A.R. Dhobale

Optical properties of ammonium uranyl fluoride characterized by photoluminescence and photoacoustic spectroscopy.

PL and PAS studies were performed on uranyl compounds viz. uranium oxalate, uranium fluoride and ammonium uranyl fluoride. PL and PAS spectrum of ammonium uranyl fluoride is being reported for the first time. Ammonium uranyl fluoride is blue shifted with respect to uranyl fluoride, as a result of ammonium bonding. The vibronic separations were determined in the excited state and the ground state using excitation/PA spectra and emission spectra respectively. Fluorescence decay data could be fitted only with biexponential decay in all of these compounds indicating the presence of two different environments in these compounds. Low temperature luminescence leads to enhancement in emission intensity and lifetime value. The temperature dependence studies of average fluorescence lifetimes of ammonium uranyl are described in this paper. Based on this studies activation energy value for ammonium uranyl fluoride at which (3)∏ and (1)Σ potential surfaces will cross is calculated.

Photoinduced changes in photorefractive PVA films doped with Cr3+ and VO2+: EPR and PAS investigations

In order to understand the mechanism of optical image storage in photorefractive polyvinyl alcohol (PVA) films, photo-EPR and photoacoustic spectral investigations were carried out on PVA films doped with Cr3+ and VO2+. The EPR spectrum of Cr3+ has shown reduction in intensity onin situ illumination with copper vapor laser (CVL). The decay and recovery of Cr3+ signal, with and without CVL illumination respectively, was monitored at different temperatures in 10–300 K region. These were found to obey a double exponential, with one time constant independent of temperature, and the other showing significant temperature dependence. From Τ(T), activation energy for the charge carrier transport in one of the processes was estimated to be 0.016 eV. The PA spectra showed shift towards lower wavelength side on consecutive runs. On the other hand, VO2+ doped PVA film has not shown any significant changes in intensity on laser illumination. These observations suggest (i) interaction of PVA matrix with excited Cr3+ and (ii) predominant non-radiative relaxation in VO2+: PVA system with no change in the oxidation state.

Internal irradiation effects in239Pu doped K2Ca2(SO4)3): EPR, TSL and PAS investigations

The electron/hole trapped centres created during internal irradiation in239Pu doped K2Ca2(SO4)3 were investigated using electron paramagnetic resonance (EPR), thermally stimulated luminescence (TSL) and photoacoustic spectroscopic studies (PAS). These techniques were used to identify the defects and characterize the thermally induced relaxation processes. TSL studies of self (α)/γ-irradiated239Pu doped K2Ca2(SO4)3 revealed two glow peaks around 400 and 433K. Plutonium introduced as Pu4+ was partly reduced to Pu3+ due to self irradiation. This was ascertained from PAS studies. EPR studies carried out on these samples showed the formation of radical ions SO4−, SO3−, O3−, etc. The thermal destruction of SO4− ion was found to be associated with the prominent glow peak around 433K. Pu3+ was found to act as luminescent centre for the observed TSL glow. The trap depth for the glow peak at 433K has been determined from TSL and EPR data.

Photoacoustic spectroscopic and electron paramagnetic resonance investigations on copper doped alkali borosilicate glasses

Photoacoustic absorption (PA) spectroscopic and electron paramagnetic resonance (EPR) studies were carried out on 2.5% copper doped sodium-barium borosilicate glasses. It was found that the Jahn-Teller distorted Cu2+ species was present in a distorted octahedron with elongated z axis with the unpaired electron in dx2–y2 orbital. From the Hamiltonian parameters of EPR, Fermi contact term and dipolar terms were evaluated. By correlation of the PA data and EPR data, orbital reduction factors and bonding parameters were evaluated for the ion. The bonding parameters suggested the presence of covalency in the metal ligand bond in the glassy system.

Electron paramagnetic resonance, photo-acoustic spectroscopy and thermally stimulated luminescence for identification of thermally stimulated processes in gamma-irradiated LaBa2F7

Thermally stimulated luminescence (TSL), electron paramagnetic resonance (EPR) and photo-acoustic spectroscopy (PAS) techniques were used to investigate the radiation induced centers in polycrystalline LaBa2F7 containing trace amounts of other rare-earths particularly Gd3+ and Sm3+. The TSL glow curve of LaBa2F7 after g-irradiation to a dose of 3 kGy had shown a weak TSL glow peak at 390 K and a much stronger one at 495 K. The EPR spectra of the g-irradiated LaBa2F7 samples showed the presence of O- and O2- ions. Temperature dependence study of the EPR spectra showed that the thermal destruction of O- ion occurs in the 460-490 K temperature range. In g-irradiated samples, O- and F-centers were identified by PAS. The correlation of EPR and PAS results indicate that the prominent TSL glow at 495 K is associated with the thermal destruction of O- radical ion. The trap parameters viz. trap depth and frequency factor have been determined from TSL data.

Photoacoustic cell with black absorber as a detector for spectrophotometric studies

The PAS cell with carbon black absorber is used as a detector for spectrophotometry in an open room. This has immense potential of obtaining absorption speciation information from remote samples.