Highly efficient green up-conversion luminescence of Nd3+–Yb3+–Ho3+ codoped fluorite-type nanocrystals in transparent glass ceramics

Oxyfluoride glasses were developed with composition 30SiO2⋅15AlO1.5⋅28PbF2⋅22CdF2⋅(4.8−x)GdF3⋅0.1NdF3⋅0.1HoF3⋅xYbF3 (x=0, 0.1, 0.2, 0.5, 1, 2, 3, 4, and 4.8) in mole percent. Powder x-ray diffraction analysis revealed that the heat treatments of the oxyfluoride glasses at 450 °C for 0.5 h cause the precipitation of Nd3+–Yb3+–Ho3+ codoped fluorite-type nanocrystals of about 16.3 nm in diameter in the glass matrix. These transparent glass ceramics exhibited very strong green up-conversion luminescence due to the Ho3+: (5F4, S25)→5I8 transition under 800 nm excitation. The intensity of the green up-conversion luminescence in a 1 mol % YbF3-containing glass ceramic was found to be about 120 times stronger than that in the precursor oxyfluoride glass. The reason for the highly efficient Ho3+ up-conversion luminescence in the oxyfluoride glass ceramics is discussed. An up-conversion mechanism is also proposed.