Suppression of energy transfer from Er3+ to OH− in Er3+ highly doped zirconia

We demonstrate upconversion spectra of Er3+ doped ZrO2 nanocrystals under different heat treating processes. Upconversion intensity decreases with increasing concentration of doping Er3+ when it exceeds 1 mol%. After re-calcination, however, the intensity is greatly enhanced in Er3+ highly doped samples. The mechanism of this phenomenon is attributed to the suppression of energy transfer from Er3+ to OH−. In addition, variation of the ratios of red to green emission is discussed.