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The red-emitting Ca9Eu(PO4)7 nanophosphors have been successfully synthesized by a facile hydrothermal method. X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, GSAS structural refinement and scanning electron microscopy (SEM) were used to characterize the materials. Rietveld refinement of powder X-ray diffraction patterns of Ca9Eu(PO4)7 demonstrated that the structure of Ca9Eu(PO4)7 consisted of [PO4] tetrahedra. Ca/Eu atoms filled the space between the tetrahedral groups with Eu3+ ions distributed randomly on three individual Ca crystallographic sites. The major red emission peak located at 616 nm under 397 nm excitation attributed to the electric dipole transition 5D0→7F2 of Eu3+ was a parity forbidden f–f configuration transition, which would only occur when Eu3+ occupied lattice sites without inversion symmetry. Introducing Gd, La, and Y ions into samples made luminescence properties of Ca9Eu1−xLnx(PO4)7 (Ln = Gd, La, Y) phosphors decrease. pH value plays a key role in the formation of Ca9Eu(PO4)7 nanophosphor morphology. With increasing pH in the initial reaction solution, the morphology of samples changed from rod to sphere and their aspect ratio also decreased. Different morphologies have different photoluminescence properties, and samples prepared at pH 7 manifested better photoluminescence properties relative to other samples. This novel red-emitting phosphor could be applied in white light-emitting diodes. [ABSTRACT FROM AUTHOR]

A novel phosphate Ca9La(GeO4)0.75(PO4)6 was investigated to add to the family of phosphate phosphors and application in LEDs. In this work, the single phase red-emission Ce3+,Mn2+ co-doped phosphate Ca9La(GeO4)0.75(PO4)6 phosphor was synthesized by the solid-state reaction from both theoretical and practical points of view. The crystal structure was determined by Rietveld refinement and TEM. Its cell parameters are a = b = 10.4077605(2) Å, and c = 37.4714968(1) Å. The characteristic photoluminescence properties were studied in detail using photoluminescence excitation spectra, emission spectra, decay times and thermal quenching properties. Purple and red broad band emission from Ce3+ and Mn2+ was detected under excitation at 313 nm. According to this research, the Ca9La(GeO4)0.75(PO4)6:Ce3+,Mn2+ phosphor shows high thermal stability in the red-emission area. With the increase of the temperature, the intensity ratio of Mn2+ and Ce3+ emission rises rapidly and the purity of red-emission is improved. In order to reasonably explain this special phenomenon, an implicit mechanism between thermal quenching and energy transfer is proposed based on the configurational coordinate diagram. In addition, the mechanism could be helpful for understanding the thermal properties of multiple activators Ce3+ and Mn2+ co-doped phosphors as the reference. [ABSTRACT FROM AUTHOR]