Effects of pH Values on the Structure, Composition and Luminescence of CaWO₄:Tb³⁺ Thin Films

Abstract

It is hardly possible to obtain rare earth doped CaWO4thin films directly through electrochemical techniques. A two-step method has been proposed to synthesize Tb3+-doped CaWO4thin films. X-ray diffraction, energy dispersive X-ray analysis, spectrophotometer were used to characterize their phase, composition and luminescent properties. Results reveal that Tb3+-doped CaWO4films have a tetragonal phase. The ratio of n(Tb)/[n(Ca)+n(Tb)+n(Na)] decreases with the increase of pH value of TbCl3solutions. When the pH value (adjusted by NaOH) is higher than 5, Na element has been detected in CaWO4:Tb3+thin films. Based on the analysis on the composition and luminescence, it can be concluded that the pH value of TbCl3solutions must be no higher than 9.1, otherwise, no Tb3+-doped CaWO4thin films can be obtained. Under the excitation of 237 nm, sharp emission peaks at 543 and 489 nm have been observed for Tb3+-doped CaWO4:Tb3+thin films.