Luminescence properties of neodymium, samarium, and europium niobate and tantalate thin films.

Thin films of lanthanide orthoniobate LnNbO 4 (LnNO) and orthotantalate LnTaO 4 (LnTO), (Ln = Nd, Sm, Eu) were fabricated using the sol-gel method with subsequent spin-coating on the PbZrO 3 /Al 2 O 3 substrate and annealing at 1000°C. X-ray diffraction patterns showed monoclinic M-LnNbO 4 or M´-LnTaO 4 , which coexists with the orthorhombic or tetragonal phase. X-ray photoelectron spectroscopy demonstrated the presence of Nd 3+ , Sm 3+ /Sm 2+ and Eu 3+ /Eu 2+ ions. The luminescence properties of polymorphic films were investigated. Excitation spectra of PbZrO 3 interlayer represented broad bands at 410 and 550 nm that were assigned to charge transfer bands (CTB). In all films, the CTB broad band at ~275 nm related to charge transfer transition of Ln 3+ →O 2- and NbO 4 3- or TaO 4 3- groups. In excitation spectra, 4 I 9/2 → 4 G 5/2 (Nd 3+ ), 6 H 5/2 → 6 P 3/2 (Sm 3+ ) and 7 F 0 → 5 L 6 (Eu 3+ ) transitions (at 585, 402 and 395 nm), respectively were found to be more intense than any other Ln 3+ transition. The emission spectra showed narrow and intense bands at 1065, 600, and 614 nm that were ascribed to Nd 3+ , Sm 3+ , and Eu 3+ 4f-f intraconfigurational transitions 4 F 3/2 → 4 I 11/2 , 4 G 5/2 → 6 H 7/2 , and 5 D 0 → 7 F 2 , respectively. The excellent luminescence properties of films make them new potential groups for visible and/or near-infrared applications such as sensors and imaging equipment.