Structural and optical characteristics of α-Bi2O3/ Bi2O(3-x):Ho3+ thin films deposited by pulsed laser deposition for improved green and near-infrared emissions and photocatalytic activity.

Pulsed laser deposited films on glass substrate deposited at different substrate temperatures (Ts) and partial pressures of oxygen, Ho3+-doped Bi2O3 films were produced. The degradation capability of the Rhodamine B dye using the Bi2O3:Ho3+ films was explored. The impact of the Bi2O3:Ho3+ content on the dye degradation performance was analyzed. The X-ray powder diffraction patterns showed that the films deposited at 400 °C had an α-Bi2O3 phase. The impacts of various Ts and O2 partial pressures were correlated with the surface morphology and the thickness of the films using results of field emission scanning electron microscope. The thin films deposited at a low O2 partial pressure of 5-20 mTorr at Ts = 400 °C exhibited nano-needles with an average size of 80 nm and a length of ∼750 nm. The estimated band gap of the prepared films was found to vary between 2.6 and 3.0 eV. The photoluminescence (PL) of the Bi2O3:Ho3+ thin films excited at 450 nm showed an intense green band emission observed at 548 nm, and the feeble emissions at 654 and 753 nm were ascribed to the transitions of Ho3+. The nano-needle particles of the α-Bi2O3:Ho3+ exhibited a maximum PL intensity for the 20 mTorr O2 partial pressure thin film. The films prepared in vacuum and with an O2 partial pressure of 5 mTorr exhibited a 41 % dye degradation efficiency during a duration of 270 min of the photocatalysis experiment.

Role of Li+ ions on the surface morphology and thermoluminescence properties of Y2 O3 :Tm3+ nanophosphor.

Y2 O3 :Tm3+ and Li+ co-doped Y2 O3 :Tm3+ nanopowders were synthesized using the solution combustion method for possible application in ultraviolet (UV) light dosimetry. X-ray diffraction revealed the crystallite sizes to be in the range 21-44 nm and 30-121 nm using the Scherrer equation and the W-H plot relationship, respectively. Field emission scanning electron microscopy confirmed that, after co-doping with 4 mol% concentration of Li+ , the particles were spherical in nature with an average size of ~30 nm. Fourier transformed infrared spectroscopy results showed bands at wavenumbers of 556, 1499, 1704, 2342, 2358, 2973, 3433, and 3610 cm-1 that corresponded to the stretching and bending vibrations of Y-O, C=O and O-H. Thermoluminescence (TL) glow peaks for Y2 O3 :Tm3+ nanophosphors observed at 399 and 590 K were attributed to oxygen defects caused using UV irradiation. These oxygen defects firstly resulted in an increased prominent peak TL intensity for up to 270 min of irradiation and then a decrease. This was attributed to the presence of oxygen defect clusters that caused a reduction in recombination centres. The Li+ co-doped sample showed peaks at 356, 430, and 583 K and its intensity sublinearly increased up to 90 min and then thereafter decreased. The TL trapping parameters were calculated using computerized glow curve deconvolution methods. The Li+ co-doped sample exhibited less fading and high trap density under the UV radiation.

Synthesis characterization and luminescence studies of gamma irradiated nanocrystalline yttrium oxide.

Nanocrystalline Y2O3 is synthesized by solution combustion technique using urea and glycine as fuels. X-ray diffraction (XRD) pattern of as prepared sample shows amorphous nature while annealed samples show cubic nature. The average crystallite size is calculated using Scherrer's formula and is found to be in the range 14-30 nm for samples synthesized using urea and 15-20 nm for samples synthesized using glycine respectively. Field emission scanning electron microscopy (FE-SEM) image of 1173 K annealed Y2O3 samples show well separated spherical shape particles and the average particle size is found to be in the range 28-35 nm. Fourier transformed infrared (FTIR) and Raman spectroscopy reveals a stretching of Y-O bond. Electron spin resonance (ESR) shows V(-) center, O2(-) and Y(2+) defects. A broad photoluminescence (PL) emission with peak at ~386nm is observed when the sample is excited with 252 nm. Thermoluminescence (TL) properties of γ-irradiated Y2O3 nanopowder are studied at a heating rate of 5 K s(-1). The samples prepared by using urea show a prominent and well resolved peak at ~383 K and a weak one at ~570 K. It is also found that TL glow peak intensity (I(m1)) at ~383 K increases with increase in γ-dose up to ~6.0 kGy and then decreases with increase in dose. However, glycine used Y2O3 shows a prominent TL glow with peaks at 396 K and 590 K. Among the fuels, urea used Y2O3 shows simple and well resolved TL glows. This might be due to fuel and hence particle size effect. The kinetic parameters are calculated by Chen's glow curve peak shape method and results are discussed in detail.