The [formula omitted] luminescence spectrum of [formula omitted] in [formula omitted]2GeF 6 crystals—A quantum chemical study

Abstract

The 5 f 1 6 d ( t 2 g ) 1 emission spectrum of Cs 2GeF 6:U 4+ single crystals has been calculated using the relativistic ab initio model potential (AIMP) embedded cluster method. It consists of a series of broad, intense bands in the UV followed by broad and increasingly weaker bands in the visible and near infrared spectral range, which appear to be associated with emissions from the lowest 5 f 1 6 d ( t 2 g ) 1 excited state, 1 E u , to a number of levels of the 5 f 2 manifold. The electric dipole allowed emission of highest energy, 1 E u → 1 T 1 g , is found to have very low oscillator strength, - 0.115 × 10 - 2 ; this value is only 4% of the most intense electronic transition: 1 E u → 1 T 2 g whose electronic origin is found to be at 34 200 cm - 1 . A very large Stokes shift of 6200 cm - 1 is obtained, which should result in low luminescence quenching due to reabsorption and should favourably contribute to the emission quantum efficiency. The lifetime of the spontaneous emission from 1 E u has been calculated to be in the nanoseconds range: 33 ns.