Enhancement of upconversion emission in Er:LiNbO3 by codoping with HfO2 under 1550Â nm excitation

An increased red upconversion emission produced under excitation at 1550 nm was observed in hafnium and erbium co-doped lithium niobate (Hf (8 mol%)/Er:LiNbO3), which can be used to increase the photovoltaic efficiency of solar cells. Three 1550 nm photons were required to arouse the green and red emissions in Hfx(x= 2, 4, 6 mol%)/Er:LiNbO3, while the red emitting 4F9/2 state was populated by a hybrid two- and three-photon process in Hf(8 mol%)/Er:LiNbO3. The formation of Er3+ cluster sites (ErLi2+-ErNb2−) lead to an efficient cross relaxation process 4I13/2 + 4I13/2 → 4I15/2 + 4I9/2 and enhanced red emission in Hf(8 mol%)/Er:LiNbO3.