Md. Supar Rohani

Synthesis and characterization of lithium niobium borate glasses containing neodymium

A series of (90– x )Li 2 B 4 O 7 -10Nb 2 O 5 - x Nd 2 O 3 glass samples ( x =0, 5 mol.%, 10 mol.%, 15 mol.%, 20 mol.% and 25 mol.%) were synthesized using melt quenching tec hnique. X-ray diffraction (XRD), differential thermal analyzer (DTA), Fourier transformed infrared (FTIR), ultraviolet-visible-near-infrared (UV-Vis-NIR) spectrometer and photoluminescence (PL) spectroscopic character i- zations were made to examine the influence of Nd 3+ concentration on the physical, structural and optical properties. Various physical properties such as glasses densit y, molar volume, thermal stability, ion concentration, polar on radius, inter-nuclear distance , field strength, cut-off wavelength, energy band gap and Urbach energy were calculated. Th e samples were amorphous in nature and con- firmed from XRD pattern. The FTIR spectra revealed the presence of BO 3 and BO 4 functional groups. UV-Vi s-NIR spectra exhibited nine prominent bands centered at 353, 430, 475, 524, 583, 681, 745, 803, 875 nm corresponding to the transitions from the groun d state to 4 D 3/2 , 2 P 1/2 , 2 G 9/2 , 4 G 7/2 , 4 G 5/2 , 4 F 9/2 , 4 F 7/2 , 4 F 5/2 , 4 F 3/2 excited states, respectively. Moreov er, the emission spectra at 355 nm ex- citation displayed three peaks centered at 903 nm ( 4 F 3/2 → 4 I 9/2 ), 1059 nm ( 4 F 3/2 → 4 I 11/2 ) and 1333 nm ( 4 F 3/2 → 4 I 13/2 ), respectively. Fluo- rescence lifetime was recorded between 53.69 to 28.43 μs. It was found that varying concentration of Nd 3+ ions strongly affected the physical, structural and optical properties of the glass samples.

Erbium concentration dependent absorbance in tellurite glass

Enhancing the optical absorption cross-section in topically important rare earth doped tellurite glasses is challenging for photonic devices. Controlled synthesis and detailed characterizations of the optical properties of these glasses are important for the optimization. The influence of varying concentration of Er3+ ions on the absorbance characteristics of lead tellurite glasses synthesized via melt-quenching technique are investigated. The UV-Vis absorption spectra exhibits six prominent peaks centered at 490, 526, 652, 800, 982 and 1520 nm ascribed to the transitions in erbium ion from the ground state to the excited states 4F7/2, 2H11/2, 4F9/2, 4I9/2, 2H11/2 and 4I13/2, respectively. The results are analyzed by means of optical band gap Eg and Urbach energy Eu. The values of the energy band gap are found decreased from 2.82 to 2.51 eV and the Urbach energy increased from 0.15 to 0.24 eV with the increase of the Er2O3 concentration from 0 to 1.5 mol%. The excellent absorbance of the prepared tellurit...

Dielectric Function of Silicon Nanoclusters: Role of Hydrogen

Electronic and optical properties of small silicon quantum dots having 3 to 44 atoms per dot with and without surface passivation are investigated by computer simulation using the pseudo-potential approach. An empirical pseudo-potential Hamiltonian, a plane-wave basis expansion and a basic tetrahedral structure with undistorted local bonding configurations are used. The structures of the quantum dots are relaxed and optimized before and after hydrogen passivation. It is found that the gap increases more for a hydrogenated surface than the unpassivated one. Thus, both quantum confinement and surface passivation determine the optical and electronic properties of Si quantum dots. Visible luminescence is probably due to the radiative recombination of electrons and holes in the quantum-confined nanostructures. The effect of passivation of the surface dangling bonds by hydrogen atoms and the role of surface states on the gap energy is also examined. The results for the density of states, the dielectric function, the frequency dependent optical absorption cross section, the extinction coefficient and the static dielectric constants of the size are presented. The importance of the confinement and the role of surface passivation on the optical effects are discussed.

Model Investigation of Temperature and Concentration Dependent Luminescence of Erbium-doped Tellurite Glasses

Improving the up‐conversion efficiency is the key issue in tellurite glasses. The quantum efficiency, radiative transition rate and lifetimes of excited states are greatly influenced by the optical properties of the host material, ligand field, multiphonon relaxation processes, impurities, temperature and concentration of erbium ions. We develop a comprehensive 4‐level model to examine the radiative and nonradiative (NR) decay processes for the green (4S3/2→4I15/2) and red (4F9/2→4I15/2) emission over a temperature range of (10–340 K) and concentration range of (0.1–4.5 mol.%). Concentration dependent enhancement and thermal quenching of efficiency for up‐conversion is investigated using the derived rate equations. These features are attributed to the NR energy transfer processes, trapped impurity effects, and thermal assisted hopping. The unusual nature of temperature and concentration dependent quenching effects for green and red emission is queries for further investigations. It is further suggested th...

Excitonic contribution of nanosilicon on light emitting properties

A phenomenological model is developed by integrating the effect of excitonic energy states, localized surface states and quantum confinement (QC) to obtain an analytical expression for the room temperature photoluminescence (PL) intensity. We calculate the binding energy of strongly confined excitons in silicon (Si) quantum dots (QD) having sizes 1 to 7.75 nm to examine its contribution on optical band gap and electronic properties. The band gap with excitonic contribution is found to decrease as much as 0.23 eV for the smallest dot. The effect of exciton states explains almost accurately the experimental PL data. Our model provides the mechanism for controlling the PL intensity through fitting parameters. Huge excitonic effects, which depend strongly on QD size and shape, characterize the optical spectra. The results for the size dependence of the optical band gap, the PL intensity, and oscillator strength are presented the role excitonic effects on optical and electronic properties are discussed.

Spectroscopic Properties of Er3+ Doped Phosphate Glass

A series of erbium doped phosphate glass has been successfully prepared using melt quenching technique. The glass density is decreased as the glass host content increases. The infrared absorption spectroscopy has been carried out to this series of glass. The samples exhibit five absorption bands in the range of 400–1400 cm−1. The peaks assigned to P=O(s), PO2(s), P–O−, P–O–P(s) and PO43−. Meanwhile, the luminescence spectroscopy shows the emission spectra of 2H9/2, 4F3/2, 4F7/2 and 4I9/2 at their transition level. The transition of 4F7/2 gives strong and weak emission peak.

Characterisation of Erbium Doped Phosphate Glass

A series of erbium doped phosphate glass has been successfully fabricated, and the determination of their density and luminescence properties has been carried out. It is particularly interesting to study the effect of modifying oxides to the properties of the glass. The glass density reduces with the increasing content of Na2O. The emission spectra from luminescence spectroscopy resolved six emission peaks from the excitation wavelength of 336.8 nm (3.69 eV). The emission of 4F7/2 gives two emission peaks, where the peak near 482 nm shows a higher intensity and the peak near 491 nm gives a weak emission spectra.

The Growth and Growth Mechanism of Nd:YAG Single Crystals By Czochralski Method

Growth of Nd:YAG single crystals by the Czochralski method in an argon atmosphere with ADC (Automatic Diameter Control) r.f. heating was investigated. The conditions required to grow Nd:YAG single crystals are described. The relationship of the latter to the growth mechanism is discussed and a mechanism proposed which provides an explanation of the manner in which the crystals grow and reject impurities. The Nd:YAG single crystal with growth direction of 〈111〉 was produced by effective control of growth conditions.