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In this work, a modified sonication induced wet chemical approach is adopted to synthesize highly luminescent and water soluble Cadmium Telluride (CdTe) quantum dots (QDs). Cadmium Chloride and Sodium Tellurite are used as the source of Cadmium and Tellurium. To limit the size of the QDs, Mercaptosuccinic acid is used as a capping agent. The refluxing time dependence on morphology, size, crystal structural, and optical properties of CdTe QDs are investigated. The refluxing time-dependent optical constants viz. band gap energy and Urbach energy of the QDs are estimated from UV-Vis absorption spectra. The fluorescence spectra of the QDs are also investigated by recording the spectra under the excitation wavelength at 320 nm. CdTe QDs are found to uniform in size. The average size of the QDs estimated from the HRTEM image analysis is about 5.8 nm and 8.2 nm for refluxing times 1 and 4 hours, respectively. The growth mechanism of the QDs as a function of refluxing time has also been discussed. Two phases of the CdTe QDs, namely hexagonal and cubic are confirmed from the HRTEM images and SAED patterns analysis. The phase transformation from hexagonal to cubic is successfully achieved by tuning the refluxing time from 1 to 4 hours.

This paper describes the preparation and characterization of nanocrystalline CdxPb1−xS thin films by chemical bath deposition method with different Pb and Cd solute ratios. XRD, HRTEM and SAED patterns show the nanocrystalline nature of films with the co-existence of cubic, hexagonal and tetragonal phases, while micro-Raman spectra reveals the presence of cubic and hexagonal phases in the films. The average crystallite size of CdxPb1−xS estimated from TEM and XRD methods were nearly same. The chemical bonding present in the films was studied by FTIR spectral analysis. SEM images show uniformly distributed grains of different sizes over the substrates. Optical studies show the prominent blue shift in band gap energy (Eg) with the increase in Cd content in PbS. The increment of Cd addition to CdxPb1−xS has led to enhance the transmittance as well as band gap energy.

In this paper, the influence of thickness and post deposition annealing temperature on thermally evaporated molybdenum oxide films has been studied. The X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) are used for crystal structural and surface morphological characterization of the films, respectively. The XRD analysis showed that the presence of α-MoO3 and MoO2 crystalline phase of the films annealed at elevated temperature ~ 250 °C after deposition. The optical constants are determined from UV–Vis transmission spectra. The optical band gap and Urbach energy is found to be temperature dependent. The refractive index of the films is estimated by the optical method as well as cross-sectional SEM image analysis. It is found that the refractive index of the films increases from ~ 1.70 to 2.03 with the decrease in film thickness from ~ 2.9 to 1.7 µm. It is also observed that the refractive index decreased from ~ 2.03 to 1.61 with the increase in post deposition annealing temperature from room temperature (RT) to ~ 250 °C. Moreover, extinction coefficient, optical conductivity, porosity, and film density are investigated as a function of source-substrate distance and post deposition annealing temperature. The Photoluminescence (PL) properties of the films are also investigated by recording spectra under the excitation wavelength at 250 nm.

Face recognition plays an important role in the field of biometrics. Detecting a face from a video or an image is a very popular topic in biometric research. The wide applications of face recognition in the real world are security systems, video surveillance, interaction of human and computer, and many more. Many algorithms have been developed so far and its proficiency has been on the forefront of research from the past two decades. This paper attempts to review the methods like PCA, LDA, CNN, SVM for face detection and on the various hybrid combinations of these techniques to deal with the challenges of face recognition. In addition, illuminations, pose variations, aging, and facial expressions have been discussed.

In this paper, the dispersion parameters of Molybdenum Oxide thin films viz: oscillator energy, dispersion energy, transition moments, static refractive index, oscillator strength, and oscillator wavelength are estimated via Wemple–DiDomenico (WDD) single oscillator model. The crystal structural, surface morphological, and optical transmission properties of Molybdenum Oxide thin films are also investigated so as to extract vital in-put parameters for WDD model. The X-ray Diffraction and Fourier Transform of Infrared analysis confirm that the film fabricated at substrate temperature ~ 300 °C under goes a successful dual phase transformation from amorphous to α- and β-MoO3 crystalline phase. Static refractive indices of the films are found to be vary from ~ 1.84 to 2.04 with the increase of substrate temperature during the thin film growth process via thermal evaporation technique. Moreover, the optical constants viz: film density, porosity, absorption coefficient, optical band gap, Urbach energy, steepness parameter, and strength of electron–phonon interaction are also studied as a function of substrate temperature. This is to establish a correlation between optical constants and dispersion parameters in the present paper.

In this paper, a modified top-down method is adopted to synthesize highly stable and water-soluble Molybdenum trioxide quantum dots (MoO3 QDs) without any surfactants. In this sonication induced modified method, commercial Molybdenum Oxide powder and Hydrochloric acid were used as the precursor and etchant, respectively. The impact of sonication bath temperature on the morphological, microstructural, size, crystal-structural, and optical properties of MoO3 QDs have been systematically investigated. The controlled sonication bath temperature during the synthesis process results in the tunability of the QDs. The mechanism behind the controlled size of the QDs deeply rooted in the acoustic cavitation phenomenon. The synthesized QDs exhibit poly-crystallinity with mixed phases: orthorhombic (α-MoO3) and hexagonal (h-MoO3). Interestingly, the complete elimination of the hexagonal phase from the QDs has been observed as a function of sonication bath temperature.

A simple and modified top-down approach to synthesize molybdenum oxide (MoOx: x = 2, 3) quantum dots (QDs) is proposed in this study. This modified approach involves the conversion of a bulk powder material into thin films followed by a sonication induced chemical etching process for synthesising QDs. X-Ray Diffraction (XRD) is used for crystal structural characterization of MoOx thin films. The crystal structure properties of the MoOx QDs are analysed by High Resolution Transmission Electron Microscopy (HRTEM) images and corresponding Selected Area Electron Diffraction (SAED) patterns. The optical band gap is estimated by Tauc's plot from UV-Vis-NIR absorption spectra. The excitation dependent photoluminescence (PL) emission of MoOx QDs as a function of acid concentration is investigated. The growth mechanism of QDs in different crystalline phases as a function of acid concentration is also exemplified in this work. The micro-Raman and Fourier Transform of Infrared (FTIR) spectra are recorded to analyse the vibrational spectrum of the molybdenum–oxygen (Mo–O) bonds in the MoOx QDs.