Yellow-green-emitting Sr Si2O2N2:Eu2+phosphors were synthesized with Sr2Si O4:Eu2+as precursor.The effects of flux and the concentration of Eu2+on the crystal structure and luminescent properties of the phosphors were investigated.Results suggested that the optimal content of flux Na2CO3 was 1 wt%and the optimal doping concentration of Eu2+was 0.05 mol.The emission spectra showed the most intense peaks located at 535 nm which corresponded to the 4f65d→4f7 transition of Eu2+.The excitation spectra showed that these phosphors could be effectively excited by near-ultraviolet and blue light,whichwas consistent with the widely applied output wavelengths of near-ultraviolet and blue-white light-emitting diode(LED)chips.When the influence of flux on the luminescent properties of Sr Si2O2N2:Eu2+phosphor was analyzed,the X-ray diffraction(XRD)patterns indicated that the flux could help the crystallization of the phosphors.No other phases except the triclinic structure of Sr Si2O2N2 were formed.The thermal stability and the emission intensity of synthesized Sr Si2O2N2:Eu2+phosphor were examined and compared with commercial YAG yellow phosphors.All results indicate that the yellow-green-emitting phosphor is a suitable candidate for the fabrication of white LEDs.
Ce^(3+), Tb^(3+) doped orthorhombic phases of KLu_2F_7 microcrystals with hexagonal disk morphology were synthesized by a hydrothermal method. Enhanced emissions of Tb^(3+) were observed in the Ce^(3+)/Tb^(3+) co-doped KLu_2F_7 sample compared to the Tb^(3+) single-doped KLu_2F_7. The energy transfer efficiency from Ce^(3+) to Tb^(3+) was calculated by the photoluminescence intensity in the Ce^(3+)/Tb^(3+) co-doped KLu_2F_7 samples. The average separations between Ce^(3+) and Tb^(3+) were calculated and the critical distance was 0.922 nm estimated by method of concentration quenching. The theoretical calculation proved the results. The theoretical analysis also suggested that the energy transfer from Ce^(3+) to Tb^(3+) in the KLu_2F_7 occurred predominantly via the dipole-quadrupole interaction. The KLu_2F_7 should be good host materials for emitters.
By controlling the reactant ratios, hydrothermal time, hydrothermal temperatures, p H values of the prepared solutions, and the concentrations of K3C6H5O7·2H2O, 1 mol% Eu3+ doped cubic phase of K5Gd9F32 and/or orthorhombic phase of Gd F3 micro/nanocrystals have been synthesized based on a hydrothermal method. For comparison, the sample was also synthesized by a co-precipitation method. The samples were characterized by X-ray diffraction(XRD) patterns, field emission scanning electron microscopy(FE-SEM) images, energy-dispersive spectroscopy(EDS) spectra, and photoluminescence(PL) excitation and emission spectra. By host Gd3+ sensitizing, the Eu3+ presents relatively strong emissions. The energy transfers from host Gd3+ to doping Eu3+ are observed in all the samples and the energy transfer plays an important role in the emission of Eu3+. Acting as a probe, the Eu3+ presents its distinct optical properties in the samples.
