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

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.