Demonstration of Bulk Semiconductor Optical Properties in Processable Ag2S and EuS Nanocrystalline Systems (original) (raw)
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The structural and optical constants of Ag2S semiconductor nanostructure in the Far-Infrared
Chemistry Central Journal, 2015
Background: In this paper a template-free precipitation method was used as an easy and low cost way to synthesize Ag 2 S semiconductor nanoparticles. The Kramers-Kronig method (K-K) and classical dispersion theory was applied to calculate the optical constants of the prepared samples, such as the reflective index n(ω) and dielectric constant ε(ω) in Far-infrared regime. Results: Nanocrystalline Ag 2 S was synthesized by a wet chemical precipitation method. Ag 2 S nanoparticle was characterized by X-ray diffraction, Scanning Electron Microscopy, UV-visible, and FT-IR spectrometry. The refinement of the monoclinic β-Ag2S phase yielded a structure solution similar to the structure reported by Sadanaga and Sueno. The band gap of Ag 2 S nanoparticles is around 0.96 eV, which is in good agreement with previous reports for the band gap energy of Ag 2 S nanoparticles (0.9-1.1 eV). Conclusion: The crystallite size of the synthesized particles was obtained by Hall-Williamson plot for the synthesized Ag 2 S nanoparticles and it was found to be 217 nm. The Far-infrared optical constants of the prepared Ag 2 S semiconductor nanoparticles were evaluated by means of FTIR transmittance spectra data and K-K method.
Journal of Alloys and Compounds, 2019
The present work is concerned with synthesis of doped (Cd 2+ ions) and surface passivated (ZnS) AgInS 2 core/shell nanocrystals by hot-injection method. UV spectral analysis of the nanocrystals thus prepared revealed that compared to dopant, passivation does much better in enhancing the optical property. Among the nanocrystals that were prepared, the growth of shell over core (AgInS 2 /ZnS) enhanced the optical property of AgInS 2 considerably compared to dopant on either core or shell or both core-shell of nanocrystal. On the contrary, photoluminescence study revealed that doped AgInS 2 with surface passivation (AgInS 2 :Cd 2+ /ZnS) plays a critical role in increasing PL intensity compared to either dopant or passivation alone on AgInS 2. This inference is based on the fact that passivation was accompanied by decrease in surface-to-volume ratio that led to change in surface structure and crystal morphology. From XRD measurements we found that all the synthesized nanocrystals exhibited orthorhombic crystal structure with slight change in diffraction peak positions. The diffraction peak was shifted to lower angle with Cd 2+ ions dopant and higher angle with surface passivation. The change in diffraction pattern suggests the formation of AgInZnS/ZnS alloy of ZnS on AgInS 2 core. TEM images of pure AgInS 2 /ZnS and doped core/shell nanocrystals revealed that both pure and doped core/shell were irregular and sparingly mono-dispersed nanoparticles. EDX spectrum clearly revealed that pure and doped AgInS 2 /ZnS nanocrystals were composed of Ag, In, S, Zn and Cd ions in the synthesized systems. The formation of AgInS 2 /ZnS core/shell nanocrystals were confirmed from the experimental results and these nanocrystals might be a good material in many optoelectronics industrials and bio-imaging application in near future.
Optical properties of polycrystalline AgxGa2−xSe2 (0.4⩽x⩽1.6) thin films
Solar Energy Materials and Solar Cells, 2007
Polycrystalline thin films of Ag x Ga 2Àx Se 2 (0.4pxp1.6) were prepared onto cleaned glass substrates by the stacked elemental layer (SEL) deposition technique. All the films were annealed in situ at 300 1C for 15 min. The compositions of the films were measured by energy-dispersive analysis of X-ray (EDAX) method. The structural and optical properties of the films were ascertained by X-ray diffraction (XRD) and UV-VIS-NIR spectrophotometry (photon wavelength ranging from 300 to 2500 nm), respectively. The influence of the composition on the optical properties of the material has been investigated. Microstructural perfection is quite evident from the abrupt descent around specific energy of photons in the transmittance spectra. Stoichiometric or slightly silver-deficient films show optimum electron transition energy and minimum sub-band gap absorption.
Colloidal Ag2S nanocrystals (NCs) typically do not exhibit sharp excitonic absorption and emission. We first elucidate the reason behind this problem by preparing Ag2S NCs from nearly monodisperse CdS NCs employing cation exchange reaction. It was found that the defect-related midgap transitions overlap with excitonic transition, blurring the absorption spectrum. On the basis of this observation, we prepared nearly defect-free Ag2S NCs using molecular precursors. These defect-free Ag2S NCs exhibit sharp excitonic absorption, emission (quantum yield 20%) in near-infrared (853 nm) region, and improved performance of Ag2S quantum-dot-sensitized solar cells (QDSSCs). Samples with lower defects exhibit photoconversion efficiencies >1% and open circuit voltage of ∼0.3 V, which are better compared with prior reports of Ag2S QDSSCs. Femtosecond transient absorption shows pump−probe two-photon absorption above 630 nm and slow-decaying excited state absorption below 600 nm. Concomitantly, open-aperture z-scan shows strong two-photon absorption at 532 nm (coefficient 55 ± 3 cm/GW).
Studies on Nanocrystalline Ag2Se
Materials and Manufacturing Processes, 2006
Silver selenide nanocrystals were synthesized using a chemical route by the interaction of ammoniacal silver nitrate and sodium selenosulfate in aqueous medium. The prepared samples were characterized by XRD, EDXA, and TEM. UV-VIS absorption spectrum of the nanocrystals shows that the optical band gap of the material is 1.72 eV, which is quite larger than the bulk phase of the materials. Thermal analysis exhibits that the phase changes from to at the transition temperature 406 K. Electrical conduction and thermoelectric power measurements also show the presence of two distinct phases of the materials and characteristic changes in transport properties due to the nanosize of the materials.
Materials Science in Semiconductor Processing, 2015
The optical characteristics of AgInS 2 nanocrystals (NCs) synthesized in aqueous solutions in the presence of aliphatic mercaptoacids under stoichiometric conditions (at a [Ag]:[In]: [S] molar ratio of 1:1:2) have been studied with micro-Raman, optical absorption, photoluminescence (PL) and PL excitation spectroscopy. The X-ray diffraction (XRD) proved predominant formation of nanocrystals (NCs) of chalcopyrite AgInS 2 phase of the average diameter about 4 nm. Micro-Raman spectra confirmed formation of coexisting the chalcopyrite AgInS 2 and cubic AgIn 5 S 8 phases. The PL of the undoped and Zn-doped NCs embedded in polymer films of gelatin is found to be caused by defects localized in the NCs of two different ensembles each of which generates its own PL band. It is assumed that one of the ensembles is composed of the NCs of chalcopyrite phase and the other contains NCs of secondary phase, presumably of the cubic AgIn 5 S 8 .
10-Fold Quantum Yield Improvement of Ag2S Nanoparticles by Fine Compositional Tuning
ACS Applied Materials & Interfaces, 2020
This supplementary information includes the following sections: S1. Chemical conditions for the NPs production S2. XRD characterization of the synthesized NPs S3. XPS, XANEs and Fourier transform EXAFS of the NPs S5. PLQY measurements S4. Dose dependent experiment and performance comparison between optimized NPs and commercially available NPs
Characterization of Ag Nanocrystals for use in Solar Cell Applications
MRS Proceedings, 2009
Ag nanocrystals made by chemical synthesis have been used in solar cell applications as a part of light trapping. The shape, crystal structure, defects and composition of these nanocrystals have been studied in detail. Samples with different ratios of silver solution (AgNO 3 ) and reductant (NaBH4) were made, and a difference in nanocrystal size was observed. HRTEM and diffraction patterns showed that the samples contained mostly Ag nanocrystals, and some of them contained Ag 2 O nanocrystals as well. Some nanocrystals contained large defects, mostly twinning, which induced facets on the nanocrystal surface.