Effect of the CTAB concentration on the upconversion emission of ZrO2:Er3+ nanocrystals

Upconversion emission of ZrO2:Er3+ (0.2 mol%) nanophosphor were studied as function of surfactant concentration after excitation at 968 nm. The strong green emission was produced by the transition 2H11/2 + 4S3/2 → 4I15/2 and was explained in terms of cooperative energy transfer between neighboring ions. The upconverted signal was enhanced but the fluorescence decay time was reduced as either the surfactant concentration increases or the annealing time reduces. Experimental results show that surfactant concentration controls the particle size and morphology while annealing time control the phase composition and crystallite size. The highest intensity was obtained for a sample composed of a mixture of tetragonal (33 wt.%) and monoclinic (67 wt.%) phase with crystallite size of 31 and 59 nm, respectively. This result suggests that tetragonal crystalline structure and small crystallite size are more favorable for the upconversion emission.