Photoluminescence Spectroscopy of Chromium Doped Cd 2 Nb 2 O 7.

Photoluminescence (PL) spectra and thermoluminescence (TSL) of Cr doped Cd 2 Nb 2 O 7 were investigated for the first time. The 12 - 300 K and 350 - 900 nm temperature-spectral regions were inspected. It was found that PL spectrum consists of four narrow emission lines centered at 737.7, 737.1, 736.7, and 736.5 nm accompanied by vibrational sidebands with excitation bands at 650, 500, and 370 nm ( T = 12 K). Emission lines are attributed to the zero-phonon transitions 2 E → 4 A 2 of two kinds of octahedral coordinated Cr 3+ centers, which substitute Nb, with local charge compensating oxygen vacancy and with non-local compensation. TSL revealed temperature maxima of intensity at 98 and 183 K. Activation energies of PL quenching at T < T c = 196 K and for T > 196 K appeared to be 122 meV and 216 meV, respectively. This effect is tentatively explained by the change of the adiabatic potential of the Cr 3+ centers upon a ferroelectric phase transition of CNO at T c . [ABSTRACT FROM AUTHOR]