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

Thin films of lanthanide orthoniobate LnNbO4 (LnNO) and orthotantalate LnTaO4 (LnTO), (Ln = Nd, Sm, Eu) were fabricated by sol-gel method with subsequent spin-coating on PbZrO3 /Al2 O3 substrate and annealing at 1000°C. X-ray diffraction patterns showed monoclinic M-LnNbO4 or M´-LnTaO4 , which coexists with orthorhombic or tetragonal phase. X-ray photoelectron spectroscopy demonstrate presence of Nd3+ , Sm3+ /Sm2+ and Eu3+ /Eu2+ ions. Luminescence properties of polymorphic films were investigated. Excitation spectra of PbZrO3 interlayer represented broad bands at 410 and 550 nm, that were assigned to charge transfer bands (CTB). In all films, CTB broad band at around 275 nm related to charge transfer transition of Ln3+ → O2- and NbO4 3- or TaO4 3- groups. In excitation spectra, 4 I9/2 → 4 G5/2 (Nd3+ ), 6 H5/2 → 6 P3/2 (Sm3+ ) and 7 F0 → 5 L6 (Eu3+ ) transitions (at 585, 402 and 395 nm), respectively are found to be more intense than any other Ln3+ transition. The emission spectra showed narrow and intense bands at 1065, 600 and 614 nm ascribed to Nd3+ , Sm3+ and Eu3+ 4f-f intraconfigurational transition 4 F3/2 → 4 I11/2 , 4 G5/2 → 6 H7/2 and 5 D0 → 7 F2 , respectively. The excellent luminescencent properties of films make them new potential group for visible and/or near-infrared applications such as sensors and imaging equipments.