Tunable Luminescence of Ce3+-Doped Calcium Boroaluminate Glasses for Light Emitting Devices

Abstract

In this work, the visible luminescence of Ce3+-doped calcium boroaluminate glasses (CaBAl) was 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 melt-quenching technique, adding carbon as a reducing agent. The samples studied had amorphous nature confirmed by the results of X-ray diffraction (XRD). The Fourier transform infrared (FTIR) results showed that the vitreous network is formed by BO3 and BO4 structures, and the calculated values of the fraction of BO4 groups (N4) revealed that the increment of cerium favored the conversion of BO3 to BO4. The optical absorption spectra presented an intense broad band assigned to a charge transfer of the Ce4+, with a shift of ultraviolet (UV) absorption edge to longer wavelength, and a decrease in the band gap as result of the CeO2 concentration increase. The photoluminescence excitation (PLE) spectra showed that Ce3+-doped CaBAl glasses can be excited in a wide range of the UV spectral region (320-405 nm). The luminescence band of Ce3+ transitions 5d1 → 2F5/2, 2F7/2 was observed with different maximum in the emission bands for different excitation wavelengths, originate from Ce3+ ions placed mainly in two different sites in the glass network, resulting in distinct band positions and symmetries. The International Commission on Illumination (CIE) diagram demonstrated that the emission of samples occurs in the blue region. The lifetime decreased with increasing CeO2 concentration (47 to 34 ns) from 1.25 to 0.25 mol.% of CeO2. The results suggest that the studied glasses have potential for applications in optical devices such as LEDs and phosphors.