From Indium-Doped Ag2 S to AgInS2 Nanocrystals: Low-Temperature In Situ Conversion of Colloidal Ag2 S Nanoparticles and Their NIR Fluorescence

Cation exchange synthesis of AgBiS2 quantum dots for highly efficient solar cells

Silver bismuth sulfide (AgBiS2) nanocrystals have emerged as a promising eco-friendly, low-cost solar cell absorber material. Their direct synthesis often relies on the hot-injection method, requiring the application of high temperatures and vacuum for prolonged times. Here, we demonstrate an alternative synthetic approach via a cation exchange reaction. In the first-step, bis(stearoyl)sulfide is used as an air-stable sulfur precursor for the synthesis of small, monodisperse Ag2S nanocrystals at room-temperature. In a second step, bismuth cations are incorporated into the nanocrystal lattice to form ternary AgBiS2 nanocrystals, without altering their size and shape. When implemented into photovoltaic devices, AgBiS2 nanocrystals obtained by cation exchange reach power conversion efficiencies of up to 7.35%, demonstrating the efficacy of the new synthetic approach for the formation of high-quality, ternary semiconducting nanocrystals.

Extensive emission tuning and characterization of highly efficient CuInS2 quantum dots for white light-emitting diodes

Whole visible range emitting CuInS2/ZnS QDs were obtained with broad band-width and high luminous efficiency by altering the Cu/In ratio and coating ZnS layer. 1-Dodecanethiol (DDT) as a sulfur source in the ZnS coating process can inhibit the lattice defects caused by Zn2+ inter-diffusion, thus increasing the photoluminescence quantum yield (PL QY). Then the stability and lighting performance of white light-emitting diodes (WLEDs) based on these CuInS2/ZnS QDs were characterized. The optimized WLED device exhibited a moderate luminous efficacy (LE) (70.33 lm·W-1) and ultrahigh color qualities (CRI Ra = 92.7, R9 = 95.9, R13 = 96.3) with warm white at a correlated color temperature (CCT) of 4052 K.

Sequential, low-temperature aqueous synthesis of Ag-In-S/Zn quantum dots via staged cation exchange under biomineralization conditions

The development of high quality, non-toxic (i.e., heavy-metal-free), and functional quantum dots (QDs) via 'green' and scalable synthesis routes is critical for realizing truly sustainable QD-based solutions to diverse technological challenges. Herein, we demonstrate the low-temperature all-aqueous-phase synthesis of silver indium sulfide/zinc (AIS/Zn) QDs with a process initiated by the biomineralization of highly crystalline indium sulfide nanocrystals, and followed by the sequential staging of Ag⁺ cation exchange and Zn²⁺ addition directly within the biomineralization media without any intermediate product purification. Therein, we exploit solution phase cation concentration, the duration of incubation in the presence of In₂S₃ precursor nanocrystals, and the subsequent addition of Zn²⁺ as facile handles under biomineralization conditions for controlling QD composition, tuning optical properties, and improving the photoluminescence quantum yield of the AIS/Zn product. We demonstrate how engineering biomineralization for the synthesis of intrinsically hydrophilic and thus readily functionalizable AIS/Zn QDs with a quantum yield of 18% offers a 'green' and non-toxic materials platform for targeted bioimaging in sensitive cellular systems. Ultimately, the decoupling of synthetic steps helps unravel the complexities of ion exchange-based synthesis within the biomineralization platform, enabling its adaptation for the sustainable synthesis of 'green', compositionally diverse QDs.

Systematic synthesis of different-sized AgInS2/GaSxnanocrystals for emitting the strong and narrow excitonic luminescence

This paper presents for the first time the systematic synthesis of AgInS₂(AIS) nanocrystals (NCs) with different sizes of 2.6-6.8 nm just by controlling only the reaction temperature. The synthesis of AIS core NCs was carried out in 2 steps: (i) synthesis of Ag₂S NCs and then (ii) partial exchange of Ag⁺with In³⁺in the template Ag₂S NCs. For step (i), Ag₂S NCs of different sizes were synthesized by reaction of the Ag and S precursors at different temperatures of 30 °C to 130 °C, for the same reaction time of 30 min. For step (ii), AIS NCs were created by the exchange of Ag⁺with In³⁺at 120 °C for 60 min. Finally, GaS_xwas shelled on AIS core NCs to produce the AgInS₂/GaS_xcore/shell structures. The synthesized AIS/GaS_xNCs demonstrate the clear excitonic absorptions and strong, narrow excitonic luminescence peaking at 530-606 nm depending on the size of AIS core NCs.

Core Nanoparticle Engineering for Narrower and More Intense Band-Edge Emission from AgInS2/GaSx Core/Shell Quantum Dots

Highly luminescent silver indium sulfide (AgInS2) nanoparticles were synthesized by dropwise injection of a sulfur precursor solution into a cationic metal precursor solution. The two-step reaction including the formation of silver sulfide (Ag2S) nanoparticles as an intermediate and their conversion to AgInS2 nanoparticles, occurred during the dropwise injection. The crystal structure of the AgInS2 nanoparticles differed according to the temperature of the metal precursor solution. Specifically, the tetragonal crystal phase was obtained at 140 °C, and the orthorhombic crystal phase was obtained at 180 °C. Furthermore, when the AgInS2 nanoparticles were coated with a gallium sulfide (GaSx) shell, the nanoparticles with both crystal phases emitted a spectrally narrow luminescence, which originated from the band-edge transition of AgInS2. Tetragonal AgInS2 exhibited narrower band-edge emission (full width at half maximum, FWHM = 32.2 nm) and higher photoluminescence (PL) quantum yield (QY) (49.2%) than those of the orthorhombic AgInS2 nanoparticles (FWHM = 37.8 nm, QY = 33.3%). Additional surface passivation by alkylphosphine resulted in higher PL QY (72.3%) with a narrow spectral shape.

Hitherto-Unexplored Photodynamic Therapy of Ag2 S and Enhanced Regulation Based on Polydopamine In Vitro and Vivo

Given their superior penetration depths, photosensitizers with longer absorption wavelengths present broader application prospects in photodynamic therapy (PDT). Herein, Ag₂ S quantum dots were discovered, for the first time, to be capable of killing tumor cells through the photodynamic route by near-infrared light irradiation, which means relatively less excitation of the probe compared with traditional photosensitizers absorbing short wavelengths. On modification with polydopamine (PDA), PDA-Ag₂ S was obtained, which showed outstanding capacity for inducing reactive oxygen species (increased by 1.69 times). With the addition of PDA, Ag₂ S had more opportunities to react with surrounding O₂ , which was demonstrated by typical triplet electron spin resonance (ESR) analysis. Furthermore, the PDT effects of Ag₂ S and PDA-Ag₂ S achieved at longer wavelengths were almost identical to the effects produced at 660 nm, which was proved by studies in vitro. PDA-Ag₂ S showed distinctly better therapeutic effects than Ag₂ S in experiments in vivo, which further validated the enhanced regulatory effect of PDA. Altogether, a new photosensitizer with longer absorption wavelength was developed by using the hitherto-unexplored photodynamic function of Ag₂ S quantum dots, which extended and enhanced the regulatory effect originating from PDA.