K. Hamzah

A Model for Enhanced Up-Conversion Luminescence in Erbium-Doped Tellurite Glass Containing Silver Nanoparticles

Nanoparticles (NPs) size dependent enhancement of the infrared-to-visible frequency up-conversion (UC) and absorption coefficient in silver NPs embedded Er3+ doped tellurite glasses on pumping with the 976 nm radiation are investigated. Rate equations are derived by developing a comprehensive 4-level model in integrating the effects of quantum confinement and local field of silver NPs. Considering the spherical NPs size distribution as Gaussian, an analytical expression for the luminescence intensity and absorption coefficient are obtained for the first time. An enhancement in UC emission intensity of the green bands (2H11/2→4I15/2 and 4S3/2→4I15/2) and red band (4F9/2→4I15/2) emission of Er3+ ion at temperature 250 K and at optimized Er3+ concentration 1.0 mol% is observed up to few times in the presence of silver NPs. Furthermore, the green emission shows larger enhancement than the red emission. The observed of Er3+ luminescence is mainly attributed to the local field effects namely the surface plasmon resonance of silver NPs that causes an intensified electromagnetic field around NPs, resulting in enhanced optical transitions of Er3+ ions in the vicinity. The model is quite general and can be applied to other rare earth doped glasses containing metallic NPs. Our results on NPs size dependent emission intensity and absorption coefficient are in conformity with other findings. The present systematic study provides useful information for further development of UC lasers and sensors.

Luminescence from Silicon and Germanium Nanowires: A Phenomenological Model

The room temperature luminescence intensity as a function of the size and the voltage of silicon (Si) and germanium (Ge) nanowires (NWs) having 5 to 30 atoms per wire with diameter ranging from 1.2 nm to 3.5 nm are investigated. The effects of exciton energy states, localized surface states and the quantum confinement are integrated in our phenomenological model to derive an analytical expression for the photoluminescence (PL) and electroluminescence (EL) intensity. By controlling a set of fitting parameters in the model, one can tune the EL and PL peak and intensity. Our results show that both quantum confinement and surface passivation in addition to exciton effects determine the optical and electronic properties of Si and Ge NWs. We observed that the EL and PL intensities occurs at the same energy, however the EL intensity has sharp Gaussian sub peaks and red shifted compared to the PL intensity.

Optical Absorption of Erbium Doped Tellurite Glass

Improving the optical behavior of tellurite glass with controlled rare earth doping is an important issue from device perspectives. The Er3+ -doped tellurite glasses having composition (75-x)TeO2-20ZnO-5Na2O-xEr2O3 where (0 x 0.7) mol% are prepared by melt quenching technique and their structural and optical properties are investigated. Amorphous nature of the samples is confirmed through X-ray diffraction technique. The optical absorption recorded at room temperature in the wavelength range from 400 to 1000 nm exhibits five broad bands. The value of the optical band gap and the Urbach energy (ΔE) are calculated from the absorption edge data. The value of optical band gap lies between 2.18 eV and 2.89 eV for the indirect transition whereas the value of Urbach energy varies from 0.15 to 0.53 eV. The optical band gap and Urbach energy values are found to dependent strongly on the erbium concentration.

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...

Thermal and Photoluminescence Properties of Nd3+ Doped Tellurite Nanoglass

Series of glasses based on (75-x)TeO2-15MgO-10Na2O-xNd2O3, where x=0, 1.0, 2.0 and 3.0, are synthesized by conventional melt-quenching technique. The nanoglass particles are derived from heat treatment of this glass near crystallisation temperature for 3 hours. The existence of nanocrystalline nature of this glass is confirmed by x-ray diffraction (XRD) technique followed by calculation using Scherrer equation. Meanwhile, the crystallization temperature, Tc determined using Differential thermal analysis (DTA). The fluorescence spectra of Nd3+ ions exhibit emission transition of 2P3/24I9/2, 4G7/24I9/2, 2H11/24I9/2, and 4F9/24I9/2 under 765 nm excitation wavelengths.

Absorption Spectra of Neodymium Doped Tellurite Glass

Modifying the optical and structural properties of tellurite glasses by controlling rare earth doping is an important issue. Neodymium doped magnesium-tellurite glasses of composition TeO2-MgO-Na2O with concentration from 0.5 to 2.5 mol% were synthesized by conventional melt-quenching technique. The amorphous natures of the glass were confirmed from x-ray diffraction (XRD) pattern. The absorption spectra (exhibits five bands) were recorded to determine the optical energy gap and Urbach energy. The values of the optical band gap are found to lie between 3.04-3.20 eV, while the Urbach energy values varies are between 0.21-0.12 eV. The optical energy gap for indirect forbidden transition has increased whereas the values of Urbach energy have decreased with the increasing of Nd2O3 content. The structural and optical properties were found to be strongly affected by the varying concentration of Nd3+ ions.

Optical Properties of LiNbO3 Single Crystal Grown by Czochralski Method

Pure LiNbO3 single crystal was grown by Czochralski method using Automatic Diameter Control-Crystal Growth System (ADC-CGS). The transmission spectrum was determined by using Infrared Spectroscopy while the refractive index was determined using UV-Vis spectroscopy via the Sellmeier equation. The density was also measured using the Archimedes principle. It was found that the peak for the absorption vibrational spectrum for LiNbO3 crystal occurs at 801?cm-1, 672?cm-1, 639?cm-1 and 435?cm-1. The refractive index, ne was found to be 2.480 and the crystal density was around 4.64?g/cm3.

Optical Properties of LiNbO[sub 3] Single Crystal Grown by Czochralski Method

Pure LiNbO3 single crystal was grown by Czochralski method using Automatic Diameter Control-Crystal Growth System (ADC-CGS). The transmission spectrum was determined by using Infrared Spectroscopy while the refractive index was determined using UV-Vis spectroscopy via the Sellmeier equation. The density was also measured using the Archimedes principle. It was found that the peak for the absorption vibrational spectrum for LiNbO3 crystal occurs at 801?cm-1, 672?cm-1, 639?cm-1 and 435?cm-1. The refractive index, ne was found to be 2.480 and the crystal density was around 4.64?g/cm3.