Structural Design And Properties Of Eu²⁺ Activated Phosphate-based Luminescent Materials

Nowadays,problems such as the deterioration of the global ecological environment and energy shortage need to be solved urgently.Low-carbon,environmentally friendly and sustainable development has become an important development goal of all countries.Semiconductor lighting based on light emitting diode(LED)has become an industry highly in line with the theme of the times due to its advantage of energy-saving and environmental protection.Now the development of LED lighting industry has become the focus of our government.In order to promote the development of white LED,the research and development of new phosphor materials is particularly important.In this paper,Eu²⁺doped phosphors were prepared by traditional high temperature solid-state reaction method.Aiming to obtain the high-quality white light LEDs,new phosphor materials that can meet different applications were obtained by spectral regulation methods such as energy transfer,structural site engineering strategy and so on.The main research results are as follows:1.Red,green and blue phosphors were prepared by doping Eu²⁺,Tb³⁺and Mn²⁺ions in Na₄Ca₄Mg₂₁(PO₄)₁₈(NCMP).The crystal structure,phase,site occupancy and luminescence properties of NCMP:Eu²⁺,Tb³⁺,Mn²⁺were studied in detail.Under the335 nm excitation,the NCMP:Eu²⁺phosphors exhibited blue emission with peak at 422nm.Due to reabsorption and energy transfer,the spectra of NCMP:Eu²⁺phosphors shown an obvious red shift with the increase of doped Eu²⁺concentration.By combining luminescence spectra and decay curves,the efficient energy transfer(ET)processes of Eu²⁺?Tb³⁺and Eu²⁺?Mn²⁺were analyzed.And the ET efficiency of NCMP:0.01Eu²⁺,y Tb³⁺is 92.58%at y=0.15,while that of 99.85%for NCMP:0.01Eu²⁺,z Mn²⁺phosphors at z=0.15.By tuning the relative ratio of Eu²⁺/Tb³⁺/Mn²⁺,the bright blue,green,red or even warm white phosphors can be obtained.The emission intensity,quantum efficiency and thermal stability of these phosphors were improved due to the efficient energy transfer processes.In addition,the white LED lamps prepared by combining the 385 nm chip and our phosphors exhibit excellent performance.These results proved that the NCMP:0.01Eu²⁺,y Tb³⁺and NCMP:0.01Eu²⁺,z Mn²⁺materials can be used in white LEDs as potential green and red phosphors.2.Cyan green emitting phosphors were prepared by doping Eu²⁺in K₃Sc(PO₄)₂.By adjusting the doping Eu²⁺concentration,the spectral redshift from 468 nm to 497nm of the K₃Sc(PO₄):Eu²⁺phosphors can observed due to the variation of the crystal field.The integrated intensity of K₃Sc(PO₄)₂:0.05Eu²⁺can still remain 90.02%of initial intensity at 423 K.Under pressure,the emission spectra of the K₃Sc(PO₄)₂:Eu²⁺shown continuous red shift with shift rate of 7.9 cm^-1/kbar,indicating that the phosphor has a good application prospect in optical pressure sensor.In the compression and decompression process at 0 GPa,the profile and position of the normalized PL spectra of the K₃Sc(PO₄)₂ are consistent,proving the excellent structural rigidity and stability.WLEDs devices shown high color rendering index(R_a)with 87.5 and low correlated color temperature(CCT)with 4505 K.The results shown that the broad cyan-green emitting phosphor can be used not only in WLEDs for closing the cyan cavity,but also in the field of optical pressure sensor.3.The full spectrum white emitting phosphors Ca₉Na_1-xLi_xSc_0.667(PO₄)₇:Eu²⁺were synthesized by traditional solid-state reaction technology.The Ca₉Na Sc_0.667(PO₄)₇:Eu²⁺sample is a broad cold white light emitting phosphor with the emission centers at about480 and 610 nm.By introducing the Li⁺ions in Ca₉Na Sc_0.667(PO₄)₇:Eu²⁺phosphor,the Eu²⁺ions gradually show the optimum distribution in the Ca1,Ca2/Ca3 and Na sites.The induced effect of Li⁺ions improve the luminous intensity,increase the red component and change the emission color from cold white via warm white to orange.A special charge compensation mechanism is proposed to explain the enhancement of luminescence performance.A warm light WLED device was produced by coating the white emitting Ca₉Na_0.8Li_0.2Sc_0.667(PO₄)₇:2%Eu²⁺phosphors on 385 nm LED chip,which shown high R_a of 92.9,low CCT of 4529 K and excellent color stability under working temperature.The result indicates that the Ca₉Na_0.8Li_0.2Sc_0.667(PO₄)₇:2%Eu²⁺warm white emitting phosphors have potential applications in full-spectrum solid state lighting.4.A series of multifunction full spectrum white emitting phosphors Ca₉Na Zn_1-yMg_y(PO₄)₇:Eu²⁺were prepared by solid-state method.Since Eu²⁺ions enter the Ca3,Ca1/Ca2,and Na sites,the bright yellow emitting phosphor Ca₉Na Zn(PO₄)₇:1.0%Eu²⁺show three emission peaks at about 415,490,and 570 nm,respectively.By introducing Mg²⁺ions into Ca₉Na Zn(PO₄)₇:1.0%Eu²⁺phosphor,the redistribution of Eu²⁺in the Ca3,Ca1/Ca2,and Na sites is realized;the occupation of Eu²⁺in Ca3 site(415 nm)is decreased;and finally the harm of blue light to human health is reduced.Meanwhile,the emission center of Eu²⁺ions at Na sites show an obvious red shift from 562 to 634nm,and the emission color change from yellow to warm white with increasing the red component.The R_a of WLED devices manufactured by combining the Ca₉Na Zn_1-yMg_y(PO₄)₇:1.0%Eu²⁺(y=0 and 0.6)phosphors with 375 nm chip promotes from 79.9to 90.3,demonstrating that the Ca₉Na Zn_1-yMg_y(PO₄)₇:1.0%Eu²⁺can as a full spectrum white emitting phosphor using in full-visible-spectrum lighting.The maximum relative sensitivity S_r of Ca₉Na Zn(PO₄)₇:1.0%Eu²⁺is fitted to be 0.81%K^-1 at 398 K,demonstrating the potential applications of the phosphors in optical thermometry.In addition,the emission redshift rate(d?/d P)of Ca₉Na Zn(PO₄)₇:1.0%Eu²⁺phosphor under pressure is?5.21 nm/GPa,confirming that the phosphors are suitable for optical pressure sensing.