CaS:Eu,Sm films prepared by pulsed laser deposition

Abstract

Electron trapping thin films CaS:Eu,Sm have been deposited by pulsed laser deposition in vacuum and simultaneous sulfur coevaporation. The films prepared by doubly rare-earth ions doped alkaline earth sulfides CaS have the characteristics of infrared upconversion and optical storage. Its phases and microstructures were identified by X-ray diffraction. The chemical composition of the films was determined by secondary ion mass spectrum. The studies on the optical properties of the films show they can convert the infrared light (800 - 1600 nm) to red light (approximately 672 nm). Infrared upconversion efficiency of CaS:Eu,Sm thin films with different thickness has been investigated by using the ultrashort infrared laser with different FWHM from microsecond(s) to ps. It is shown the upconversion efficiency of CaS:Eu,Sm thin films not only depends on the growth conditions and the post annealing process, but also has the `exhaustion' phenomenon. By means of measuring transmittance and spatial resolution of CaS:Eu,Sm thin films, the post annealing process was found to promote grain growth which could obviously improve upconversion efficiency of CaS:Eu,Sm thin films, even though it had negative influence on transmittance and spatial resolution of CaS:Eu,Sm thin films.