Temperature induced upconversion behaviour of Ho3+-Yb3+ codoped yttrium oxide films prepared by pulsed laser deposition

Pulsed laser deposited Ho3+-Yb3+ codoped yttrium oxide films were grown on silicon substrates in vacuum at different substrate temperatures (373, 573, 773 and 973 K). The deposited films have shown a phase transition on increasing the substrate temperature, as confirmed by the X-ray diffraction analysis. The grain distribution and surface roughness of the deposited thin films have been estimated by atomic force microscopy measurements. In the optical properties study upconversion luminescence at 547, 656 and 758 nm was revealed upon 980 nm excitation. 773 K was found to be the best substrate temperature owing to the thickest deposited layer, as indicated by Auger depth profile analysis of the prepared films. A non-tunable bright green upconversion emission due to the involvement of a two photon process was established and a possible excitation-emission mechanism is explained by using an energy level diagram of the dopant ions.