Judith Grimm and Hans U. Güdel
Five different types of spontaneous emission simultaneously observed in Tm²⁺ doped CsCaBr₃
Chem. Phys. Lett. 404, 40-43 (2005)                 

Abstract: 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 ²F_7/2 groundstate and the other one at 10 400 cm⁻¹ to the first excited ²F_5/2 state. The transitions are identified and the competition between radiative and nonradiative processes characterised from lifetime and temperature dependent measurements.