Enhanced NIR down-conversion of Yb3+ in fluorosilicate glass-ceramics co-doped with Bi ions

The fluorescence properties of Bi3+/Yb3+ co-doped SiO2-Al2O3-P2O5-YF3 glasses and glass-ceramics are investigated. The 6s2-type Bi3+ is used as a novel sensitizer for near infrared (NIR) down-conversion (DC) of Yb3+ ions due to its allowed excitations favorable to the high absorption of excited energy. Involvement of the energy transfer (ET) process from Bi3+ to Yb3+ under the ultraviolet (UV) excitation is demonstrated for all Bi3+/Yb3+ co-doped glass samples. Based on crystallization kinetics analysis, thermal treatment is performed on glass samples under different heating conditions to induce homogeneous nucleation and crystal growth. Emission and excitation spectra as well as Bi3+ emission decay curves confirm that the ET from Bi3+ to Yb3+ is tremendously intensified due to proper crystallization treatment. The possible ET mechanism is discussed with the help of the simplified energy level diagrams of Bi3+ and Yb3+. The present Bi3+/Yb3+ co-doped glass ceramics are likely applied to solar cells via spectrum conversion.