Luminescence of Ca(NbO3)2:Pr3+: Pr3+ and self-trapped exciton emission

Photoluminescence and time resolved photoluminescence spectra of Ca(NbO3)2 doped with Pr3+, excited under 37,000 cm−1 (270 nm), obtained at high hydrostatic pressure up to 20 kbar applied in a sapphire anvil cells, are presented. At ambient conditions, the emission spectrum obtained in the time interval 0–1 μs is dominated by spin allowed transitions from the 3P0 state. The luminescence related to transitions from 1D2, characterized by a decay time equal to 33 μs, is observed when one excites directly the Pr3+ ion with 30,770 cm−1 (325 nm) wavelength. The introduction of Pr3+ impurities in Ca(NbO3)2 does not quench the self-trapped exciton (STE) luminescence. This luminescence, peaking at 20,000 cm−1 (500 nm), having a decay time of 61 ± 1 μs, still occurs when the crystal is excited with a wavelength of 37,000 cm−1 (270 nm) or shorter. Under such excitation a fraction of the STE luminescence is reabsorbed by Pr3+ ions; in this case the emission lifetime of the 1D2 → 3H4 transition of Pr3+ is 64 ± 3 μs. This effect is stable also at high pressure.