Infrared to visible upconversion in Ho3+/Yb3+ co-doped Y2O3 phosphor: Effect of laser input power and external temperature

In the present paper, Ho3+ doped and Ho3+/Yb3+ co-doped Y2O3 phosphors have been synthesized using solution combustion technique and characterized for its structure and upconversion (UC) fluorescence as a function of Yb3+ concentration. Effect of a variation in laser input power and external temperature on the UC emission intensity has been studied to explore the UC mechanism and temperature dependent behavior of the phosphor, respectively. On excitation with near infrared (NIR) light (976 nm), the phosphor emits strong green emission along with relatively weak emission bands in red and blue regions at 553, 670 and 497 nm due to S-5(2) -> I-5(8), F-5(5) -> I-5(8) and F-5(3) -> I-5(8), respectively. The emission shows a decrease in intensity with an increase in external temperature, however contrary to the normal behavior of Ho3+, no significant change in the FIR (fluorescence intensity ratio) of F-5(4) -> I-5(8) and S-5(2) -> I-5(8) transitions is noted in the present host. This peculiar behavior of the sample with external temperature has been explained by temperature dependent lifetime study of the thermally coupled levels. (c) 2012 Elsevier B.V. All rights reserved.