Upconversion luminescence of Ho³⁺-and Yb³⁺-codoped oxyfluride glass

Abstract

This paper studies upconversion luminescence of oxyfluoride glass codoped with holmium and ytterbium. When the sample was excited in the infrared at a wavelength of 960 nm, several visible luminescence peaks were observed. The two strongest upconversion luminescence peaks are located at 544 and 658 nm, which are due to the ⁵S₂ to ⁵I₈ and ⁵F₅ to ⁵I₈ transitions of Ho³⁺, respectively. Additional upconversion luminescence peaks are present at 485, 751, and 799 nm. The upconversion luminescence process is initiated by excitation of the codoped Yb³⁺ ions, followed by a transfer of energy from the excited Yb³⁺ ions to the Ho³⁺ ions. The dependence of the upconversion luminescence intensity with the excitation laser power obeys a power law with fractional exponent. This unusual saturation phenomenon is likely a result of energy diffusion.