Chirantan Dey

Bio: Chirantan Dey is an academic researcher from Central Glass and Ceramic Research Institute. The author has contributed to research in topics: Photoluminescence & Absorption spectroscopy. The author has an hindex of 5, co-authored 11 publications receiving 110 citations.

Thermal, Structural, and Enhanced Photoluminescence Properties of Eu3+-doped Transparent Willemite Glass–Ceramic Nanocomposites

Abstract: The precursor glass in the ZnO–Al2O3–B2O3–SiO2 (ZABS) system doped with Eu2O3 was prepared by the melt-quench technique. The transparent willemite, Zn2SiO4 (ZS) glass–ceramic nanocomposites were derived from this precursor glass by a controlled crystallization process. The formation of willemite crystal phase, size, and morphology with increase in heat-treatment time was examined by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) techniques. The average calculated crystallite size obtained from XRD is found to be in the range 18–70 nm whereas the grain size observed in FESEM is 50–250 nm. The refractive index value is decreased with increase in heat-treatment time which is caused by the partial replacement of ZnO4 units of ZS nanocrystals by AlO4 units due to generation of vacancies. Fourier transform infrared (FTIR) reflection spectroscopy was used to evaluate its structural evolution. Vickers hardness study indicates marked improvement of hardness in the resultant glass-ceramics compared with its precursor glass. The photoluminescence spectra of Eu3+ ions exhibit emission transitions of 5D0→7Fj (j = 0, 1, 2, 3, and 4) and its excitation spectra show an intense absorption band at 395 nm. These spectra reveal that the luminescence performance of the glass–ceramic nanocomposites is enhanced up to 17-fold with the process of heat treatment. This enhancement is caused by partitioning of Eu3+ ions into glassy phase instead of into the willemite crystals with progress of heat treatment. Such luminescent glass–ceramic nanocomposites are expected to find potential applications in solid-state red lasers, phosphors, and optical display systems.

Synthesis and optical properties of multifunctional CdS nanostructured dielectric nanocomposites

Abstract: Highly luminescent CdS nanocrystals (NCs) grown in a dielectric (borosilicate glass) matrix have been synthesized by the melt quenching technique. NC sizes are varied by controlling the post thermal treatment durations in the glass matrix and their optical properties have been investigated. The sizes of the CdS NCs calculated from the transmission electron microscopic (TEM) images are found to alter in the range of 4–40 nm. Field emission scanning electron microscopic (FESEM) images reveal the presence of 30–100 nm CdS nanostructures. Photoluminescence (PL) of CdS–glass nanocomposites reveals a sharp green emission peak (∼508 nm) due to direct electron–hole recombination along with a broad trap-related emission band. The sharpness, tuning ability of the absorption spectra, and PL covering the visible spectral range are the highest reported to date for any compound semiconductor–dielectric nanocomposite and one single nanocomposite, synthesized by this method, advocating for their potential utilization as functional materials in the fabrication of multiple devices such as luminescent solar concentrators (LSCs), optical color filters, and solid-state lasers.

White light emitting Ho3+-doped CdS nanocrystal ingrained glass nanocomposites

Abstract: We report the generation of white light from Ho3+ ion doped CdS nanocrystal ingrained borosilicate glass nanocomposites prepared by the conventional melt-quench method. Near visible 405 nm diode laser excited white light emission is produced by tuning the blue emission from the Ho3+ ions, green band edge, and orange-red surface-state emissions of the nanocrystalline CdS, which are further controlled by the size of the nanocrystals. The absorption and emission spectra evidenced the excitation of Ho3+ ions by absorption of photons emitted by the CdS nanocrystals. The high color rendering index (CRI = 84–89) and befitting chromaticity coordinates (x = 0.308–0.309, y = 0.326–0.338) of white light emission, near visible harmless excitation wavelength (405 nm), and high absorbance values at excitation wavelength point out that these glass nanocomposites may serve as a prominent candidate for resin free high power white light emitting diodes.

Single-step in-situ synthesis and optical properties of ZnSe nanostructured dielectric nanocomposites

Abstract: This work provides the evidence of visible red photoluminescent light emission from ZnSe nanocrystals (NCs) grown within a dielectric (borosilicate glass) matrix synthesized by a single step in-situ technique for the first time and the NC sizes were controlled by varying only the concentration of ZnSe in glass matrix. The ZnSe NCs were investigated by UV-Vis optical absorption spectroscopy, Raman spectroscopy, and transmission electron microscopy (TEM). The sizes of the ZnSe NCs estimated from the TEM images are found to alter in the range of 2–53 nm. Their smaller sizes of the NCs were also calculated by using the optical absorption spectra and the effective mass approximation model. The band gap enlargements both for carrier and exciton confinements were evaluated and found to be changed in the range of 0–1.0 eV. The Raman spectroscopic studies showed blue shifted Raman peaks of ZnSe at 295 and 315 cm−1 indicating phonon confinement effect as well as compressive stress effect on the surface atoms of the NCs. Red photoluminescence in ZnSe-glass nanocomposite reveals a broad multiple-peak structure due to overlapping of emission from NC size related electron-hole recombination (∼707 nm) and emissions from defects to traps, which were formed due to Se and Zn vacancies signifying potential application in photonics.

Photochemistry of colloidal metal sulfides. 7. Absorption and fluorescence of extremely small ZnS particles (The world of the neglected dimensions)

Abstract: Extremely small colloidal ZnS particles (diameter -1.7 nm) were made by either photo-degradation of 3 nm particles or rapid precipitation in phosphate containing solution at pH = 7-8. The absorption spectra of these particles are different from that of macrocrystalline ZnS, and the changes are regarded as an indication for the transition from semiconductor ZnS to polymolecular ZnS with decreasing particle size. - The dependence of the intensity of the fluorescence on particle size, temperature, photoanodic corrosion and the quenching of fluorescence were investigated for colloids on a silicon dioxide carrier, in phosphate solution, and without a stabilizer. Photo-anodic corrosion strongly improves the fluorescence properties. - One adsorbed Cd 2+ ion per colloidal particle is sufficient for efficient quenching of the fluorescence. However, a new fluorescence band appears which is explained by the formation of a layer of 1:1 co-colloid at the surface of the ZnS particles. - Methylviologen was also found to be a very efficient quencher. The decay of the fluorescence is wavelength dependent, i.e. the fraction of long-lived fluorescence is greater at longer wavelengths. - A mechanism is discussed, where the fluorescence centers are anion vacancies, and fluorescence is emitted when electrons trapped in states of different energies and exhibiting different life-times tunnel to the localized positive holes.

ZnS nanostructures: From synthesis to applications

Abstract: Zinc sulfide (ZnS) is one of the first semiconductors discovered. It has traditionally shown remarkable versatility and promise for novel fundamental properties and diverse applications. The nanoscale morphologies of ZnS have been proven to be one of the richest among all inorganic semiconductors. In this article, we provide a comprehensive review of the state-of-the-art research activities related to ZnS nanostructures. We begin with a historical background of ZnS, description of its structure, chemical and electronic properties, and its unique advantages in specific potential applications. This is followed by in-detail discussions on the recent progress in the synthesis, analysis of novel properties and potential applications, with the focus on the critical experiments determining the electrical, chemical and physical parameters of the nanostructures, and the interplay between synthetic conditions and nanoscale morphologies. Finally, we highlight the recent achievements regarding the improvement of ZnS novel properties and finding prospective applications, such as field emitters, field effect transistors (FETs), p-type conductors, catalyzators, UV-light sensors, chemical sensors (including gas sensors), biosensors, and nanogenerators. Overall this review presents a systematic investigation of the ‘synthesis-property-application’ triangle for the diverse ZnS nanostructures.

Structural and emission properties of Eu3+-doped alkaline earth zinc-phosphate glasses for white LED applications

Abstract: Quaternary alkaline earth zinc-phosphate glasses in molar composition (40 − x)ZnO – 35P2O5 – 20RO – 5TiO2 – xEu2O3 (where x=1 and R=Mg, Ca, Sr, and Ba) were prepared by melt quenching technique. These glasses were studied with respect to their thermal, structural, and photoluminescent properties. The maximum value of the glass transition temperature (Tg) was observed for BaO network modifier mixed glass and minimum was observed for MgO network modifier glass. All the glasses were found to be amorphous in nature. The FT-IR suggested the glasses to be in pyrophosphate structure, which matches with the theoretical estimation of O/P atomic ratio and the maximum depolymerization was observed for glass mixed with BaO network modifier. The intense emission peak was observed at 613 nm (5D0→7F2) under excitation of 392 nm, which matches well with excitation of commercial n-UV LED chips. The highest emission intensity and quantum efficiency was observed for the glass mixed with BaO network modifier. Based on these results, another set of glass samples was prepared with molar composition (40 − x)ZnO – 35P2O5 – 20BaO – 5TiO2 – xEu2O3 (x=3, 5, 7, and 9) to investigate the optimized emission intensity in these glasses. The glasses exhibited crystalline features along with amorphous nature and a drastic variation in asymmetric ratio at higher concentration (7 and 9 mol%) of Eu2O3. The color of emission also shifted from red to reddish orange with increase in the concentration of Eu2O3. These glasses are potential candidates to use as a red photoluminsecent component in the field of solid-state lighting devices.