We report a rigorous analytical approach based on one-particle phonon confinement model to realize direct detection of nanocrystal size distribution and volume fraction by using Raman spectroscopy. For the analysis, we first project the analytical confinement model onto a generic distribution function, and then use this as a fitting function to extract the required parameters from the Raman spectra, i.e., mean size and skewness, to plot the nanocrystal size distribution. Size distributions for silicon nanocrystals are determined by using the analytical confinement model agree well with the one-particle phonon confinement model, and with the results obtained from electron microscopy and photoluminescence spectroscopy. The approach we propose is generally applicable to all nanocrystal systems, which exhibit size-dependent shifts in the Raman spectrum as a result of phonon confinement.

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Direct characterization of nanocrystal size distribution using Raman spectroscopy

Since precise control of nanoscale features is in high demand, it is being exploited to develop and improve OSL dosimetric materials, where striking improvement might also be expected in lanthanide-doped metal halides. The major challenge in the development of a nanophosphor lies in avoiding the aggregation of a dopant element in host materials, which has long prevented an in-depth exploration for the same purpose. This study focuses on the synthesis and characterization of Sm-doped KCl nanophosphors to develop a novel accession to investigate the highly sensitive trivalent Sm-doped KCl phosphor. Herein, we were able to overcome the aggregation phenomena and we showed that Sm-doped KCl with 0.45 mol% of Sm, which is the optimised dopant concentration, exhibits the high-intensity luminescence performance under blue light stimulation for the gamma doses in the range from 100 mGy to 1000 Gy. This sensitivity is attributed to the uniform nanospheres encapsulated in KCl along with the predominant existence of a trivalent (Sm3+) state, where these conditions can introduce additional defects centres. The presence of these additional defect centres was confirmed by photoluminescence studies, plausibly supporting the charge transfer due to the optical energy between these states, leading to high sensitivity. To establish KCl:Sm as a good OSL dosimetric materials (DM), we investigated fading, reusability, and reproducibility and compared these with those of commercial DM compounds such as Al2O3:C and BeO. Overall, Sm-doped KCl is non-toxic, cost-effective, robust, and a promising candidate for reusable dosimetry.

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Facile synthesis of KCl:Sm3+ nanophosphor as a new OSL dosimetric material achieved through charge transfer between the defect states

Thin films of CZTS and CdS have been synthesized at optimized process parameters using radio frequency sputtering. These films were characterized using the variety of techniques for their structural, morphology, electric transport, and optical properties. Low angle-XRD and Raman spectroscopy analysis revealed the formation of a single phase of kesterite-CZTS and highly pure hexagonal CdS films. The HR-TEM analysis shows that both CZTS and CdS films are highly crystalline. The optical band gap was found to be ∼ 1.5 eV for CZTS and ∼ 2. 35 eV for CdS films. The cyclic voltammetry (CV) investigations on drop-casted optimized CZTS and CdS on Au electrodes have been performed to determine electrochemical band gap as well as band edge parameters. It has been observed that electrochemical band gap values from CV measurements are in good agreement with the optical band gap values estimated using UV–Visible spectroscopy. Finally, values of conduction band offset (CBO) and valence band offset have been calculated using band edge parameters which are measured by CV analysis. Band bending induced by CdS/CZTS hetero-junction formation leads to spike like CBO of ∼ 0.55 eV which can suitable for solar cells and expected to enhance photovoltaic performance.

CZTS/CdS: interface properties and band alignment study towards photovoltaic applications

The magnetic properties of metal-functionalized graphitic carbon nitride nanotubes were investigated based on first-principles calculations. The graphitic carbon nitride nanotube can be either ferromagnetic or antiferromagnetic by functionalizing with different metal atoms. The W- and Ti-functionalized nanotubes are ferromagnetic, which are attributed to carrier-mediated interactions because of the coupling between the spin-polarized d and p electrons and the formation of the impurity bands close to the band edges. However, Cr-, Mn-, Co-, and Ni-functionalized nanotubes are antiferromagnetic because of the anti-alignment of the magnetic moments between neighboring metal atoms. The functionalized nanotubes may be used in spintronics and hydrogen storage.

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Metal-functionalized single-walled graphitic carbon nitride nanotubes: a first-principles study on magnetic property

Cadmium sulphide (CdS) quantum dots were successfully synthesized in an ambient condition through chemical precipitation technique under methanolic medium. Quantum confinement effect was achieved using cetyltrimethyl ammonium bromide (CTAB) which would be used as a stabilizing agent. In this article, we report the effect of annealing temperature on structural, morphology and optical properties of CdS nanoparticles. In this esteem, powder X-ray diffraction reveals the variation in the crystal structure and crystallite size by means of annealing temperature. IR spectroscopy confirms the coordination of CTAB with the CdS nanoparticles. FESEM and TEM analyses were used to investigate the morphology, particle size and particle size distribution of the CdS nanoparticles. EDX analysis gives the elemental composition of the title compound. UV–Vis-NIR reflectance spectroscopy explains the absorption nature and band gap of CdS nanoparticles. Photoluminescence analysis gives out the luminescence behavior of the title compound and its variation with regarding to the annealing temperature. Herein, we conclude that, the particle size increases according to the increase in annealing temperature.

Influence of annealing temperature on structural, morphological and optical properties of CTAB assisted cadmium sulphide (CdS) quantum dots: promising candidate for quantum dot sensitized solar cell (QDSSC) applications

Synthesis and characterization of nano-crystalline silicon grown by atom beam sputtering technique are reported. Rapid thermal annealing of the deposited films is carried out in Ar + 5% H2 atmosphere for 5 min at different temperatures for precipitation of silicon nano-crystals. The samples are characterized for their optical and structural properties using various techniques. Structural studies are carried out by micro-Raman spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy (TEM), high resolution transmission electron microscopy, and selected area electron diffraction. The optical properties are studied by photoluminescence and UV-vis absorption spectroscopy, and bandgaps are evaluated. The bandgaps are found to decrease after rapid thermal treatment. The micro-Raman studies show the formation of nano-crystalline silicon in as-deposited as well as annealed films. The shifting and broadening in Raman peak suggest formation of nano-phase in the samples. Results of micro-Raman, photoluminescence, and TEM studies suggest the presence of a bimodal crystallite size distribution for the films annealed at higher temperatures. The results show that atom beam sputtering is a suitable technique to synthesize nearly mono-dispersed silicon nano-crystals. The size of the nano-crystals may be controlled by varying annealing parameters.

https://link.springer.com/content/pdf/10.1186%2F1556-276X-7-547.pdf

Debulal Kabiraj

Papers

Opto-structural studies of well-dispersed silicon nano-crystals grown by atom beam sputtering