Electronic structure and optical spectra of Au− ions in RbCl

Abstract

Ab initio wavefunction based quantum chemical calculations on the electronic structure and optical spectra of Au− ions in RbCl crystals are reported in this work. ns2 impurities in alkali halides are prototypical phosphor materials and have been extensively studied. In particular, RbCl:Au− has been recently studied experimentally, but some points of the interpretation of the spectra are still controversial. Our calculations, that include all the major interactions present in the system, show very good agreement with the experimental findings. The calculations show that the levels belonging to the 5d96s26p electron configuration lie relatively low in energy, and extensive mixing with some of the 6s6p levels is found. Large mixing of singlet and triplet states via spin-orbit coupling is found for most of the calculated levels. Due to this, band C in the absorption spectrum is found to consist of two transitions, to the 2 T1u and 3 T1u electronic levels, described as configurational mixtures of 6s6p-1P1 and 5d96s26p levels. Transitions to 5d96s26p levels are found to be responsible for the D absorption bands of the material. On the other hand, emission band C′ is assigned to a transition from the 1 A2u (5d96s26p) electronic level to the ground level, a transition that is electric dipole forbidden. This level lies just below the levels responsible of the C absorption (around 200 cm−1). These findings can justify the complex behavior of this C′ emission.