* Corresponding author. Tel.: #1-404-894-0109; fax: #1- 404-894-5073. E-mail address: won.park@gtri.gatech.edu (W. Park) Journal of Luminescence 87}89 (2000) 1267}1270 A spectroscopic study on SrS : Cu,Ag two-component electroluminescent phosphors W. Park*, T.C. Jones, C.J. Summers Phosphor Technology Center of Excellence, Manufacturing Research Center, Georgia Institute of Technology, 813 Ferst Drive, Atlanta, GA 30332-0560, USA Abstract Under 4.507 eV excitation, the SrS : Cu,Ag thin "lms exhibited a saturated blue emission at 2.876 eV at room temperature and two additional emission bands at 3.443 and 2.398 eV were also observed at 10 K. By comparing with singly doped SrS : Cu and SrS : Ag, the two bands at 3.443 and 2.876 eV were assigned to the Ag emission bands and the 2.398 eV band to Cu emission. The enhancement of the 2.876 eV Ag emission band and the simultaneous suppression of the 2.398 eV Cu emission band are indicative of the presence of strong energy transfer from Cu to Ag ions in SrS : Cu,Ag. Low-temperature PLE spectrum of the 2.876 eV emission band was found to exhibit Cu excitation bands, con"rming the presence of energy transfer from Cu to Ag. However, the energy transfer process from Cu to Ag exhibited anomalous properties that cannot be explained by the standard energy transfer theory. Therefore, instead of a Dexter-type energy transfer, electron transport was proposed as a possible coupling mechanism between the Cu and Ag ions in SrS.  2000 Elsevier Science B.V. All rights reserved. Keywords: SrS : Cu,Ag; Electroluminescence; Photoluminescence; Energy transfer One of the most exciting developments in electro- luminescent (EL) phosphors in recent years was the de- velopment of SrS : Cu,Ag two-component phosphors [1]. This development was preceded and motivated by the discovery that SrS : Cu exhibited e$cient EL emis- sion with a good blue chromaticity [2]. The broad emis- sion of SrS : Cu centered at 2.61 eV was attributed to the 3d4sP3d ionic transition of the Cu ion occupying the Sr site with an octahedral symmetry. A "ne structure was also observed in the excitation spectrum of the Cu emission and was studied by using crystal-"eld theory [3,4]. The success of SrS : Cu naturally directed attention to SrS : Ag, which has the same outer shell electronic structure. Despite the fact that SrS : Ag exhibits a strong and highly saturated blue emission centered at 2.88 eV under optical excitation, the EL performance was very poor [5]. Therefore, a new system, SrS : Cu,Ag, was de- signed to take advantage of both the good chromaticity of Ag and the high excitation e$ciency of Cu. It was observed that SrS : Cu,Ag exhibits an e$cient and highly saturated blue emission under both optical and EL exci- tation conditions. The previous study on SrS : Cu,Ag by photoluminescence (PL) and PL excitation (PLE) spec- troscopy con"rmed the existence of an e$cient energy transfer path from Cu to Ag [1]. Furthermore, the e$- cient coupling between Cu and Ag was also evident under EL excitation. A detailed study of the EL charac- teristics of SrS : Cu,Ag showed that the excitation char- acteristics of SrS : Cu,Ag were consistent with those of SrS : Cu while the emission characteristics were identical to that of SrS : Ag [6]. The success of SrS : Cu,Ag opens a pathway to develop a new class of phosphors consisting of two components, the sensitizer with a high excitation probability and the activator with a good chromaticity. The success of the two-component phosphor depends critically on the e$cient coupling between the sensitizer and the activator. Therefore, it is of fundamental impor- tance to understand the coupling mechanism. In this 0022-2313/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 2 3 1 3 ( 9 9 ) 0 0 5 5 6 - 6