Ultraviolet emission and unusual hot bands of Ho3+ in elpasolite hosts

The luminescence of Cs2NaHoCl6, Cs2NaY0.9Ho0.1Cl6 and Cs2NaGd0.99Ho0.01Cl6 has been investigated down to 10 K under 355 and 457.9 nm laser excitation, and at room temperature under 199.8 and 239 nm excitation. Well-resolved emission is observed from the 5G4 level near 25 700 cm−1 in the low-phonon elpasolite hosts and at 80 K hot bands are observed both to low and to high energy of the 5G4 → 5I6 transition. The failure to observe emission from other states above 21 000 cm−1 in Cs2NaHoCl6 at room temperature under the high energy excitation lines is attributed to the dominance of nonradiative cross-relaxation processes.