Preparation of CaS:Cu,F thin-film electroluminescent devices with an emission including purple region

CaS:Cu,F thin films have been prepared aiming at development of purple-blue emitting thin-film electroluminescent (TFEL) device with high luminance. The dependence of structural and photoluminescent (PL) properties of CaS:Cu,F thin films on annealing temperature and time was investigated. It was found that the annealing at higher than 800 °C was necessary. Moreover, improvement of crystallinity and PL properties of the films saturated for the annealing time longer than 10 min. It is concluded, therefore that the annealing at higher than 800 °C for about 10 min is desirable. CaS:Cu,F TFEL devices was fabricated on Si substrate. The purple-blue EL with an obvious peak at 425 nm was obtained from the device with 0.3 at.% of Cu for the first time.