Infrared-to-green upconversion luminescence and mechanism of Ho³⁺, Nd³⁺ and Yb³⁺ ions in oxyfluoride glass ceramics

New oxyfluoride glasses and glass ceramics co-doped with Nd^3+, Yb^3+ and Ho^3+ were prepared. The upconversion of infrared radiation into green fluorescence has been studied for Nd^3+, Yb^3+ and Ho^3+ in the transparent oxyfluoride glass ceramics. At room temperature very strong green upconversion luminescence due to the Ho^3+: (^5F_4, ^5S_2)→^5I_8 transition under 800 nm excitation was observed in the glass ceramics. The intensity of the green upconversion luminescence in a 1mol% YbF_3-containing glass ceramic was found to be about 120 times stronger than that in the precursor oxyfluoride glass. The reason for the highly efficient Ho^3+ upconversion luminescence in the oxyfluoride glass ceramics is discussed. The upconversion mechanism is also investigated.