Er3+ doped and Er3+/Yb3+ co-doped superfine LaF3 powders are prepared using co-precipitation method. The sample shows spherical particles with size of about 250 nm. The quantum efficiencies of 4S3/2 and 4F9/2 levels in the prepared Er3+ doped LaF3 powders are calculated to be 67.0% and 71.9%, respectively. With the enhancement of the Yb3+ doping concentration, The upconvertion intensity increases as a function of excitation power more slowly due to the enhancement of the sensitization of Yb3+ to Er3+. The Er3+-Er3+ interaction is also reinforced as the Yb3+ concentration increases. This leads to the increase of the ratio of the green emission to the red one with the enhancement of Yb3+ concentration.
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