Oliver S. Wenger and Hans U. Güdel
Luminescence spectroscopy of V³⁺-doped Cs₂NaYCl₆ under high pressure
Chem. Phys. Lett. 354, 75-81 (2002)                 

Abstract: The luminescence behavior of 1% V³⁺:Cs₂NaYCl₆ at room temperature is studied as a function of hydrostatic pressure. At ambient pressure the V^{3+ 3}T_2g excited state origin lies 234 cm^–1 above the ¹T_2g first excited state. At room temperature the two states are in thermal equilibrium, and spin-allowed ³T_2g ³T_1g emission is dominant. Pressure increases the energetic separation of ¹T_2g and ³T_2g, leading to a decreasing ³T_2g steady state population at constant temperature. This manifests itself in an increasing relative amount of spin-forbidden ¹T_2g ³T_2g luminescence, as evidenced by the occurrence of sharp luminescence features and an increase in the luminescence decay time at higher pressures.