XPS characterization and luminescent properties of GdNbO4 and GdTaO4 thin films

Surface chemical composition of gadolinium niobate GdNbO4 (GNO) and tantalate GdTaO4 (GTO) thin films was examined by X-ray photoelectron spectroscopy (XPS). XPS spectra confirmed Gd3+ and Nb5+ or Ta5+ valence states in films. The Gd 3d doublet was shown with energy difference equal Delta = 32.7 eV. Gd concentration (at %) reduced from 6 and 7% in GNO and GTO powder precursors to 3 and 2% in films, respectively. Experimental value of Gd/Nb/O and Gd/Ta/O ratio was determined 0.5:1:8.3 and 0.3:1:6.3. Luminescent properties of GNO and GTO films were measured for the first time. Excitation spectra of the GNO and GTO presented broad peaks at 257 and 263 nm, that were designated to the charge transfer bands (CTB) resulting to the O2- -> Nb5+ or O2- -> Ta5+ transition. Emission spectra reflected strait peak at 312 nm ascribed to the Gd3+ 4f-4f intraconfigurational transition S-8(7/2) -> P-6(7/2) and wide peak at about 360 nm related to the CTB transition of NbO43- and TaO43- groups. Time-resolved spectrum was described by two components at 315 and 311 nm assigned P-6(7/2) -> (8)S(7/2 )and P-6(7/2) -> (8)S7/2 transition, respectively in both films destined such as sensors and display devices.