UV and electron radiation induced luminescence of Cu- and Eu doped lithium tetraborates

Complete text of publication follows. Cu and Eu doped borates exhibit very promising characteristics as laser hosts, scintillators, tissue-equivalent thermoluminescent (TL) detectors. For all these polyfunctional applications the doped borates interact with different kinds of radiation, and their luminescent properties are strongly determined by the nature of dopant and by the host-matrix state. Most of the publications concern the TL characterization, while photoluminescence (PhL) and radioluminescence (RL) studies are quite limited. Here we report the PhL and RL studies on Cu and Eu doped Li tetraborates (LTB) as dependent on dopant content and host: single crystal, polycrystalline, glassy. The main results, obtained in the study: LTB:Cu - PhL spectra of single crystals with different Cu content exhibited mono-band emission at 370 nm, excited by 250 nm for all samples. Luminescence intensity increased with increase of Cu content, so the luminescence quenching does not occur. It was revealed that the spectral patterns for PhL and RL are essentially the same, pointing to similar luminescent centres Cu1+ in both processes. The PhL spectra of single crystalline, polycrystalline and glassy modifications revealed the difference in their PhL intensities as well as in spectral pattern. LTB:Eu - It has been shown that polycrystalline and glassy samples exhibit practically the same PhL spectra, characteristic for Eu3+. The spectrum exhibited fine-structure line emission, dominated by 5D0 → 7F2 transition (peaked at 615 nm). High intensity ratio of the transition 5D0 → 7F2 to the 5D0 → F1 transition and the presence of 5D0 → 7F0 transition in the spectrum allow to assume very low site symmetry of Eu3+. The influence of ionizing radiation on the PhL intensity of these phosphors was revealed and discussed in the terms of changes in the valence state of the dopant and additional charge traps formation