Up-conversion luminescence of neodymium oxalate nanoparticles/TiO₂/organically modified silane composite thin films derived at low temperature

Neodymium oxalate nanoparticles/TiO₂/organically modified silane (ormosil) composite thin films for photonic applications were prepared by a chemical approach combining the inverse microemulsion technique and the sol-gel method at low temperature. Transmission electron microscopy observation shows that the size of the neodymium oxalate nanoparticles is in the range from 10 to 40 nm. A relatively strong room-temperature violet up-conversion emission at 399 nm (⁴D_3/2 → ⁴I_13/2) has been measured from the composite thin films baked at different heat treatment temperature upon excitation with a yellow light at 587 nm. In addition to this violet emission, an UV emission at 376 nm and a blue emission at 467 nm have been obtained. The lifetimes of the violet emission have been measured and the mechanism of the up-conversion emission has been explained by means of an energy level diagram.