Synthesis of TiO2 nanoparticles and spectroscopic upconversion luminescence of Nd3+-doped TiO2–SiO2 composite glass

Nd3+-doped TiO2–SiO2 composites were prepared by sol–gel method. Optical properties such as radiative life-time (τ), stimulated emission cross-section (σp) and branching ratio (β) were calculated using Judd–Ofelt theory. Violet to blue upconversion emissions at 380 nm (4D3/2→4I11/2), 399 nm (2P3/2→4I11/2), 420 nm (2D5/2→4I9/2) and 452 nm (2P3/2→4I13/2) were obtained under 578 nm xenon-lamp excitation. The choice of 578 nm is justified by the absorption spectra of the same samples, which shows a strong absorption peak at 578 nm. This 578 nm excitation pump produces upconversion in Nd3+ by a sequential two-photon absorption process.