Emission colour tuning in KLnF4:Yb3+,Er3+/Ho3+ phosphor

Abstract

KLnF4:Yb3+,Er3+/Ho3+ (Ln = Y, Yb, Gd) phosphors were prepared by solid-state reaction technique. For each of the Yb3+/Er3+ and Yb3+/Ho3+ co-doped phosphors independently, phase confirmation and morphological examination were accomplished using the X-ray diffraction technique and scanning electron microscope analysis. X-ray photoelectron spectroscopy analysis shows the charge state and existence of lanthanides and dopants. Upconversion luminescence emissions of green and red colour were detected for the synthesized phosphors. The changes in the upconverted emission intensities and colour output pertaining to the change of the lanthanide host matrix along with dopants were investigated for the prepared phosphors. In the upconversion luminescence, erbium-doped samples exhibit a predominance of red emission while holmium-doped samples display a prevalence of green emission. The rare-earth Er/Ho doped KYbF4 shows strong red emission compared to other hosts. KYF4:Yb,Er/Ho exhibits relatively significant green upconversion emissions, while Yb,Er-doped KGdF4 host displays a 10-fold increase in green/red emission ratio with an increase in the input power of 20–780 mW. Downshifting photoluminescence studies and decay curve analysis were carried out using UV light excitation for the developed phosphors. A higher lifetime of 2.2 ms was measured for the downshifting red emission in the Ho doped KYbF4 sample. This study suggests a potential for colour tunability in the upconversion and downshifting emissions through host modifications to the fluoride phosphor.