Spectroscopic properties of Dy³⁺ doped ZnO for white luminescence applications

Undoped and Dy³⁺ (0.25, 0.5, 0.8 and 1.5at.%) doped ZnO were elaborated by solid-state reaction method. The ZnO:Dy³⁺ samples were characterized using X-ray diffraction (XRD), Raman spectroscopy, UV-vis diffuse reflectance spectroscopy and photoluminescence (PL). The XRD analysis confirms the wurtzite structure of ZnO. A slight shift to lower angles, of the (101) peak, is seen with Dy³⁺ content, indicating the substitution of these ions into the ZnO lattice. Raman study indicates the good crystallinity of all ZnO:Dy³⁺ samples and confirms the substitution of Zn²⁺ by Dy³⁺. The band gap energy was found to increase then decrease with Dy content. The PL excitation spectra (PLE) of Dy³⁺ showed six excitation bands with hypersensitive at 346nm (⁶H_15/2→⁶P_7/2). PL spectra show principally three emission bands relatives to ⁴F_9/2→⁶H_15/2 (476nm), ⁴F_9/2→⁶H_13/2 (567nm) and ⁴F_9/2→⁶H_11/2 (658nm) transitions. The concentration dependency of PL intensity indicates a quenching for Dy³⁺ concentration above 0.5at.%. The PL lifetime of ⁴F_9/2 metastable state was measured and discussed for all Dy content in ZnO. The temperature dependency of PL intensity is investigated for ZnO:Dy (0.5%) sample and the activation energy is determined. The CIE chromaticity color coordinate shows that ZnO:Dy³⁺ can be useful for white luminescence applications.