Efficient white upconversion luminescence in Yb3+/Eu3+ doubly-doped transparent glass ceramic

Low-Temperature Fluoro-Borosilicate Glass for Controllable Nano-Crystallization in Glass Ceramic Fibers

A fluorosilicate (FS) nano-crystallized glass ceramic (NGC) is one of the most commonly used gain materials for applications in optical devices due to its excellent thermal stability as well as high-efficiency luminescence. However, FS glass can hardly be used to prepare NGC fibers due to its high preparation temperature. Here, a series of low-temperature fluoro-borosilicate (FBS) glasses were designed for the fabrication of active NGC fibers. By modulating B2O3, the preparation temperature of FBS glass was reduced to 1050 °C, and the crystallization in FBS NGCs was more controllable than in FS NGC. The crystallization of the impure phase was inhibited, and single-phase rare earth (RE)-fluoride nanocrystals were controllably precipitated in the FBS NGCs. The 40Si-20B FBS NGC not only exhibited a higher optical transmittance, but the luminescence efficiency was also much higher than traditional FS NGCs. More importantly, NGC fibers were successfully fabricated by using the designed FBS glass as core glass. Nanocrystals were controllably precipitated and greatly enhanced, and upconversion luminescence was observed in NGC fibers. The designed FBS NGCs provided high-quality optical gain materials and offered opportunities for fabricating a wide range of NGC fibers for multiple future applications, including fiber lasers and sensors.

Optical band gaps and spectroscopy properties of Bi m+/Eu n+/Yb3+ co-doped (m = 0, 2, 3; and n = 2, 3) zinc calcium silicate glasses

In this study, the indirect/direct optical band gaps and spectroscopy properties of Bi ^m+/Eu ⁿ⁺/Yb³⁺ co-doped (m = 0, 2, 3; and n = 2, 3) zinc calcium silicate glasses under different excitation wavelengths were investigated. Zinc calcium silicate glasses with the main compositions of SiO₂-ZnO-CaF₂-LaF₃-TiO₂ were prepared by the conventional melting method. EDS analysis was performed to determine the elemental composition existing in the zinc calcium silicate glasses. Visible (VIS)-, upconversion (UC)-, and near-infrared (NIR)-emission spectra of Bi ^m+/Eu ⁿ⁺/Yb³⁺ co-doped glasses were also investigated. Indirect optical band gaps and direct optical band gaps of Bi ^m+-, Eu ⁿ⁺- single-doped, and Bi ^m+-Eu ⁿ⁺ co-doped SiO₂-ZnO-CaF₂-LaF₃-TiO₂-Bi₂O₃-EuF₃-YbF₃ zinc calcium silicate glasses were calculated and analyzed. CIE 1931(x, y) color coordinates for VIS and UC emission spectra of Bi ^m+/Eu ⁿ⁺/Yb³⁺ co-doped glasses were determined. Besides, the mechanism of VIS-, UC-, NIR-emissions, and energy transfer (ET) processes between Bi ^m+ and Eu ⁿ⁺ ions were also proposed and discussed.

Crystal phase modified blue upconversion on Tm3+/Yb3+:BCZT ceramic phosphor benefits multifunctionality in white-light applications

Rare earth (RE) doped perovskite oxide hosts especially titanates, are promising phosphor materials in terms of white-light emission owing to their extraordinary properties such as an exceptional hosting environment for RE-ions and a switchable crystal phase near the phase boundary. Here, we report a new strategy of crystal phase modification to enhance the blue upconversion (UC) efficiency to such an extent that the combinational mixing of blue and green/red-emitting phosphor gives intense white emission. The Lead free (Ba_0.85Ca_0.15)(Zr,Ti)O₃ ceramics were synthesised at different sintering temperatures by incorporation of Tm³⁺/Yb³⁺ ions as dopants. The UC quantum efficiency of the Tm³⁺/Yb³⁺:BCZT sample sintered at 1300 °C was recorded at different excitation power densities. It was observed that the crystal phase transformation from tetragonal to rhombohedral symmetry in the sample near the phase boundary plays a cruicial role in improving the quantum efficiency. White-light emission applications were demonstrated by preparing biphasic samples with powder mixing of a BCZT:Tm³⁺/Yb³⁺ (blue-emitting) + BCZT:Er³⁺/Yb³⁺ (green/red-emitting) phosphor, and their composition were optimised at a mixed ratio. Thereafter, photometric characterization (CIE chromaticity, colour purity and corelated colour temperatures) was performed, and it indicated the suitability of the current biphasic samples in direct white-light (cooler) applications on an industrial scale. Crystal phase modified blue emission efficiency enhancement is a key feature of this work, which helps to generate approximately pure white-light with ideal chromacity (∼0.333, 0.343) emission when Tm³⁺/Yb³⁺:BCZT is mixed with a green emitting BCZT:Er³⁺/Yb³⁺ phosphor.