Photoluminescence and Scintillation Modulation Upon UV/X-ray-Induced Photochromism in Europium Tungstate Phosphors

Abstract

Rare earth (RE) tungstates with general formula REW2O6(OH)3 (RE = YIII or EuIII) were synthesized by hydrothermal method by using different citric acid contents. The prepared samples exhibit both UV and X-ray-induced photochromism at room temperature, as well as photomodulated luminescence. The presence of citric acid residues improves the photochromism when the samples are UV-irradiated, but has a secondary effect when the material is exposed to X-ray, evidencing particular mechanisms of action in each case. The emission profiles, in its turn, are similar independently of irradiation source. The continuous irradiation leads to color changes of samples concomitantly to the suppression of EuIII emission, without variations in the point symmetry of EuIII, but showing differences in the quenching behaviour according the excitation energy. The observed photochromic effect is stable and persists for several hours, which can be reversed by heating the irradiated material in air for a few minutes, when the restitution of emission intensity takes place. The observed properties make these materials promising for ionizing radiation detection and optical data storage.