Luminescence And Energytrasfer Investigation On The Different Rare-Earth Ions Doped Sr₉Mg_1.5(PO₄)₇ Phosphors With White Whitlockite ?-Ca₃(PO₄)₂ Type

Considering to the continuous-increasing energy crisis problems and environmental concerns,there is an urgent need to develop a high-efficiency light source to reduce the energy consumption.Regarded as the fourth generation,white light-emitting diodes(WLEDs)are attracting much attention to researchers because of the inimitable advantages,such as environment friendly,long service life and energy conservation.Until now,a lot of optical materials with combinations of trivalent rare-earth ions and phosphates have been investigated.On one hand,phosphate is common to be found in most mineral with outstangding physical and chemical stability,excellent optical performance and simple synthesis method.On the other hand trivalent rare-earth ions can exhibit various emission colors covering blue to red regions when pumped by near-ultraviolet radiation.According to the report of phosphate phosphors doped with trivalent rare-earth ions,the red phosphors suffer from low color purity,tough preparation method.Meanwhile,the lack of single matrix white phosphors is influence the development of the WLED.In order to solve the problems,it is an urgent need to develop novel red phosphors and single matrix white light phosphors.So in this article,a series of novel red phosphors Sr₉Mg_1.5(PO₄)₇:Sm³⁺,R⁺(R⁺=Li,Na,K)and single matrix white light phosphors Sr9Mg1.5(PO4)7:0.01Tm³⁺,y Dy³⁺(0.02?y?0.20)phosphors were synthesized by high temperature solid-state method.Meanwhile,the photoluminescence spectra,crystal structure,phase purity,decay times,energy transfer and luminescence spectra as a function of tempreture were measured and investigated in detail.A series of novel red phosphors Sr₉Mg_1.5(PO₄)₇:Sm³⁺,R⁺(R⁺=Li,Na,K)were synthesized by high temperature sintering method with the activator of Sm³⁺and the charge compensator of R⁺(R⁺=Li,Na,K).The coordination environment of Sr²⁺ions in the matrix lattice was reconfirmed according to the Rietveld structure refinement patterns.The Sr₉Mg_1.5(PO₄)₇:x Sm³⁺(0.02?x?0.30)phosphors exhibit strong red emission at 598nm and 650 nm,which is attributed to the ⁴G_5/2-⁶H_7/2 and ⁴G_5/2-⁶H_9/2 transitions of Sm³⁺ions.The CIE coordinate of Sr9Mg1.5(PO4)7:0.2Sm³⁺is(0.6066,0.3923),and the color purity can reach 98.8%.In addition,in order to improve the emission intensity and thermal stability of the sample,Li⁺,Na⁺and K⁺charge compensators were introduced into the Sr₉Mg_1.5(PO₄)₇:0.2Sm³⁺sample.The optimized Sr₉Mg_1.5(PO₄)₇:0.2Sm³⁺,0.2Na⁺sample can exhibit stronger emission intensity which has potential applications in solid-state lighting field.A series of Sr₉Mg_1.5(PO₄)₇:0.01Tm³⁺,y Dy³⁺(0.02?y?0.20)phosphors were prepared by conventional sintering method.All the prepared phosphors crystalized to single phase.When excited by 358 nm,the emission hue of Sr₉Mg_1.5(PO₄)₇:0.01Tm³⁺,y Dy³⁺(0.02?y?0.20)turned from blue to white by modifying the Tm³⁺/Dy³⁺ratio.In addition,we also discussed the energy transfer from Dy³⁺to Tm³⁺ions phenomenon and the overlap PL/PLE spectra,emission strength increasing and decreased lifetime indicated energy transfer from Dy³⁺to Tm³⁺ions with 53.05%energy transfer efficiency.Furthermore,the CIE chromaticity coordinates of Sr₉Mg_1.5(PO₄)₇:0.01Tm³⁺,0.20Dy³⁺located at(0.3279,0.3299)which is closed to standard white CIE chromaticity coordinates(0.33,0.33).The emission intensity can remain 95%at 150°C compared with the original emission intensity at ambient temperature.All the results indicate the potential application in single phased white LED.