Estudo das propriedades estruturais, ópticas e luminescentes de vidros Cálcio Boro-aluminato dopados com Ce3+ para dispositivos emissores de luz sintonizável

Abstract

Rare-earth doped glasses have been extensively studied due to several promising applications in optical and optoelectronic devices. In this work the visible luminescence of Ce3+ -doped calcium boroaluminate (CaBAl) glasses has been studied. Samples of CaBAl glass with composition (30.97-x)CaO-49.90B2O3-10.22Al2O3-8.90CaF2-xCeO2, with values of x varying from 0.25 to 1.25 mol%, were prepared by the conventional melting-quenching technique, adding carbon (as graphite) as reducing agent. The results of XRD confirmed the amorphous nature of the studied glasses. The increase in the volumetric density and the decrease of the molar volume indicated that the addition of cerium causes a modification in the glass structural units. The FTIR results showed that the vitreous network is formed by BO3 and BO4 structures and the calculated N4 values revealed that increment of cerium favored the conversion of structural units from BO3 to BO4. From DTA analysis was observed an increase of Tg values and a decrease of Tx with increase of dopant. The absorption spectra presented an intense broad band assigned to a charge transfer of the Ce4+, with a shift of UV absorption edge towards longer wavelength and, consequently, the decrease in the band gap with the increase in CeO2 concentration. Excitation spectra showed that Ce3+ -doped CaBAl glasses can be excited in a wide range of the UV spectral region. The luminescence band of 5D1→2F5/2,7/2 transitions of Ce3+ ions, with excitation at 320 and 405 nm, was observed. For excitation at 320 nm the emission presented greater intensity for samples with 0.25 mol% of CeO2 and for excitation at 405 nm the sample of 1.00 mol% presented greater intensity. The observed differences in emissions, for different excitation wavelengths, originates from Ce3+ ions placed mainly in two different sites of the glass network, resulting in distinct band positions and symmetries. The CIE diagram demonstrated that the samples emissions occur in the blue region. The excited state lifetime values, obtained from luminescence decay curves, show a decrease with increasing CeO2 concentration (47 to 34 ns) for the concentrations of 1.25 to 0.25 mol% of CeO2. The results suggest that the studied glasses have potential applications in optical devices such as LED and phosphors.