Fluorescence and phosphorescence of Cr 3+ in cubic hosts

Abstract

The low-temperature well-resolved 4T 2g → 4A 2g fluorescence spectrum of Cs 2NaYF 6:Cr 3+ is presented and interpreted. Strong vibrational progressions in the α 1g symmetric stretching and ε g stretching modes are based upon the zero phonon line and odd-parity vibronic origins. The Jahn–Teller stabilization energy in the 4T 2g state is 255 cm −1. The Cr 3+ emission has previously been assigned to Tm 3+ upconversion. The 4T 2g barycentre is strongly linearly correlated with metal–halogen distance for Cr 3+ diluted into elpasolite hosts. More generally, for Cr 3+ in other hosts, the metal–ligand distance divided by ligand formal charge exhibits a fairly linear relation with 4T 2g– 4A 2g energy separation, by contrast with the independence upon 2E g– 4A 2g energy separation.