Luminescence from Nd³⁺ -doped GeO₂/ormosil organic-inorganic hybrid transparent dried gels

Nd³⁺ -doped GeO₂/ormosil transparent dried gel with the molar composition of 30GeO₂-70ormosil-0.5Nd₂2O ₃ was prepared by a sol-gel process from an organic-inorganic hybrid system at a low temperature of 100°C. Acid-catalyzed solutions of γ-glycidoxypropyltrimethoxysilane mixed with gemanium isopropoxide were used as matrix precursors. In this organic-inorganic hybrid transparent dried gel, a relative strong room-temperature photoluminescence emission at 1062 nm corresponding to the ⁴F_3/2 → ⁴I _11/2 transition of neodymium ion was measured. An intense room temperature yellow to violet upconversion emission at 398 nm was observed under a xenon lamp excitation with a yellow light at the wavelength of 580 nm, in addition to this intense violet emission, an ultraviolet emission at 345 nm and a blue emission at 470 nm were also observed. The emission mechanism is proposed, and it indicates that excited-state absorption process originating from the long-lived ⁴F_3/2 excited state should be responsible for upconversion process.