Luminescence of CaWO4:Pr3+ and CaWO4:Tb3+ at ambient and high hydrostatic pressures

Photoluminescence spectra of CaWO₄ doped with Pr³⁺ and Tb³⁺ obtained at high hydrostatic pressures up to 315 kbar applied in a diamond anvil cell (DAC) are presented. The intensities of the luminescence from the ³P₀ state of Pr³⁺ and from the ⁵D₃ state of Tb³⁺ decreased with increasing pressure. At pressures greater than 50 kbar, the ¹D₂ → ³H_J transitions in Pr³⁺ and the ⁵D₄ → ⁷F_J transitions in Tb³⁺ dominated the spectra. At pressures greater than 100 kbar, only emissions from the lower excited states were observed. At pressures greater than 150 kbar, luminescence from the ¹D₂ and ⁵D₄ states also decreased with increasing pressure, and at a pressure of 315 kbar for CaWO₄:Pr³⁺ and 190 kbar for CaWO₄:Tb³⁺, the emissions related to the Pr³⁺ and Tb³⁺ were quenched. These effects were related to the influence of impurity trapped excitons (ITEs) on the efficiency of the f–f emission in the Pr³⁺ and Tb³⁺ ions. Analysis of the emission spectra collected at different pressures allowed the energies of the ground states of the Pr³⁺ and Tb³⁺ ions with respect to the band edges of the CaWO₄ host to be estimated.