Thermal reduction triggered red–orange to blue-violet color-tunable Eu doped bulk transparent nanoporous Al2O3-SiO2 glass for LEDs

Nanoporous Al 2 O 3 -SiO 2 glasses were prepared using a sol–gel method. These sintered nanoporous Al 2 O 3 -SiO 2 glasses have a transmittance greater than 85 % and possess high mechanical strength, enabling them to contain and protect RE ions. Owing to the presence of nanopores in nanoporous Al 2 O 3 -SiO 2 glasses, Eu ions can easily enter the nanoporous Al 2 O 3 -SiO 2 glasses via an ex-situ dipping method. After drying at room temperature (RT) and then heating at 400 °C, 600 °C, 800 °C, and 1200 °C, we obtained a series of Eu doped nanoporous Al 2 O 3 -SiO 2 glasses. The thermal reduction process from Eu 3+ ions to Eu 2+ ions can occur at a lower sintering temperature (400 °C), enabling a detailed analysis of the thermal reduction mechanism at both low and high temperatures in detail. Under the conditions where Al 3+ ions are present in the samples that are under calcination, Eu 2+ -doped nanoporous Al 2 O 3 -SiO 2 glasses are more easily obtained at relatively low temperatures. Owing to the adjustable composition of Eu 3+ /Eu 2+ in the nanoporous Al 2 O 3 -SiO 2 glasses, tunable emission from red-orange light to blue-violet light can be achieved in the samples. This new type of transparent Eu-doped NPGs has the advantages of high mechanical strength and good processability and is non-toxic and harmless, thereby showing great potential for use in tunable light sources and LED devices.