White-light luminescence from Tm3+-doped borosilicate glass-ceramics synthesized by the sol-gel route

Abstract

White-light luminescent Tm3+-doped borosilicate glass-ceramics were synthesized by the sol-gel method. The materials are predominantly amorphous with some embedded nanocrystals of H3BO3 and B2O3 with sizes ranging from 4 to 10 nm, which decrease as the Tm2O3 content is increased. Moreover, the glass transition and crystallization temperatures enhance with the Tm2O3, showing higher thermal stability in the glass-ceramic with 0.50 mol%. Also, the addition of Tm2O3 promotes an increase in the non-bridging oxygen concentration, the occurrence of the boric anomaly, and the incorporation of a higher amount of C species (CC and CO bonds) into the reticular structure of the glass ceramic. Therefore, the optical bandgap reduces (3.62–3.47 eV) while the photoluminescence intensity increases, being maximum at 0.75 mol% of Tm2O3. Interestingly, the luminescent glass-ceramics show a white-emission color, CIE coordinates are (0.31–0.33, 0.33–0.34) instead of those corresponding to blue, which is what usually occurs in other Tm3+-doped materials. This characteristic photoluminescence emission is due to the 1D2→3F4 electronic transitions of Tm3+ ions and the π– π* and n–π* transitions of CC and CO bonds originated by the carbon remnants inside the glass-ceramics. The released white emission has a correlated color temperature of 5600–6650 K, a color rendering index of ∼88, and a quantum yield of 12.3%. These materials are promising candidates for their use as phosphors in solid-state white-light-emitting devices.