Electron capture inPbWO4: Mo andPbWO4:Mo,La single crystals: ESR and TSL study

Abstract

Electron spin resonance ͑ESR͒, thermally stimulated luminescence ͑TSL͒ and electrical conductivity measurements were performed on Mo-and ͑Mo,La͒-doped PbWO 4 crystals in order to understand electron capture processes involving the Mo-based defects. A defect consisting of an electron localized around the ͑MoO 4 ͒ 2− complex ͑͑MoO 4 ͒ 3− center͒ was evidenced by ESR after UV illumination and studied in detail; the thermally activated detrapping of electrons from ͑MoO 4 ͒ 3− centers in the 200-250 K temperature region was described also by TSL measurements. Finally, in La-codoped samples, free electrons in the conduction band were found by both ESR and electrical conductivity experiments, unveiling a donor character of La 3+ impurity in the PWO lattice. Microscopical aspects of the energy storage processes and radiation resistance of the material are discussed.

Complex oxide scintillators: Material defects and scintillation performance

“…Noticeable suppression of oxygen vacancybased electron traps and free electrons in conduction band were reported due to La 3+ doping in PbWO 4 [36,37] and one can suggest similar mechanism also in CaWO 4 . As a consequence there will be very limited capacity of the Ladoped CaWO 4 to provide deep electron traps for the electrons created under ionizing radiation which can suppress the induced absorption phenomena.…”

Localized excitons and defects in PbWO4 single crystals: a luminescence and photo‐thermally stimulated disintegration study

“…In all oxygen-vacancy-rich crystals, the G(II) emission band (2.5 eV) strongly dominates in the TSL spectra in the 100-300 K temperature range. This is evident from the high-energy shift of the TSL spectrum with increasing temperature [23] as well as from the high-energy shift of the TSL spectrum with respect to the photoluminescence spectrum (see e.g. the inset in Fig.…”

“…It means that in the crystal studied, con-taining 800 ppm of Mo, the position of the MoO 4 3--related peak should be close to that observed in [32]. In [23] it was shown by the ESR method that thermal destruction of MoO 4 3-centers takes place around 245 K and the corresponding activation energy is 0.53 eV. The value E t = 0.51 ± 0.05 eV was calculated in [23] for the thermal depth of the trap related to the TSL peak observed in the mentioned paper at 243 K, and the value E t = 0.51 eV was extracted from the temperature dependence of conductivity in the La-co-doped PbWO 4 :Mo crystal.…”

“…The origin of hole centers in PbWO 4 crystals is not still clear as they are not detectable by the ESR method [23][24][25][26][27][28]. As the hole counterparts serve as recombination centers, the spectral position of the TSL spectrum in each TSL peak can give information on the origin of the related hole centers.…”

“…In [23] it was shown by the ESR method that thermal destruction of MoO 4 3-centers takes place around 245 K and the corresponding activation energy is 0.53 eV. The value E t = 0.51 ± 0.05 eV was calculated in [23] for the thermal depth of the trap related to the TSL peak observed in the mentioned paper at 243 K, and the value E t = 0.51 eV was extracted from the temperature dependence of conductivity in the La-co-doped PbWO 4 :Mo crystal. A very close value of E t (0.52 ± 0.02 eV) was obtained in the present paper for the TSL peak at 247 K. This peak is the only TSL peak in the crystal studied which is located in the temperature range characteristic for thermal decay of MoO 4 3-centers.…”