Upconversion Luminescence of YLiF_4∶Er^(3+) Synthesized by Hydrothermal Method

摘要

YLiF4∶Er 3+ was synthesized by hydrothermal method. Concentration of Er 3+ is changed from 0 to 5%. The absorption of Er 3+ in all samples from 200 to 1200 nm was measured at room temperature. The J-O parameters calculated from absorption spectrum are Ω2=1.05×10 -20 cm2, Ω4=1.25×10 -20 cm2 and Ω6=1.35×10 -20 cm2. Infrared-to-visible upconversion emission of YLiF4∶Er 3+ was observed when excited by 980 nm. The results show that the Er 3+ content is less than 1.5%, excite-state absorption is the main mechanism of upconversion emission. When Er 3+ content is larger than 1.5%, both of the excite-state absorption and energy transfer lead to the upconversion luminescence. The upconversion intensity was enhanced with the increasing of Er 3+ concentration. At room temperature, the lifetime of 2H 11/2 and 4S 3/2 is 205 μs while that of 4F 9/2 is 188 μs for sample Er-2. The transition rates and quantum efficiency were also calculated. The quantum efficiencies of 4S 3/2 and 4F 9/2 are 27.9% and 10.7%, respectively.