V. Natarajan

On the unusual photoluminescence of Eu3+ in α-Zn2P2O7: a time resolved emission spectrometric and Judd–Ofelt study

Zn2P2O7:Eu3+ was synthesized and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM); Fourier transformed infrared spectroscopy (FTIR) and photoluminescence (PL) techniques. Based on the time resolved emission spectroscopic investigations (TRES), it was inferred that two different types of Eu3+ ions were present in the zinc pyrophosphate. The first type was a long lived species (∼τ = 1.77 ms) present at relatively few symmetric ‘5-coordinated Zn’ sites, while the second was a short lived species (∼τ = 620 μs) present at symmetric ‘6-coordinated Zn’ sites. This unusual behavior of the trivalent rare earth species could be explained with the help of Judd–Ofelt (J–O) calculations. From the calculations, the radiative (τR) and non radiative (τNR) life times were evaluated for both species. It was observed that the radiative life time of the Eu3+ species present in symmetric environment was higher than that of the species present in the asymmetric environment, which is consistent with the selection rules governing the transition. It was observed that the presence of a very strong non-radiative component at the symmetric site brings down the overall lifetime value. The J–O intensity parameters for all the Eu3+ species present in the pyrophosphate system were calculated adopting standard procedure. Ω4 > Ω2 was found that for short lived species; while for the long lived species, the reverse trend was observed further confirming the correlation between the asymmetry and bonding.

SO4−–SO3− radical pair formation in Ce doped and Ce, U co-doped K3Na(SO4)2: EPR evidence and its role in TSL

Abstract Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) studies were carried out on cerium doped and cerium–uranium co-doped K 3 Na(SO 4 ) 2 samples after γ -irradiation. Three glow peaks around 352, 415 and 475 K were observed and their spectral characteristics have shown that Ce 3+ and UO 2 2+ act as the emission centres in K 3 Na(SO 4 ) 2 :Ce and K 3 Na(SO 4 ) 2 :Ce, U, respectively. In Ce–U co-doped sample, energy transfer from cerium to uranium takes place. The commonly occurring radiation-induced centres in sulphates, viz SO 3 − and SO 4 − were observed by EPR and SO 4 − radical ion was found to take part in the TSL emission at 415 K . The hitherto unknown information, however, is the formation of SO 4 − –SO 3 − radical pair creating deep traps in these lattices, apparently assisted by the dopants. This is the first observation of such radical pair formation leading to the identification of deep traps in this lattice. The radical pair, (SO 3 − –SO 4 − ) which is stable up to 970 K , decreases the intensity of the peak at 415 K due to the depletion of SO 4 − centres.

Thermally stimulated luminescence and electron paramagnetic resonance studies of doped K3Na(SO4)2

Abstract Rare earth and actinide doped alkali and alkaline earth sulphates, exhibit a variety of point defects stabilized due to the charge imbalance/self-irradiation and they play an important role in luminescence properties. In this paper, we report the point defects formed in the mixed sulphate K3Na(SO4)2 on doping with the radio-active rare earth element 147 Pm as studied by TSL and EPR techniques. EPR studies on self and gamma irradiated samples showed the signal due to the radical pair, SO4−–SO3− in addition to the signals from SO4−, SO3− and O2− ions. However EPR spectra of electron beam irradiated (undoped) K3Na(SO4)2 samples did not show the presence of the radical pair SO4−–SO3−, indicating the importance of dopant per se, in stabilizing the radical pair. EPR studies of 147 Pm doped samples annealed at different temperatures after gamma irradiation showed that SO4−–SO3− radical pair gets destroyed around 550 K , whereas SO4− ion gets annealed in the temperature range 375– 450 K . SO3− ion was found to be stable upto 600 K . From TSL–EPR correlation, it is inferred that the release of trapped hole at SO4− ion on heating leads to the formation of SO 4 2− ∗ and energy transfer to Pm3+ ion, results in the glow peak at 415 K .

Trace level determination of precious metals in aqueous medium, U, Th and Zr based nuclear materials by ICP-AES and EDXRF: a comparative study

An ICP-AES based method was developed for the direct determination of precious metals without any chemical/physical separation in nuclear materials and it was found to be simple, sensitive, less time consuming, no organic waste generation and no need of selective extraction. Analytical performance including detection limits, sensitivity, linear dynamic range, precession of different analytical lines of these elements was studied alongwith the spectral interference of U, Th and Zr to choose the best analytical lines. EDXRF method was used for comparison purpose.

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.

Speciation of uranium in solids using time resolved photoluminescence technique

A comprehensive study regarding the speciation of uranium in five different solids, namely, YBO3, Sr2P2O7, SrB4O7, SrBPO5 and SrZrO3 is presented using time resolved photoluminescence spectroscopy. The ‘Sr’ based hosts are considered as potential phosphor materials where as the borate based matrices are known to have near tissue equivalent absorption coefficients making them potential candidates for dosimetric applications. It was observed that, in case of the pyrophosphate, borophosphate and yttrium borate matrices, uranium gets stabilized as uranyl (

Nitrate anion effects on the trap formation and thermally stimulated luminescence of Np4+-doped BaCO3

{text{UO}}_{2}^{2 + }

EPR and ENDOR studies of self(α)-irradiation effects in Pu(VI) oxalate: evidence for participation of 5f electrons of 239Pu in chemical bonding with CO2−

UO22+), whereas, in case of the tetraborate and zirconate matrices, it was the uranate species,