Co-doping size-tunable SnO2 nanocrystals into Er(3+) ions embedded silica thin films produces an enhancement of Er-related near-infrared emission by three orders of magnitude. Selective PL and PLE measurements show that energy transfer process occurs between SnO2 nanocrystals and Er(3+) ions. Quantitative studies of PL decay lifetime and photoluminescence temperature-dependence demonstrate that both high energy transfer efficiency from SnO2 nanocrystals to Er(3+) ions and the partial incorporation of Er(3+) ions into SnO2 nanocrystals contribute to the near-infrared emission enhancement. All these results indicated that SnO2 nanocrystals with suitable size have great potentials in fabricating high-efficiency near-infrared luminous materials as sensitizers of Er(3+) ions.

NaYF4:Yb,Er nanocrystals with different concentrations of Gd3+ ions are prepared via a hydrothermal method.

Usually, up-conversion (UC) green emission is easily observed by using rare-earth doped fluoride nanocrystals. However, preferential red emission is desired for some actual applications especially in biological field. Here, we demonstrated that the dominant UC red emission can be realized by preparing TiO:Yb,Er nanocrystals under 980 nm exciation. By controlling the crystal symmetry and size via the annealing temperature and Yb ions concentration, the enhanced UC red emission is achieved. The multi-photon relaxation and cross-relaxation mechanisms may be responsible for the energy transform process and in turn the UC emission.

Er(3+) ions and SnO2 nanocrystals co-doped silica thin films are prepared by an improved sol-gel spin-coating method. With increase in annealing temperature, the related 1.54 μm characteristic emission intensity from Er(3+) ions is obviously enhanced by more than two orders of magnitude via SnO2 nanocrystals size control to boost the sensitization efficiency. Quantitative studies of steady-state spectroscopic data and fluorescence decay curves demonstrate that the related sensitization efficiency via size-tunable nanocrystals is increased from 0.14% to 1.3%. This improved sensitization efficiency is achieved by doping some of the Er(3+) ions into the SnO2 inner sites at a high annealing temperature, as revealed by high-resolution TEM, X-ray diffraction patterns and elemental mapping technique. Different sensitization mechanisms are also discussed separately according to the selective photoluminescence excitation measurements. All these results have not only explained the greatly improved sensitization efficiency resulting from SnO2 nanocrystals but also indicated that the development of Er(3+) ions and SnO2 nanocrystals co-doped silica thin films could result in promising high-performance near-infrared luminous materials using broadband UV pumping.