Photon avalanche in Cs2ZrCl6: Os4+

The visible (VIS) upconversion luminescence of Cs2ZrCl6: x% Os4+ (x=0.1,1) upon excitation in the near infrared (NIR) is presented and analyzed. The crystals of Cs2ZrCl6: x% Os4+ (x=0.1,1) were synthesized by the Bridgman technique. VIS luminescence around 17 000 cm−1 is induced by NIR excitation between 10 500 and 14 500 cm−1. The three excited states Γ4 (3T1g), Γ5 (1T2g), and Γ1 (1A1g) with 15 K lifetimes of 20 ms, 8 μs, and 4 μs, respectively, in Cs2ZrCl6: 1% Os4+ participate in the upconversion. Excitation at the Γ4 (3T1g)→Γ1 (1A1g) energy shows the typical fingerprints of a photon avalanche. The dynamics of this excitation are calculated with a rate-equation model, and the observed concentration and temperature dependence of the processes are analyzed. The upconversion behavior of Cs2ZrCl6: x% Os4+ (x=0.1,1) is compared with the bromide analog Cs2ZrBr6: 0.2% Os4+.