| Semiconductor lighting and LCD backlight display technology based on white light-emitting diodes(LEDs)have covered all fields of society and are closely linked to people’s production and life.In recent years,people’s demand for the quality of white LED light sources and related devices has been continuously improving,and the depth and breadth of basic research in the field of LED application related materials and devices have been promoted.In the field of LED lighting,full-spectrum lighting is the current research hotspot,hence cyan phosphors and single-phased white phosphors attract much attention;in the field of LED backlight display,it is urgent to develop narrow-band green phosphors to meet the needs of wide color gamut display.Based on different LED application orientations,this research is devoted to the exploration of high-performance rare earth phosphors with different luminescent characteristics by using UCr4C4 as the structural prototype,which can be divided into the following aspects:(1)A UCr4C4-type narrow-band cyan-emitting phosphor NaK(Li3SiO4)2:Eu2+was designed and synthesized,which can be excited by the blue LED chips and shows cyan emission at 486 nm with a narrow full width at half maximum(FWHM)of 20.7 nm.The narrow-band cyan emission results from the highly condensed and rigid structure and the high-symmetry cation sites.This phosphor allows the valley between the blue and yellow emission peaks in the white LED device to be filled,and the color-rendering index can be enhanced from 86 to 95.2,which is closed to full-spectrum lighting.Furthermore,the fine-tuning of the narrow-band cyan phosphors,MNa2K(Li3SiO4)4:Eu2+(M=Rb,Cs)was realized by cation substitution strategy.The emission peak assignments were elaborated,and the variations of luminescence properties and thermal quenching behavior with compositional changes of alkali cations were discussed in detail.(2)A UCr4C4-type narrow-band green-emitting phosphor,RbLi(Li3SiO4)2:Eu2+,with excellent luminescence thermal stability was designed and synthesized.RbLi(Li3SiO4)2:Eu2+ phosphor can be efficiently excited by blue light and shows green emission at 530 nm with an FWHM of 42 nm,which is better than the commercial narrow-band green phosphor β-SiAlON.The white LED backlight using RbLi(Li3SiO4)2:Eu2+ phosphor as the green component demonstrates a high luminous efficacy of 97.28 lm W-1 and a wide color gamut(107%NTSC).In order to improve the stability of RbLi(Li3SiO4)2:Eu2+,we proposed a surface treatment scheme by combining the atomic layer deposition of Al2O3 and hydrophobic modification by octadecyltrimethoxysilane to construct the dual-shelled protective layer,which can remarkably improve the moisture resistance of RbLi(Li3SiO4)2:Eu2+.(3)UCr4C4-type single-phased white NaLi3Si1-xO4:Eu2+(0.15≤x≤0.25)phosphors were designed and synthesized.Stochiometric NaLi3SiO4:Eu2+exhibits narrow-band blue emission at 469 nm(FWHM=33 nm),while the samples with Si content reduced by 15-25%display white emission with two peaks at 472 nm(FWHM=40.5 nm)and 585 nm(FWHM=162 nm).The narrow-band blue peak is ascribed to the 5d→4f transition of Eu2+at highly symmetric cuboid Na sites,while the broad-band yellow emission arises from the defect-induced charge-transfer emission,which has a large Stokes shift and long decay time.A single-component white LED device with a color-rendering index(Ra)of 82.9 can be fabricated by employing the white phosphor. |
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