The effect of post-thermal annealing on photo- and infrared-stimulable CaS : Eu,Sm thin films

Abstract

CaS : Eu,Sm thin films were deposited using the rf magnetron sputtering technique. XRD studies demonstrated a great improvement in the crystalline structures of CaS : Eu,Sm thin films after post-thermal annealing, which also led to an increase in the refractive index of CaS : Eu,Sm thin films. The photoluminescence (PL) and infrared-stimulated luminescence (ISL) of CaS : Eu,Sm thin films were thereby detected. The ISL emission spectra of CaS : Eu,Sm thin films demonstrated that ISL occurred due to the recombination of de-trapped electrons from occupied electron trapping centres (Sm2+) and previously ionized luminescent centres (Eu3+). It was found that the PL and ISL of CaS : Eu,Sm thin films were greatly enhanced due to depression of defects and sulfur deficiencies by using sulfur vapour in the post-thermal annealing processes. The readout test showed that it took tens of seconds to empty the trapped electrons at the electron trapping sites formed in the CaS : Eu,Sm thin films until the ISL disappeared under continuous infrared stimulation.