Synthesis and characterization of Nb2O5:La3+,Eu3+ phosphors obtained by the non-hydrolytic sol-gel process

Abstract

The phosphor-converted light-emitting diode technique is an important solid-state illumination strategy. Sulfide-based materials are the most often employed red phosphors, but they are chemically unstable and present lower efficiency in comparison to the blue and green phosphors. Therefore, it is important to find a new red phosphor source that can emit intense red light while absorbing light in the near ultraviolet (UV) spectral region. This paper describes the photoluminescence properties of Nb2O5:La3+,Eu3+ obtained by the non-hydrolytic sol-gel process. The X-ray results indicated that the thermal treatment allowed to obtain the different crystalline structures such as, the orthorhombic and monoclinic phases for the Nb2O5 and the orthorhombic phase for the La2Nb10O28. This polymorphism was also confirmed by the Raman spectroscopy. The luminescence spectra revealed the existence of the Eu3+ ions in both crystalline phases for the samples annealed at higher temperature, depending of the excitation wavelength. The emission spectrum showed that increasing the annealing temperature promotes the narrowing of all intraconfigurational f-f transitions for the Eu3+ ions, due to the structural changes. In addition, all samples present good CIE (International Illumination Committee) chromaticity coordinates when excited in the UV (275 and 394 nm), blue (465 nm) and green (525 nm) radiation.