Blue-green upconversion emission in ZrO 2 : Yb 3 + nanocrystals

• Published in: Journal of applied physics 2008-11, Vol.104 (10), p.103508-103508-6
• Main Authors: de la Rosa, E., Solis, D., Díaz-Torres, L. A., Salas, P., Angeles-Chavez, C., Meza, O.
• Format: Article
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.3014196

Strong blue-green cooperative upconversion emission was observed under infrared excitation in 70 nm average crystallite size ZrO 2 : Yb 3 + nanocrystals prepared by sol-gel process. The structural characterization was performed by x-ray diffraction and high resolution transmission electron microscopy suggesting that crystalline phase of nanoparticles is controlled by active ion concentration. The cooperative absorption coefficient η ∼ 2.5 × 10 − 22 is four orders of magnitude larger than the ones reported from bulk crystals. The highest emission intensity was obtained from the doped sample at 4   mol % and was the result of the simultaneous relaxation of two excited Yb ions. Decay time of the upconverted signal τ CUC ≈ 0.310   ms is half from the near infrared effective decay time confirming the cooperative process among Yb ions. Such strong cooperative effect is explained in terms of interaction enhancement due to the diminishing of Yb-Yb separation promoted partly by the surface recombination of nanocrystals.