MICROSTRUCTURAL STUDIES OF PHOTOLUMINESCENT THIN-FILMS OF SRS-EU2+,SM3+

A systematic study of the effect of the microstructure on the photo-lu minescence properties of SrS: Eu2+,Sm3+ thin films was carried out usi ng transmission electron microscopy, X-ray diffraction and photolumine scense techniques. The Sm3+ emission efficiency depends strongly on th e growth rate, which also affects the crystallinity of the thin films. The optimum emission of Sm3+ was obtained at growth rates of 30 angst rom/s and substrate temperature of 550-degrees-C, for which the averag e grain size is about 0.1 mum. This result can be explained by assumin g a higher population of samarium trivalent charge states in the films grown under these growth conditions. Increasing the substrate tempera ture also increases the grain size in the films, but has no significan t effect on the Sm3+ emission. However, the growth temperature affects the film's orientation. When the substrate temperature is below 550-d egrees-C, the films tend to have a (110) orientation, whereas above 55 0-degrees-C, the films are strongly oriented along the [111] direction . The brightness of the photoluminescent devices improves when the sub strate temperature is increased.