STEADY-STATE AND TIME-RESOLVED LASER SPECTROSCOPY OF CR3+ AND ND3+ SINGLY AND DOUBLY DOPED CALCIUM NIOBIUM GALLIUM GARNET

The optical properties of C3+, Nd3+, and Cr3:Nd3+ ions in Ca3(GaNb)2Ga3O12 (CNGG) garnet have been investigated in the 4.2-550 K temperature range by using steady-state and time-resolved laser spectroscopy. The luminescence of trivalent chromium in a singly doped crystal shows a strong thermal quenching above room temperature, which can be analyzed on the basis of the quantum-mechanical single-configurational-coordinate model by using the Struck-Fonger method. Low-temperature absorption, excitation, and time-resolved luminescence spectra of the Nd3+ ion in a singly doped crystal show inhomogeneous broadening associated with the existence of different sites for Nd3+ ions. Cr3+-to-Nd3+ radiative and nonradiative energy transfer has been demonstrated from the time-resolved emission spectra and the decrease of the Cr3+ fluorescence lifetime. The nonradiative Cr3+-->Nd3+ energy transfer is consistent with a dipole-dipole transfer process.