Impacto do nióbio em materiais luminescentes: vidros fosfato nanoestruturados com CdS e dopados com terras raras

Abstract

Niobium pentoxide (Nb2O5), when incorporated into glasses doped with trivalent rare–earth ions (RE3+), has attracted growing interest from the scientific community due to its potential for the development of luminescent materials for optical device applications. In this study, two sets of samples based on the PANK phosphate glass matrix were investigated: PANK – zNb2O5 and PANK – yCdS – zNb2O5, both doped with neodymium oxide (Nd2O3) and europium oxide (Eu2O3). The objective was to investigate the impact of Nb2O5 addition on the structural and luminescent properties of these glass systems. The samples were characterized by Raman spectroscopy, optical absorption, photoluminescence (PL), time–resolved photoluminescence, including temperature–dependent measurements, and differential thermal analysis (DTA). The results indicate that Nb2O5 acts predominantly as a network former, promoting a reduction in the phonon energy of the glass systems. This structural modification was corroborated by the increase in the relative intensity ratio (R) and in the Judd–Ofelt intensity parameter (Ω_2), which indicated greater asymmetry of the sites occupied by the RE3+ ions. In the Eu2O3–doped samples, the PL spectra showed that the incorporation of Nb2O5 increases the intensity of the emission band centered at 612 nm, associated with the hypersensitive transition (5D0 → 7F2). The analysis of the PL decay curves revealed that, in the nanostructured system containing CdS nanocrystals (NCs), the RE3+ ions are distributed between two distinct low–symmetry average sites. In the glass system without CdS, on the other hand, these ions occupy a single low–symmetry average site. In both investigated sets, the lifetimes of the metastable 4F3/2 level of Nd3+ and the 5D0 level of Eu3+ decreased with increasing Nb2O5 concentration, indicating that the structural changes are modulating the radiative and non–radiative emission rates of the RE3+ ions. All analyzed samples exhibited branching ratios equal to or greater than 70% for the hypersensitive Eu3+ transition. In the glass system without CdS, the PL quantum efficiency of Eu3+ increased from 79% in the Nb2O5–free sample to 93% in the sample with the highest Nb2O5 concentration. These results demonstrate that Nb2O5 acts as an efficient modulator and enhancer of the structural and luminescent properties of phosphate glasses, making niobium–phosphate glasses promising for the development of advanced photoluminescent materials with potential applications in photonic devices.