Up-conversion luminescence of Er^(3+) doped and Er^(3+)/Yb^(3+) co-doped YTaO_4

The synthesis and up-conversion luminescent properties of YTaO4:Er3+ and YTaO4:Er3+/Yb3+ are re- ported for the first time. According to the measurement results of up-conversion spectra, Yb3+ co-doping can remarkably enhance the green (2H11/2/4S3/2→4I15/2) and red (4F9/2→4I15/2) emissions, but de- press the infrared emission (4I9/2→4I15/2). With the increase of the Yb3+ concentration, the intensity of green emission increases, after that, when the Yb3+ concentration increases continuously, the intensity of green emission decreases, while those of the red and infrared emissions increase and decrease alternately. In addition, the up-conversion mechanisms of Er3+ doped and Er3+/Yb3+ co-doped YTaO4 are also discussed. It is found that the transform of up-conversion mechanism from two-step energy transfer to cooperating sensitization takes place when Yb3+ concentration is increased up to 12 mol%. With the further increase of Yb3+ concentration, the energy-back-transfer gradually becomes the dominant up-conversion mechanism, which results in the quenching of the green emission and slight increasing of the red and infrared emissions.