Preparation and optical properties of sol–gel neodymium-doped germania/γ-glycidoxypropyltrimethoxysilane organic–inorganic hybrid thin films

Abstract

Germania/γ-glycidoxypropyltrimethoxysilane organic–inorganic hybrid spin-coating thin films doped with neodymium ions are prepared by a sol–gel technique and a spin-coating process. Acid-catalyzed solutions of γ-glycidoxypropyltrimethoxysilane mixed with germanium isopropoxide are used as matrix precursors. Thermal gravimetric analysis, UV–visible spectroscopy, and Fourier transform infrared spectroscopy are used to study the structural and optical properties of the hybrid thin films. The results indicate that films that are crack-free and have a high transparency in the visible and near-infrared range can be obtained; a strong UV absorption region at short wavelength ∼200 nm, accompanied with a shoulder peaked at ∼240 nm, due to the neutral oxygen monovacancy defects, is also identified. Upconversion emission properties of the transparent dried gel and the thin films heated at different heat treatment temperatures and doped with different neodymium ion concentrations are studied; a relatively strong room-temperature yellow to violet upconversion emission at 397 nm (4D3/2→4I13/2) is observed under a xenon lamp excitation with yellow light at the wavelength of 580 nm (4I9/2→4G5/2). The effect of Nd3+ doping concentration and heat treatment temperature on upconversion emission of the thin films is also studied. The mechanism of the upconversion is proposed.