The nature of the luminescence of niobates MNbo3 (M = Li, Na, K)

On the Luminescence of Ba5M4O15(M=Ta5+, Nb5+)

“…Since this causes a reduction in ¼, the first absorption transition occurs at high energy ( &230 nm). The similarity in the optical properties of LiTaO and Ba NaTaO , with structurally isolated [TaO ]\ groups is thus not surprising (see Table 1) (5,8).…”

“…This is discussed below. Delocalization of the excited state is expected to occur in a structure which offers three-dimensional coupling of the d metal ion polyhedra through corner sharing when the ML>-ligand-ML> bond angle approaches 180° (5). In such cases, the bandwidth (¼) of the nd excited state is expected to be quite broad.…”

“…We first discuss the relative energy position of the first excitation band maxima in Ba Ta O , Sr Ta O , KTaO , and LiTaO ( Table 1). The luminescence of LiTaO has been interpreted in terms of isolated tantalate groups in the perovskite lattice (5). The electronic isolation of the tantalate group occurs due to the considerable deviation of the Ta>-O-Ta> bond angles ( &125°) from a linear configuration.…”

Low temperature X-ray luminescence of KNbO3 crystals

“…No luminescence bands have been excited at temperatures above 45 K, in agreement with [10,12], but in contradiction with [13,15,16]. A probable explanation of the above fact is that the Fe ion concentration in our sample is considerably lower than that in the samples studied in [13,15,16].…”

“…Two photoluminescence bands at 420 and 530 nm have been reported in powders of KNbO 3 [10], where these two bands have been ascribed to self-trapped exciton emission from the NbO 6 octahedron of two di erent crystal modi®cations of KNbO 3 [10,14]. It was indicated that the quenching temperature (at which the luminescence intensity has decreased by 50% of the intensity at liquid helium temperature) for 420 and 530 nm emission bands were 70 and 35 K, respectively.…”