Lanthanide doping in ZnS and SrS thin-film electroluminescent devices

The relative high field transport efficiency and short wavelength electroluminescence (EL) potential of the phosphors ZnS and SrS for alternating-current thin-film electroluminescent (ACTFEL) device flat-panel display applications are assessed via a comparison of the EL spectra of ZnS and SrS ACTFEL devices prepared in a very similar manner and doped with the same lanthanide luminescent impurities: Dy, Er, Ho, Tb, and Tm. For all of the lanthanide luminescent impurities studied, it is found that the the higher energy EL peaks are much more intense for SrS than for ZnS, even though the average phosphor field in SrS is smaller than in ZnS. These observations show SrS to be a superior high-field electron transport material compared to ZnS. All of the ZnS EL spectra show a dramatic cut off in their EL intensities at about 440-460 nm; this suggests that ZnS is not an appropriate phosphor for blue light emission since its electron distribution does not appear to be adequately heated to efficiently excite blue luminescent impurities. (C) 1999 American Institute of Physics. [S0021-8979(99)07324-7].