Markus Wermuth and Hans U. Güdel
Photon avalanche in Cs₂ZrCl₆: Os⁴⁺
J. Chem. Phys. 114, 1393-1404 (2001)                 

Abstract: 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 17000 cm^–1 is induced by NIR excitation between 10500 and 14500 cm^–1. The three excited states G₄(³T_1g), G₅ (¹T_2g), and G₁ (¹A_1g) with 15 K lifetimes of 20 ms, 8 ms, and 4 ms, respectively, in Cs₂ZrCl₆: 1% Os⁴⁺ participate in the upconversion. Excitation at the G₄ (³T_1g) G₁(¹A_1g) 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⁺.