Terbium and europium co-doped NaAlSiO4 nano glass-ceramics for LED application

Terbium and europium doped homogeneous glasses from the system Na2O-Al2O3-SiO2-NaBO2 are prepared with two different dopants concentrations - Tb3+:Eu3+ = 0.25:0.05 and Tb3+:Eu3+ = 0.33:0.033 at.%. Glass-ceramics are obtained after thermal treatment of the parent glass at 650 °C during 5 and 24 h. The crystallizing phases, the degree of crystallinity and the particle size are determined. The main crystallizing phase after thermal treatment is NaAlSiO4. X-ray analyses show the presence of Na2SiO3 as the second phase. The crystallinity degree after 24 h thermal treatment at 650 °C of the glass-ceramic samples is up to 98%. The particle size for NaAlSiO4 is between 50 and 70 nm and for Na2SiO3 - between 30 and 70 nm. Emission and excitation spectra of the glass-ceramics show the characteristic peaks of Tb3+ and Eu3+ with an overlap of the terbium ion and europium ion spectra in the range 570-640 nm. Analyses of the excitation and emission spectra of glass-ceramic samples show the ability for energy transfer between Tb3+ and Eu3+ ions. The spectra show different intensity of the dopants characteristic emissions, i.e. variations in colors. This result suggests that the emission color can be controlled by the dopant ions concentrations and the thermal treatment conditions. Glass-ceramic sample with dopants ratio Tb3+:Eu3+ = 0.33:0.033 thermal treated 24 h possess CIE coordinates very close to white light (0.332, 0.305).