Effects of Microstructure on Photoluminescence of SrS:Eu 2+ ,SM 3+ thin Films
- PDF / 1,823,969 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 98 Downloads / 218 Views
EFFECTS OF MICROSTRUCTURE ON PHOTOLUMINESCENCE OF SrS:Eu2 +,SM3+ THIN FILMS
SUSAN Z. HUA*, L. SALAMANCA-RIBA*, M. WUTTIG* and P. K. SOLTANI** *Department of Materials and Nuclear Engineering, University of Maryland, College Park, MD 20742-2115 **Quantex Corporation, Rockville, MD 20850
Abstract 3 2 The microstructure and its effects on the photoluminescence properties of SrS:Eu +,Sm + thin films grown with different conditions were studied by transmission electron microscopy, x-ray diffraction and photoluminescence techniques. The SrS:Eu 2+,Sm3+ thin films were prepared by e-beam evaporation at different substrate temperatures and growth rates. Both of these growth conditions affect the crystallinity of the thin films. The Sm3+ emission is stronger in the films grown at higher growth rates and at an optimum substrate temperature. We believe that the stronger Sm 3 + emission is due to the higher population of Sm trivalent charge states in the films. Further increase of the substrate temperature increases the grain size in the films, but has no significant effect on the PL emission properties. In contrast, the Eu 2+ emission is less sensitive to growth conditions.
Introduction Recent developments in thin-film electroluminescence technology have renewed interest in rare-earth doped alkaline-earth sulfides in the form of thin films, because the quality of the thin films directly determines the luminescence characteristics and the performance of the devices [1, 2]. For optical memory devices, such as optically stimulated radiation dosimeters, infrared sensors and near-infrared image intensifiers, which require doubly doped phosphors, the charge states of each dopant and the probability of electronic transitions between dopants are very important. The growth conditions affect the crystallinity of the thin films and, therefore, it is expected that they also affect the emission efficiency and electron transfer processes. In order to increase the emission efficiency and improve the performance of the films, the effects of several parameters of deposition, such as substrate temperature and sulfur coevaporation, have been studied [3, 4]. However, no systematic study has been carried out on the dependence of the photoluminescence(PL) characteristics upon microstructure, and various growth parameters. In this paper, we report on the effects of growth rate and substrate temperature on the crystallinity and orientation of SrS films by transmission electron microscopy(TEM), and x-ray diffraction. The effects of microstructure on the charge states of the dopants are also studied by photoluminescence technique.
Experimental The SrS:Eu 2 +,Sm3+ thin films were deposited by the e-beam evaporation method on BaF 2 substrates [5]. In order to study the effects of growth conditions on the optical properties, the substrate temperature was varied from 500 0 C to 600 0 C, and the deposition rate was changed in the range of 15A/s to 30.A/s. The film thickness was either 2.3 Jim or 3.7pm and the Eu2 + and SmS+ concentrations were 0.002mol%
Data Loading...
