Influence of preparation atmospheres on the structural and luminescent properties of Tb-doped CaF2 thin films

Abstract

• H 2 atmosphere significantly enhanced Tb 3+ luminescence. • Air-prepared films showed cracks, larger grain sizes, and weaker emission intensity. • XPS confirmed the presence of Tb 4+ ions. The effect of preparation conditions, Ar/H 2 and air atmospheres, on structural and luminescent properties of CaF 2 :Tb thin films was investigated. The structure of the CaF 2 :Tb thin films was confirmed by X-ray powder diffraction. Cracks and big grain sizes on the thin film's surface, prepared in air atmosphere, were observed in the scanning electron microscopy images. Atomic force microscopy images for the film prepared under air atmosphere showed big particle sizes with some cracks on the surface, while a dense and smaller particle size was formed for the film prepared under Ar/H 2 atmosphere. The measured transmittance showed that the thin film prepared under Ar/H 2 exhibited slightly higher transmittance in the visible to near infrared regions. Weak emission intensity from the Tb 3+ ion with a decrease in lifetime was observed from the film prepared under air. Whereas the film prepared under an Ar/H 2 atmosphere showed a homogenous surface morphology with intense luminescence intensity from the Tb 3+ ion. The variation in the Tb 3+ : 5 D 4 lifetime was analysed using rate equation analysis. The presence of Tb 4+ ions in the thin films was confirmed by X-ray photoelectron spectroscopy. This work highlighted the importance of the preparation atmosphere on the photoluminescence properties of CaF 2 :Tb 3+ thin films.