Upconversion for enlarging solar spectrum response in near-stoichiometric and congruent Er:LiNbO3 crystals

Abstract To increase the photovoltaic efficiency of solar cell, the visible luminescence produced at the excitation of the near infrared laser light in near-stoichiometric and congruent LiNbO3 crystals heavily doped with Er3+ ions (Er:NSLN and Er:CLN, respectively) were investigated. An enhancement of the green upconversion emission observed in Er:NSLN crystal was attributed to the inefficient cross relaxation processes of 2H11/2 + 4I13/2 → 4I11/2 + 4F9/2 and 4F7/2 + 4I11/2 → 4F9/2 + 4F9/2. The Er content in the crystal was measured by an inductively coupled plasma mass spectrometry (ICP-MS). The OH− absorption and UV–vis-near infrared absorption spectra indicated that the Er3+ cluster sites ( Er Li 2 + – Er Nb 2 - ) were dissociated in Er:NSLN crystal. The strong green upconversion emission produced by Er:NSLN crystal will be beneficial for improving the practical performance of solar cells.