Luminescence and stability of Tb doped CaF₂ nanoparticles

Luminescence properties of CaF₂:Tb³⁺ nanoparticles were studied in order to investigate the effect of CaF₂ native defects on the photoluminescence dynamics of Tb³⁺ ions. Incorporation of Tb ions into the CaF₂ host was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. Cross-relaxation energy transfer was observed from the photoluminescence spectra and decay curves upon excitation at 257 nm. However, the unusual long lifetime of the Tb³⁺ ion as well as the decreasing trend of emission lifetime of the ⁵D₃ level suggested the involvement of traps, which were further investigated by using temperature-dependent photoluminescence measurements, thermoluminescence and lifetime measurements at different wavelengths. This work highlights the critical role that the CaF₂ native defects play in the photoluminescence dynamics of Tb³⁺ ions incorporated in a CaF₂ matrix. The sample doped with 10 mol% of Tb³⁺ ions was found to be stable under prolonged 254 nm ultraviolet irradiation.