| As a new type of light source in the 21 st century, white light-emitting diodes have many advantages such as environmental protection and energy saving, long lifetime, high energy efficiency when compared with traditional incandescent lamp and fluorescent lamp.The current mainstream approach to make LEDs is combing an ultraviolet/near-ultraviolet(n-UV) emitting LED with tricolor(blue, green, and red) emitting phosphors. Therefore, it is a significant task to explore a novel phosphor which can be efficiently excited by ultraviolet/near-ultraviolet LED chips. In this paper, some new phosphors excited by UV for w-LED have been synthesized via a solid-state reaction and the photoluminescence(PL)properties, thermal stability properties and quenching concentration mechanism were investigated in detail.(1) Novel Na3YSi2O7:Sm3+phosphors for white light-emitting diodes(w-LEDs)were prepared by a conventional high-temperature solid-state reaction. X-ray diffraction,photoluminescence spectra and temperature-dependent emission spectra were utilized to characterize the structure and luminescence properties of the synthesized phosphor. The phosphor can be efficiently excited by the near-UV light, and emit red-orange light. The emission spectra contain exclusively the characteristic emission of Sm3+, namely,4G5/2â†'6H5/2(564 nm)4G5/2â†'6H7/2(583 nm)4G5/2â†'6H7/2(609 nm) and4G5/2â†'6H9/2(651nm). It was found that the critical quenching concentration of Sm3+ in the Na3YSi2O7 host is about 3 mol % and concentration quenching is ascribed to dipole-dipole interaction. The chromaticity coordinates(x, y) of Na3YSi2O7:0.03Sm3+phosphor are calculated to be(0.5449, 0.4472). The activation energy for thermal quenching is deemed to be 0.22 e V.The research suggests that Na3YSi2O7: Sm3+ is a potential candidate for application in w-LEDs.(2)A series of Sr3 Gd Na(PO4)3F: Sm3+ phosphors for white light-emitting diodes(w-LEDs) were synthesized through high-temperature solid-state reaction. The photoluminescence excitation and emission spectra, temperature-dependent emission spectra and decay time were investigated in detail. The excitation and emission spectra indicate that these phosphors can be efficiently excited in the range from 350 to 430 nm which matches perfectly with the near-UV light, and emit orange-red light with CIE coordinates(0.5811, 0.4181). The concentration quenching mechanism of Sm3+ ions was ascribed to the dipole-dipole interaction. The activation energy E for thermal quenching is calculated to 0.242 e V. And the lifetime of the Sr3Gd(1-x)Smx Na(PO4)3F(x = 0.03, 0.05,0.07, 0.09) phosphor were determined to be 0.8669 ms, 0.8643 ms, 0.8525 ms, 0.8232 ms respectively.(3)A series of Sr3Gd(1-x)Dyx Na(PO4)3F(SGNP: x Dy3+, x = 0.01, 0.03, 0.05, 0.07,0.09) phosphors for white light-emitting diodes(w-LEDs) were synthesized by a conventional solid-state reaction method. The X-ray diffraction results confirm that the as-prepared samples are pure phase. The phosphor gives two intense emission bands centering at 481 nm and 574 nm which can be attributed to the 4F9/2 â†' 6H15/2 transition and the4F9/2 â†'6H13/2 transition, respectively. The chromaticity coordinates(x, y) of this phosphor are calculated to be(0.3054, 0.3354) which locate on the region of white light region under the excitation at 350 nm. The concentration quenching mechanism of Dy3+ions was ascribed to the dipole-dipole interaction. These results indicate that phosphors may be potential application in the w-LEDs. |
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