High pressure effects on the structure and spectroscopy of V3+ substitutional defects in Cs2NaYCl6.: An ab initio embedded cluster study

In this paper we present the results of ab initio model potential embedded cluster average coupled pair functional calculations on (VCl6)(3-) embedded in a reliable representation of the Cs2NaYCl6 host. They are aimed at complementing recent high pressure, room temperature, broad band luminescence studies with detailed theoretical data. In particular, we study the effects of high hidrostatic pressure (i) on the structure of V3+ substitutional defects in four low lying electronic states (a(3)T(1g), T-3(2g), T-1(2g), and b(3)T(1g)), (ii) on the individual a(1g) and e(g) force constants and equilibrium displacements, and (iii) on the zero-phonon and Franck-Condon energy differences between them. It is shown that only the e(g) equilibrum displacements between different electronic sates are large and pressure dependent, while the a(1g) ones are small and essentially pressure independent. A value of kappa=4x10(-3) kbar(-1) is suggested for the isothermal bulk modulus of the Cs2NaYCl6 elpasolite, because it allows for an excellent match between the theoretical dependence on the unit cell volume and the experimental dependence on applied pressure of several properties: equilibrium displacements, vibrational frequencies, and minimum-to-minimun and vertical energy differences. (C) 2003 American Institute of Physics.