To achieve a stable, sensitive, and high-efficiency biological probe, a novel NaYF_4:Yb,Er nanocrystals/TiO_2 inverse opal composite film was designed by self-assembly and solvent evaporation methods. 32-fold enhanced upconversion(UC) emission was investigated under 980 nm excitation. According to size-dependency, excitation power density-dependency as well as photonic stop band(PSB)-dependency upconversion spectra, the enhancement mechanism of the composite film was put down to the stochastical diffraction of IOPCs multi-layered structure to the excitation laser. On the basis of the enhancement effect of the composite film, energy transfer between upconversion nanoparticles(UCNPs) and quantum dots(QDs), and the sensitive sensing of CdTe QDs on mercury, the UC composite film was used for sensing of Hg^(2+) in serum. The solid sensor as a mercury detector owns lots of superiorities such as feasible operation, good linear relationship(R=0.997), low limit of detection(70.5 nmol/L) and thus may have broad prospects in the biosensing field.
Lithium lutetium fluoride(LiLuF4) single crystals doped with different Dy3+ ion concentrations were grown by Bridgman method. The Judd-Ofelt(J-O) strength parameters(Ω2, Ω4, Ω6) of Dy3+ in LiLuF4 crystal are calculated according to the measured absorption spectra and the J-O theory, by which the asymmetry of the Dy3+:LiLuF4 single crystal and the possibility of attaining stimulated emission from 4F9/2 level are analyzed. The capability of the Dy3+:LiLuF4 crystal in generating white light by simultaneous blue and yellow emissions under excitation with ultraviolet light is produced. The effects of excitation wavelength and doping concentration on chromaticity coordinates and photoluminescence intensity are also investigated. Favorable CIE coordinates, x=0.319 3 and y=0.349 3, can be obtained for Dy3+ ion in 2.701% molar doping concentration under excitation of 350 nm.
Er3+/Yb3+ codoped zincate BaGd2ZnO5 phosphors were synthesized via a traditional solid state reaction. The crystal structure and phase purity were checked by means of X-ray diffraction(XRD), and the results showed that pure phase BaGd2ZnO5 phosphors with various Er3+, Yb3+ concentrations were obtained. The influence of Er3+ and Yb3+ doping concentrations on the green and red upconversion emissions was studied. It was found that both green and red upconversion emissions under 980 nm excitation were two-photon processes independent from the rare earth doping concentrations. However, the upconversion luminescence intensities greatly depended on the rare earth doping concentration. Furthermore, the population processes of upconversion luminescence and the quenching mechanisms were analyzed. The temperature-dependent green upconversion luminescence was studied, and the temperature quenching process of two green upconversion emissions was modeled. The thermal quenching processes of the green upconversion emissions could be well explained by the model we proposed.
