Optical absorption spectra of Pr3+ doped in yttrium pyrogermanate (Y2Ge2O7) crystal

This paper reports the low temperature absorption and Zeeman spectra of Pr3+ doped in yttrium pyrogermanate (YPG), which were studied for the first time. In this compound the site symmetry of Pr3+, or the crystal field (CF) symmetry, was found to be D-5h, as present in other rare earth pyrogermanates, and not C-1. The spectral results were analysed by diagonalizing the total Hamiltonian consisting of the atomic (electrostatic, spin-orbit and configuration interactions) and the CF interactions, in a basis of 91\SLJM(J)] states spanning the entire 4f(2) ground configuration of Pr3+ in the intermediate coupling formalism, including J-mixing under CE The best fitted free ion and CF parameters obtained were E-1 = 4335.0, E-2 = 23.1, E-3 = 464.0, zeta = 775.0, alpha = 22.9, beta = -674.0, gamma = 1520.0, B-20 = -100, B-40 = 1650, B-60 = -1600 and B-65 = -1000 (all in cm(-1)). Using these parameters the thermal characteristics of molar magnetic susceptibilities (K-parallel to, K-perpendicular to), their anisotropy Delta K = +/-(K-parallel to - K-perpendicular to) and the Schottky specific heat (C-Sch) of Pr3+ in YPG were calculated. It was found that the calculated values of K-parallel to > K perpendicular to. between 300 and 152 K (T-i) but on cooling further K-perpendicular to > K-parallel to was observed, i.e, the sign of Delta K was reversed below T-i. The calculated values of C-Sch exhibited a sharp peak at 24 K and a broad maximum at 156 K. These characteristics were similar to other Pr3+ compounds studied earlier.