inorganic perovskite nanocrystal films

The photoluminescence stability of all-inorganic perovskite nanocrystals (CsPbBr₃) with different size is studied.

Thermal stability of photoluminescence in Cu-doped Zn–In–S quantum dots for light-emitting diodes

Recombination between the donor–acceptor pair and/or between the host conduction band and the Cu ion state contributes to the emission of Cu:Zn–In–S QDs.

Photoluminescence properties of transition metal-doped Zn–In–S/ZnS core/shell quantum dots in solid films

The photoluminescence (PL) properties of transition metal ion (Mn²⁺ or Cu⁺) doped Zn–In–S/ZnS core/shell quantum dots (QDs) in solution and solid films were investigated by using steady-state and time-resolved PL spectra.

Dual emissive manganese and copper Co-doped Zn-In-S quantum dots as a single color-converter for high color rendering white-light-emitting diodes

Novel white light emitting diodes (LEDs) with environmentally friendly dual emissive quantum dots (QDs) as single color-converters are one of the most promising high-quality solid-state lighting sources for meeting the growing global demand for resource sustainability. A facile method was developed for the synthesis of the bright green-red-emitting Mn and Cu codoped Zn-In-S QDs with an absorption bangdgap of 2.56 eV (485 nm), a large Stokes shift of 150 nm, and high emission quantum yield up to 75%, which were suitable for warm white LEDs based on blue GaN chips. The wide photoluminescence (PL) spectra composed of Cu-related green and Mn-related red emissions in the codoped QDs could be controlled by varying the doping concentrations of Mn and Cu ions. The energy transfer processes in Mn and Cu codoped QDs were proposed on the basis of the changes in PL intensity and lifetime measured by means of steady-state and time-resolved PL spectra. By integrating these bicolor QDs with commercial GaN-based blue LEDs, the as-fabricated tricolor white LEDs showed bright natural white light with a color rendering index of 95, luminous efficacy of 73.2 lm/W, and color temperature of 5092 K. These results indicated that (Mn,Cu):Zn-In-S/ZnS QDs could be used as a single color-converting material for the next generation of solid-state lighting.

Facile synthesis of Ag-doped ZnCdS nanocrystals and transformation into Ag-doped ZnCdSSe nanocrystals with Se treatment

High-quality, pure, and color-tunable Ag:ZnCdS nanocrystals are prepared by optimization of the experimental conditions, and they can be further transformed into Ag:ZnCdSSe nanocrystals with Se treatment.

“Flash” synthesis of “giant” Mn-doped CdS/ZnS nanocrystals for high photostability

“Flash” synthesis of “giant” Mn-doped CdS/ZnS nanocrystals with high photostability is developed for the application in white LEDs.

Long-lived and well-resolved Mn²⁺ ion emissions in CuInS-ZnS quantum dots

CuInS₂ (CIS) quantum dots (QDs) have tunable photoluminescence (PL) behaviors in the visible and near infrared spectral range with markedly lower toxicity than the cadmium-based counterparts, making them very promising applications in light emitting and solar harvesting. However, there still remain material- and fabrication- related obstacles in realizing the high-performance CIS-based QDs with well-resolved Mn²⁺d-d emission, long emission lifetimes as well as high efficiencies. Here, we demonstrate the growth of high-quality Mn²⁺-doped CuInS-ZnS (CIS-ZnS) QDs based on a multi-step hot-injection strategy. The resultant QDs exhibit a well-resolved Mn²⁺d-d emission with a high PL quantum yield (QY) up to 66% and an extremely long excited state lifetime up to ~3.78 ms, which is nearly two times longer than the longest one of “green” QDs ever reported. It is promising that the synthesized Mn²⁺-doped CIS-ZnS QDs might open new doors for their practical applications in bioimaging and opto/electronic devices.

Efficient white light emitting diodes based on Cu-doped ZnInS/ZnS core/shell quantum dots

We report the fabrication of efficient white light-emitting diodes (WLEDs) based on Cu : ZnInS/ZnS core/shell quantum dots (QDs) with super large Stokes shifts. The composition-controllable Cu : ZnInS/ZnS QDs with a tunable emission from deep red to green were prepared by a one-pot noninjection synthetic approach. The high performance Cu : ZnInS QD-WLEDs with the colour rendering index up to 96, luminous efficacy of 70-78 lm W(-1), and colour temperature of 3800-5760 K were successfully fabricated by integration of red and green Cu-doped QDs. Negligible energy transfer between Cu-doped QDs was clearly found by measuring the photoluminescence lifetimes of the QDs, consistent with the small spectral overlap between QD emission and absorption. The experimental results indicated low toxic Cu : ZnInS/ZnS QDs could be suitable for solid state lighting.

Davydov splitting in cadmium vacancy emission, ferromagnetism and photosensitivity in manganese incorporated CdS nanocrystals

Surfactant and diamines-assisted CdS nanocrystals have Cd²⁺ vacancies with photoluminescence property. The neighbouring Cd²⁺–Cd²⁺ vacancies exhibit Davydov splitting. Addition of Mn²⁺ ions in these sites leads to ferromagnetism.

Temperature-dependent photoluminescence properties of Mn:ZnCdS quantum dots

We report the temperature-dependent photoluminescence of Mn:ZnCdS QDs with a high PL QY of 65% at 360 K.