Upconversion emissions induced by 1550 nm in near-stoichiometric Er:LiNbO3 crystal

To increase the photovoltaic efficiency of solar cells, green and red upconversion (UC) emissions produced at an excitation of 1550 nm were investigated. A drastically enhanced red UC emission was observed in near-stoichiometric LiNbO(3) crystal heavily doped with Er(3+) ions (Er:NSLN). Raman spectra showed that the maximum phonon energy shifted from 631 cm(-1) in Er(3+)-doped congruent LiNbO(3) (Er:CLN) to 871 cm(-1) in Er:NSLN crystal. The time decay of the (4)S(3/2)→(4)I(15/2) transition suggested that the Er(3+) cluster sites (Er(Li)(2+)-Er(Nb)(2-)) were dissociated in the Er:NSLN crystal. The visible UC luminescence converted from near infrared at the wavelength of 1550 nm was important to enlarge the solar spectrum response of solar cell.