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 D5h, as present in other rare earth pyrogermanates, and not C1. 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 vertical bar SLJMJ> states spanning the entire 4f2 ground configuration of Pr3+ in the intermediate coupling formalism, including J-mixing under CF. The best fitted free ion and CF parameters obtained were E1=4335.0, E2=23.1, E3=464.0, ζ=775.0 α=22.9, β=-674.0, γ=1520.0, B20=-100, B40=1650, B60=-1600 and B65=-1000 (all in cm-1). Using these parameters the thermal characteristics of molar magnetic susceptibilities (Kparallel, Kperpendicular), their anisotropy ΔK=±(Kparallel-Kperpendicular) and the Schottky specific heat (CSch) of Pr3+ in YPG were calculated. It was found that the calculated values of Kparallel >Kperpendicular between 300 and 152 K (Ti) but on cooling further Kperpendicular >Kparallel was observed, i.e. the sign of ΔK was reversed below Ti. The calculated values of CSch exhibited a sharp peak at 24 K and a broad maximum at 156 K. These characteristics were similar to other Pr3+ compounds studied earlier. (author)