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The synthesis and component of red phosphor, Sr4Al14O25: Mn, were optimized for application in white light-emitting diodes. The microstructure and morphology were investigated by the X-ray diffraction and scanning electron microscopy. Different valences of Mn ions in Sr4Al14O25 were discriminated using the electron paramagnetic resonance and X-ray absorption near-edge structure spectroscopy techniques. The bond-valence theory was used to analyze the effective valences of Sr2+ and Al3+ in Sr4Al14O25. As a result, the strong covalence of Al3+ in the AlO4 tetrahedron other than in the AlO6 octahedron is disclosed. The deep red emission is attributed to Mn4+ occupying the center of AlO6 octahedron. The mechanism of energy transfer is mainly through dipole–dipole interaction, revealed by the analyses of critical distance and concentration quench. A high color rendering white LED prototype with color-rendering index up to Ra 93.23 packaged by using the red phosphor demonstrates its applicability.

The phosphors of Sb3+ and Eu3+ activated YBO3 were synthesized via solid-state reaction. The crystal structure was investigated using X-ray diffraction analysis. The luminescence and energy transfer were investigated on the synchrotron radiation instrument, by exciting with different wavelengths at room temperature or as low temperature as 14 K. The electron-lattice interaction between the activator Sb3+ and the host of YBO3 combined with the spin-orbit interaction of Sb3+ result in a large Stokes shift in Sb3+ emission, giving rise to no matchable energy levels for the energy transfer from Sb3+ to Eu3+. Nevertheless, the excitation energy could transfer from Bi3+ to Eu3+, which has the same ns(2) electronic configuration as Sb3+. Taking advantage of the simultaneous isolated luminescence of Sb3+ and Eu3+, finally, the white luminescence from a single phosphor was tuned up by tailoring Sb3+ and Eu3+ concentrations in the YBO3 host, which shows potential application in deep ultraviolet light-emitting diodes (LEDs). (C) 2014 Elsevier B.V. All rights reserved.

This study provides an explanation for the mechanism of carbothermal reduction contributing to the synthesis of a Sr2Si5N8 : Eu2+ nitride phosphor, in terms of the heat released and propagated within the local region, which makes the actual temperature far higher than that determined in the reaction. Two pathways of carbon mixing were designed for synthesizing SrSi2O2N2 : Eu2+ at relatively lower temperatures than that required for synthesis of Sr2Si5N8: Eu2+. However, formation of the nitride, Sr2Si5N8 : Eu2+, was observed by mixing carbon with the raw materials, rather than placing a layer of carbon underneath for heat conduction, indicating that close contact of carbon with the raw materials was a precondition of nitride formation. In addition, the presence of an amorphous layer on the surface of the phosphor particles, identified using a high-resolution transmission electron microscope, provided a clue to understanding the mechanism of the nitridation reaction at relatively low temperatures.

To enhance the luminescence of (Sr,Ba) 3 SiO 5 :Eu 2+ for white light-emitting diodes, a new method for the synthesis of phosphor was developed. In the proposed method, the mixture of large and nano SiO 2 particles as a silica source was employed to control the nucleation and crystal growth of the material. The impurity phase (Sr,Ba) 2 SiO 4 , which easily coexisted with (Sr,Ba) 3 SiO 5 was suppressed. Accordingly, the luminescence was enhanced significantly by the partial substitution of conventional SiO 2 with nano SiO 2 . The improvement in crystallinity and morphology was examined with XRD and SEM. Moreover, the sintering temperature and the concentration of nano SiO 2 was optimized. The results show that appropriate amount of nano SiO 2 has pronounced effects on the nucleus formation and crystal growth, while excessive crystal seeds formed may hinder the growth of particles. A mechanism for this improvement was proposed.