Energy Transfers And Chromatic Properties Of Rare Earth Ions Doped Scheelite Structured Molybdate Phosphors

In recent years, rare earth ions doped phosphors have attracted much attention and have been applied in fields such as lighting sources, displays and biological labeling because of their outstanding luminescent properties. Amongst all the luminescent materials, molybdates with scheelite structure, as the host of the phosphors, have evoked much interest because of their excellent optical properties, chemical stability, and physical stability which are beneficial to the luminescent performance. In this paper, we mainly study the luminescent and chromatic properties of the Dy3+ single-doped Gd2Mo3O9 phosphors, Dy3+, Sm3+, Er3+ single-doped and Dy3+-Sm3+ co-doped NaGd(MoO4)2 phosphors.Rare earth ions doped molybdate phosphors were synthesized via the conventional solid-state reaction method. Their crystal structures, spectroscopic properties, energy transfers and chromatic properties were characterized with XRD, optical spectroscopy, concentration quenching curve fitting, decay lifetime curve fitting and color coordinates.First, the influence of reaction temperature and Dy3+-doping concentration on the crystal structure of the Dy3+ single-doped molybdates phosphors was examined with XRD. The optimal reaction temperature was found out for the synthesis of the samples with various doping concentrations. Through measuring the fluorescence spectra of the samples, the influence of the Dy3+-doping concentration on luminescent properties was found and the energy transfers in the spectra were also discussed. Based on the Van Uitert’s mode the concentration quenching behavior of Dy3+ fluorescence was studied, and the D-D interaction between Dy3+ ions was found to be the main physical mechanism, which is also in accordance with the conclusion derived from fluorescence decay lifetime curve analysis. Finally, the influence of Dy3+ doping concentration on color coordinates was analyzed.Second, the influence of the Sm3+-doping concentration on luminescent properties was presented through measuring the fluorescence spectra. Based on the energy levels of Sm3+ and the energy match rule, the possible cross relaxation channels among Sm3+ ions were revealed. Finally, the dependence of color coordinates on the Sm3+ doping concentration was studied.Third, the spectral properties of Dy3+-Sm3+ co-doped NaGd(MoO4)2 phosphors were studied according to the fluorescence spectra. The energy transfer behaviors among Dy3+, Sm3+ and host were also found from the quotient spectra. Based on the energy levels of Sm3+ and Dy3+, the possible cross relaxation channels were analyzed. It was in accordance with our desired result that the samples had a good red component by use of introducing the Sm3+ ions.Finally, in this paper, the up-conversion and down-conversion spectral properties of Er3+ single-doped NaGd(MoO4)2 phosphors were all studied. The down-conversion spectral properties of Er3+ were researched. The influence of the up-conversion emission intensity on the working current and doping concentration were detected. The multi-photon processes of the red and green emissions were analyzed. In addition, the color coordinates of the up-conversion and down-conversion spectra were compared and discussed.