Nature Photonics Research Highlight: Upconversion nanocrystals

Appl. Phys. Express 5, 092601 (2012)

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Lanthanide-doped nanocrystals that can efficiently upconvert infrared radiation into visible light are being studied with a view to applying them in the display, DNA-detection and bio-imaging areas. Now Xiaojie Xue and co-workers from the Toyota Technological Institute, Japan have observed ultraviolet emission from Tb3+/Yb3+ co-doped KY3F10 nanocrystals that were excited with light from a 976-nm laser diode. KY3F10 nanocrystals doped with x% Tb3+ and 5% Yb3+ were synthesized by a hydrothermal method and had an average size of about 45 nm. The emission spectrum of the nanocrystals featured both strong ultraviolet emission at 381 nm and weaker green emission at 544 nm. The emission decay time for the ultraviolet emission was 1.9 ms. The intensity ratio between the ultraviolet–blue emission from the 5D3 level and the green emission from the 5D4 level decreased with increasing Tb3+ concentration. The researchers say that this concentration-dependent phenomenon is evidence of cross-relaxation, and indicates possible upconversion mechanisms based on the energy transfer from Yb3+ to Tb3+ and cross-relaxation processes between Tb3+ pairs