Chongfeng Guo

Efficient red phosphors Na5Ln(MoO4)4 : Eu3+ (Ln = La, Gd and Y) for white LEDs

A class of red-emitting phosphors Na5Ln(MoO4)4 : Eu3+(Ln = La, Gd and Y) have been synthesized by the sol–gel technique and their luminescent properties have also been investigated under the near-ultraviolet (n-UV) light. The excitation spectra of these phosphors show the strongest absorption at about 395 nm which matches well with the commercially available n-UV-emitting GaN-based LED chip. Their emission spectra show intense red emission at 618 nm due to the 5D0–7F2 transition of Eu3+. The phosphor Na5Y1−xEux(MoO4)4 shows the brightest red light among phosphors Na5Ln1−xEux(MoO4)4 as the content of Eu3+ is fixed. In addition, the conditions for synthesis of these phosphors are also optimized, including annealing temperature and concentration of Eu3+ ions. While the Li+ or K+ ions are incorporated into Na5Eu(MoO4)4 to substitute for Na+ partially, effects on the luminescent properties and structures of phosphors have also been discussed in detail.

A Dual-Emission Phosphor LiCaBO3 : Ce3 + , Mn2 + with Energy Transfer for Near-UV LEDs

A series of Ce 3+ and Mn 2+ co-doped LiCaBO 3 single composition phosphors were synthesized by a solid-state reaction method, and their luminescent properties had also been investigated. Ce 3+ and Mn 2+ co-doped LiCaBO 3 phosphors showed a blue and orange dual emission under the near-UV light excitation within the wavelength range of 325-375 nm, resulting from the 5d-4f transitions of Ce 3+ and the d-d forbidden transition of Mn 2+ , respectively. The energy transfer from Ce 3+ to Mn 2+ was investigated and demonstrated to be a resonance-type via a dipole-dipole mechanism with the critical distance of about 4.1 A. The photoluminescence intensity ratio of blue and orange emission could be tuned by adjusting the concentration of Ce 3+ and Mn 2+ . The potential applications of these dual-emitting phosphors are the alternative blue and orange-emitting light emitting diode (LED) conversion phosphors due to their strong excitation bands in the wavelength range of 325-375 nm.