Five different types of spontaneous emission simultaneously observed in Tm2+ doped CsCaBr3

CsCaBr3 doped with 1% Tm2+ exhibits a rich emission spectrum at 10 K. Five emission bands are identified and characterised: a sharp and long-lived 4f–4f emission at 8796 cm−1. Broad 5d–4f emission bands from the lowest energy (5d)1(4f)12 configurations to the groundstate at 13 640 cm−1 (‘spin-allowed’) and 12 240 cm−1 (‘spin-forbidden’). Two broad emission bands from a higher-energy f–d state, one centered at 19 115 cm−1 to the 2F7/2 groundstate and the other one at 10 400 cm−1 to the first excited 2F5/2 state. The transitions are identified and the competition between radiative and nonradiative processes characterised from lifetime and temperature dependent measurements.