Optical spectroscopy of Pr3+ in KGd(WO4)2 single crystals

Abstract

The polarized optical absorption (OA) and photoluminescence of Pr3+ doped KGd(WO4)(2) (KGW) single crystals have been measured at selected temperatures between 7 and 300 K. For the studied Pr concentrations, [Pr] = 0.03 x 10(20)-1.9 x 10(20) cm(-3) a unique site is observed. 74 energy levels were experimentally determined for this site and labelled with the appropriate A or B irreducible representations corresponding to the C-2 symmetry of the Gd point site in KGW. The set was fitted to a Hamiltonian of adjustable parameters including free-ion as well as real B-q(k) and complex S-q(k) crystal-field parameters. A good simulation of the experimental crystal field energies was achieved with a root mean square deviation sigma = 15.3 cm(-1). Distortions in the oxygen bonds to Pr3+ are found to contribute to the broadening of some OA bands, particularly those related to the D-1(2) multiplet. The OA edge is determined by the interconfigurational 4f--> 4f(1)5d(1) Pr3+ transition peaking at 34 200 cm(-1). From the average 300 K OA cross sections the radiative lifetimes of the Pr3+ multiplets have been calculated considering the standard and modified Judd-Ofelt (JO) theories. A better agreement with the experimental results is obtained by the standard theory: the average JO parameters obtained at (Omega)over-bar(2) = 12.0 x 10(-20) cm(2), (Omega)over-bar(4) = 8.15 x 10(-20) cm(2) and (Omega)over-bar(6) = 2.64 x 10(-20) cm(2). Electrons excited to the P-3(0) multiplet decay very efficiently to the D-1(2) multiplet even at 15 K. In samples with [Pr] greater than or equal to 0.3 x 10(20) cm(-3) the excitation of the D-1(2) multiplet decays non-radiatively by an electric dipole-dipole transfer between Pr neighbours.This work is supported by CICyT under projects TIC96-1039 and MAT99-1077 and by MONOCROM SL (Spain).Peer reviewe