NIOBIUM OXIDE BASED PHOSPHORS: EFFECT OF ANNEALING PROCESS ON THE LUMINESCENCE PROPERTIES

Abstract

Purpose: Luminescent materials such as phosphors are materials that emit light in the visible, ultraviolet and infrared regions under external energy excitation. Among the materials which present promising applications in this field, the matrices based on niobium oxides have attracted attention due to its properties, such as, the band-gap (3.6 eV), the low cut-off phonon energy (900 cm -1 ) and the relative high refractive index (~2.2). Methods: In this work, niobium oxide based matrices doped with Ln 3+ (Ln 3+ = La, Eu and Tm) was prepared by the Non-Hydrolytic Sol-Gel route and the effect of the temperature of heat treatment (550 or 900C – 4h) on the structural and luminescent properties was investigated by X-ray powder diffraction (XRD) and photoluminescence (PL). Results: XRD results showed mixtures of crystalline phases of niobium oxide and oxychlorides of niobium and lanthanum for the samples treated at 550oC while that sample treated at 900oC presented the niobium oxide and lanthanum niobate phases. The excitation and emission spectra presented peaks attributed to the europium and thulium intra-configurational transitions. For the sample treated at 900°C, it was also observed a broad band at around 270 nm in the excitation spectra which is related to the charge transfer band (CTB) from O 2- 2p orbital to Nb 5+ empty 4d orbital. Conclusion: The results suggested that the annealing temperature presented an important role on the structural and luminescence properties, once higher temperature provided higher crystallinity and consequently thinner emission bands.