Thermal reduction-triggered full-color tuning of Eu3+/Eu2+/Tb3+ co-doped sintered nanoporous Al2O3-SiO2 glass for WLEDs

The development of advanced luminescent materials is highly desirable for developing the energy-efficient lighting technology. However, it is still challenging to achieve stable full-color tuning in the same matrix upon a single-beam light excitation so as to ensure the high color stability and consistency. Herein, Eu ³⁺/Eu ²⁺/Tb ³⁺ co-doped sintered nanoporous glass via the dipping strategy is fabricated, which can emit blue, green and red emissions simultaneously by simply modifying the thermal treatment temperature. This full-color tuning is attributed to the dual roles of the thermal reduction of Eu ³⁺ to Eu ²⁺ in Al ₂O ₃-SiO ₂ glass and simultaneous emissions of Eu ³⁺/Eu ²⁺/Tb ³⁺ activators. The densification of nanoporous glass via sintering could effectively decrease the amount of hydroxyl groups that present in the glass matrix, resulting in 5 times enhancement of the photoluminescence intensity and longer photoluminescence lifetime of rare earth (RE) ions. The thermal reduction of Eu ³⁺ to Eu ²⁺ is due to the reduction environment provided by Al ³⁺ ions in the Al ₂O ₃-SiO ₂ glass. The energy transfer (ET) from Eu ²⁺ to Tb ³⁺, Eu ²⁺ to Eu ³⁺ and Tb ³⁺ to Eu ³⁺ have been investigated in detail. Based on the ET mechanism, rational PL spectra design was demonstrated by varying the concentration of Eu ³⁺ ions in solution. The Color Correlated Temperature (CCT) and the Color Rendered Index (CRI) values of the white light emission glass are 7420 K (Cold-white emission) and 80.85, the temperature dependent photoluminescence (TDPL) analysis reflects the white light emission glass possesses high thermal stability and excellent thermal restorability. This facile fabrication and full-color tuning of Eu ³⁺/Eu ²⁺/Tb ³⁺ co-doped sintered nanoporous Al ₂O ₃-SiO ₂ glass may provide a novel luminescent material for white-light emitting diodes (WLEDs) application.