Microstructural studies of photoluminescent thin films of SrS: Eu²⁺, Sm³⁺

A systematic study of the effect of the microstructure on the photo-luminescence properties of SrS: Eu²⁺, Sm³⁺ thin films was carried out using transmission electron microscopy, X-ray diffraction and photoluminiscense techniques. The Sm³⁺ emission efficiency depends strongly on the growth rate, which also affects the crystallinity of the thin films. The optimum emission of Sm³⁺ was obtained at growth rates of 30 Å/s and substrate temperature of 550{ring operator}C, for which the average grain size is about 0.1 μm. This result can be explained by assuming a higher population of samarium trivalent charge states in the films grown under these growth conditions. Increasing the substrate temperature also increases the grain size in the films, but has no significant effect on the Sm³⁺ emission. However, the growth temperature affects the film's orientation. When the substrate temperature is below 550{ring operator}C, the films tend to have a (110) orientation, whereas above 550{ring operator}C, the films are strongly oriented along the 〈111〉 direction. The brightness of the photoluminescent devices improves when the substrate temperature is increased.