Jitender Jindal

Luminescence Properties of Eu2+/Eu3+ Activated Barium Aluminate Phosphors with Gd3+ Concentration Variation

BaAl2O4:Eu2+/Eu3+ (1 mol %) co-doped with varying concentrations of Gd3+ (1, 2, 5 and 10 mol%) were prepared by combustion synthesis method at 600°C. All the compositions were investigated for their structural and photoluminescence properties. Samples prepared in open atmosphere showed the presence of both Eu3+ and Eu2+ states which indicates the reduction of Eu3+ to Eu2+ during the preparation of these compounds. The prepared materials at 600°C showed high intense broad peaks around 498 nm corresponding to Eu2+ and small peaks in the red region which are attributed to the presence of Eu3+. In the 1000°C annealed compounds, the intensity of the peak at 498 nm got increased. The intensity of this broad band for BaAl2O4:Eu2+/Eu3+(1 mol%):Gd3+(1 mol%) was three times than that of BaAl2O4:Eu2+/Eu3+(1 mol%). Thus second rare earth ion (Gd3+) acted as a good sensitizer and enhanced the photoluminescence intensity. The XRD spectra revealed the presence of hexagonal phase of BaAl2O4 as main phase and a small amount of a mixed phase Ba O! 6.6 Al2O3. Doping of Eu3+, Gd3+ did not change the crystalline structure of barium aluminate (BaAl2O4).

Synthesis and Charcterization of Coupled ZnO/SnO2 Photocatalysts and Their Activity towards Degradation of Cibacron Red Dye

ABSTRACT A series of coupled ZnO-SnO2 photocatalyst was successfully synthesized in the Zn:Sn molar ratio of 20:1, 10:1, 5:1 and 2:1 via co-precipitation method followed by calcination at different temperatures. The synthesized materials were characterized by X-ray diffraction, diffuse reflectance spectra, scanning electron microscope and transmission electron microscope. Photocatalytic activitiy of synthesized materials was applied for the degradation of cibacron red dye in aqueous solution under UV-A light irradiation. Experimental results revealed that the coupled ZnO-SnO2 photocatalyst with Zn:Sn molar ratio 10:1, calcined at 600oC for 1 h was the most efficient photocatalyst among synthesized samples for the degradation of cibacron red. Superoxide anion radical (•O2–) was found to be the prominent active species responsible for degradation comparative to hole (h+), hydroxyl radical (•OH). GRAPHICAL ABSTRACT

Synthesis and characterization of nanoporous anodic oxide film on aluminum in H3PO4 + KMnO4 electrolyte mixture at different anodization conditions

The micro structural properties of nanoporous anodic oxide film formed in H3PO4 were highly influenced by addition of a low concentration of KMnO4 (0.0005 M) in 1 M H3PO4 solution. The KMnO4 as additive enhanced the growth rate of oxide film formation as well as thickness of pore walls. Furthermore the growth rate was found increased with increase in applied current density. The increase in temperature and lack of stirring during anodization causes the thinness of pore wall which leads to increase in pore volume. With the decrease in concentration of H3PO4 in anodizing electrolyte from 1M to 0.3 M, keeping all other conditions constant, the decrease in porosity was observed. This might be due to the dissolution of aluminium oxide film in highly concentrated acidic solution.

Structural and optical properties of Ta2O5:Eu3+: Mg2+ or Ca2+ phosphor prepared by molten salt method

Ta2O5:Eu3+: Mg2+ or Ca2+ phosphor materials were prepared by molten salt method using KCl as flux. The X-ray diffraction (XRD) patterns illustrated that the well crystallized Ta2O5:Eu3+: Mg2+ or Ca2+ were formed in the presence of flux under reduced temperature (800 °C) in contrast to conventional solid state method (1200-1500 °C). Scanning electron microscope (SEM) images indicate the achievement of well dispersed particles (hexagonal tablet and rod-like structures). Meanwhile, the photo-luminescent studies demonstrated that Ta2O5 is an efficient host to sensitize europium red emissions. The addition of Mg2+ or Ca2+ as co-dopant enhanced the luminescent intensity of Ta2O5: Eu3+ compound.