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

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 → ²F_5/2, ²F_7/2 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.