Preparation of Sr2CeO4 blue phosphor by ultrasonic spray pyrolysis: effect of NH4NO3 addition

A blue emission Sr₂CeO₄ phosphor powder which has a one-dimensional structure was prepared from a nitrate starting solution by the ultrasonic spray pyrolysis process. To avoid the formation of hollow particles during spray pyrolysis, NH₄NO₃ was employed to change the mechanism of Sr₂CeO₄ formation from droplets, containing Sr(NO₃)₂ and Ce(NO₃)₃ in the required stoichiometric ratio. The mean particle size of as-prepared particle increased from 0.19 to 1.52 m with a change in the overall concentration of the starting solution from 0.005 to 1.5 M. No hollow particles or particle fragments were observed when the ratio of overall concentration of the starting solution to NH₄NO₃ was equal to 1 : 1. The particles that were as-prepared with NH₄NO₃ had spherical morphology and a narrow size distribution. The emission spectrum of post heat-treated particles showed a broad maximum at 470 nm and the CIE Chromaticity coordinates were x = 0.20 and y = 0.27. The decay time of Sr₂CeO₄ phosphor powder was 58 s, which is a long excited-state life time compared with d-f transitions for the Ce³⁺ excited state.