Synthesis And Luminescent Properties Of Highly Efficient And Thermally Stable(Fluoro) Phosphate Phosphors

White light-emitting diode?WLEDs?is a widely used solid-state lighting source in recent years,which has advantages such as energy saving and environmental friendliness,etc.Among the many synthetic methods of WLEDs,phosphor-converted White Light light-emitting Diode?pc-WLEDs?is one of the most common methods to realize WLEDs.The widely used commercial pc-WLED is the combination of a blue LED chip and Y₃Al₅O₁₂:Ce³⁺(YAG:Ce³⁺)phosphor.However,this kind of w-LED has a low color rendering index?CRI?and a high correlated color temperature?CCT?due to the lack of red light component.There are several strategies to surmount the above drawback,such as adding a red phosphor into the‘‘blue chip+YAG:Ce3+''system,combining a blue chip with a green and a red phosphor,coating a near-UV LED with blue,green,and red phosphors,or combining a near-UV chip with a white-emitting phosphor.The last form can not only achieve white light with a high CRI,but also avoid reabsorption between phosphors.No matter which method is used,phosphors with high quantum efficiency and good thermal stability are needed to improve the performance of LED devices.Based on this goal,this paper take K₂Ca?PO₄?F:Eu²⁺and KSrBaPO₄:Eu²⁺as the research objects,to study single-doped white phosphor.Take KSrBaPO₄:Eu²⁺as the research object,the solid-solution is used to adjust the spectrum,and the phosphor with high quantum efficiency and thermal stability is obtained.The main findings are as follows.1.K₂Ca?PO₄?F:Eu²⁺phosphor was synthesized by high-temperature solid-state reaction method.The color-tunable phosphor exhibits two broad emission bands peaking at 485 and 660 nm upon UV excitation.White emission is realized in K₂Ca?PO₄?F:0.006Eu²⁺.The internal and external quantum efficiencies of the white-emitting phosphor are 91.5 and66.9%,respectively.The phosphor also exhibits good thermal stability,namely,the emission intensity at 423 K maintains 80%of that at room temperature,and the intensity ratio between the two emission bands remains nearly unchanged within 423 K.A white LED device has also been fabricated by using a 365 nm LED chip and K₂Ca?PO₄?F:0.006Eu²⁺,showing a high color rendering index?R_a=87.6?.These results indicate that the K₂Ca?PO₄?F:Eu²⁺phosphor is a promising candidate for UV-pumped w-LEDs.2.Phosphors KSr_0.99-xBa_xPO₄:0.01Eu²⁺?x=0-0.99?were synthesized by high-temperature solid-state reaction method.Phase analysis and structural refinement indicate that complete solid solution is realized.The emission band shifts from 425 to 420 nm slightly with the increase of Ba content,however,with obviously different emission intensity.The emission intensities of the phosphors at 150°C are all higher than 90%of the room-temperature value,indicating good thermal stability.KSr_0.99PO₄:0.01Eu²⁺exhibits the best thermal stability among them within 150°C,while it is KBa_0.99PO₄:0.01Eu²⁺at temperature higher than150°C.Activation energy and structural rigidity are responsible for the thermal stability at lower and higher temperature,respectively.The internal quantum efficiencies of the samples are all higher than 85%,among which KBa_0.99PO₄:0.01Eu²⁺reaches up to 96.2%.Combined with the largest absorbance of the excitation source,KBa_0.99PO₄:0.01Eu²⁺exhibits the strongest blue emission.Furthermore,a warm white pc-LED was fabricated based on the as-synthesized KBa_0.99PO₄:0.01Eu²⁺and other commercial phosphors,which has a high color rendering index?92.1?.These results indicate that the solid-solution method is feasible to explore color-tunable,highly efficient and thermally stable phosphors for solid-state lighting.