Light fantastic! Lu2O3:Yb3+/Er3+/Tm3+ nanocrystals with controllable red, green, blue (RGB) and bright white upconversion luminescence by a single laser excitation of 980 nm have been successfully synthesized (see picture). Due to abundant UC PL colors, it can potentially be used as fluorophores in the field of color displays, back light, UC lasers, photonics, and biomedicine.
Lu2O3:Yb3+/Er3+/Tm3+ nanocrystals have been successfully synthesized by a solvothermal process followed by a subsequent heat treatment at 800 °C. Powder X-ray diffraction, transmission electron microscopy, upconversion photoluminescence spectra, and kinetic decay were used to characterize the samples. Under single-wavelength diode laser excitation of 980 nm, the bright blue emissions of Lu2O3:Yb3+, Tm3+ nanocrystals near 477 and 490 nm were observed due to the 1G4→3H6 transition of Tm3+. The bright green UC emissions of Lu2O3:Er3+ nanocrystals appeared near 540 and 565 nm were observed and assigned to the 2H11/2→4I15/2 and 4S3/2→4I15/2 transitions, respectively, of Er3+. The ratio of the intensity of green luminescence to that of red luminescence decreases with an increase of concentration of Yb3+ in Lu2O3:Er3+ nanocrystals. In sufficient quantities of Yb3+ with resprct to Er3+, the bright red UC emission of Lu2O3:Yb3+/Er3+ centered at 662 nm was predominant, due to the 4F9/2→4I15/2 transition of Er3+. Based on the generation of red, green, and blue emissions in the different doped Lu2O3:RE3+ nanocrystals, it is possible to produce the luminescence with a wide spectrum of colors, including white, by the appropriate doping of Yb3+, Tm3+, and Er3+ in the present Lu2O3 nanocrystals. Namely, Lu2O3:3 %Yb3+/0.2 %Tm3+/0.4 %Er3+ nanocrystals show suitable intensities of blue, green, and red (RGB) emission, resulting in the production of perfect and bright white light with CIE-x=0.3456 and CIE-y=0.3179, which is very close to the standard equal energy white light illuminate (x=0.33, y=0.33). Because of abundant luminescent colors from RGB to white in Lu2O3:Yb3+/Er3+/Tm3+ nanocrystals under 980 nm laser diode (LD) excitation, they can potentially be used as fluorophores in the field of color displays, back light, UC lasers, photonics, and biomedicine.