Preparation And Luminescence Properties Investigation Of Several Novel Phosphate Phosphors Activated By Eu²⁺/Eu²⁺-Mn²⁺ Ions

Recently,high power phosphor convert light emitting diodes?pc-LEDs?have been regarded as a new generation of lighting source for solid state lighting following incandescent and energy saving lamps due to their unique advantages,such as high efficiency,energy-saving,compactness and environmentally friendly.To achieve optimal luminous efficiency,maximal color gamut and stable color reproducibility,it is essential to find high-efficiency phosphors with narrow bands and strong thermal stability.At present,among the many implementation schemes of pc-LED,the“near-ultraviolet?n-UV?LED chip+three primary colors?red,blue,and green?/single host color-adjustable phosphor”solution is considered as the most potential candidate.However,there is a shortage of highly efficient blue or single-host adjustable-color phosphor that can be directly used in the above scheme,so it is necessary to investigate and develop novel blue emitting phosphors and investigate their luminescence property.As an important family of inorganic materials,phosphate compounds have attracted the attention of academia and industry due to their high ionic conductivity,low thermal expansion and high chemical stability.In this work,novel blue emitting phosphors Na3XMg7?PO4?6:Eu²⁺?X=K,Rb,Cs?and color-adjustable Na3XMg7?PO4?6:Eu²⁺,Mn²⁺?X=K,Rb,Cs?phosphors are prepared by traditional high temperature solid state reaction method.The crystal structure,phase purity,luminescence characteristics,thermal stability and energy transfer mechanism of these phosphors are studied.The details are as follows:?1?A novel magnesium phosphate phosphor Na3RbMg7?PO4?6:xEu²⁺(NRMP:xEu²⁺),which has efficient blue emission and excellent thermal stability has been synthesized firstly through high temperature solid state reaction method.The local structure of Eu²⁺are confirmed through XRD Rietveld structral refinement,steady and transient time-resolved spectra.The photoluminescence properties of NRMP:Eu²⁺phosphor has been optimized by varying the doping concentration of Eu²⁺ions,as well as the mechanism of concentration quenching has been studied in detail.Furthermore,they possess a rather high thermal quenching temperature.When the environment temperature reaches to 140?,the emission intensity still maintains 96%of its initial intensity.Besides,the white LED lamp with high color rendering index?Ra=85.81?and an appropriate correlated color temperature?CCT=4468 K?is fabricated.Finally,through co-doping Eu²⁺-Mn²⁺,the energy transfer and related mechanism are clarified the tunable color from blue to red is realized..All the results indicate that NRMP:Eu²⁺/Eu²⁺,Mn²⁺phosphors can act as an excellent phosphor for pc-LEDs.?2?Na₃KMg₇?PO₄?₆:xEu²⁺(NKMP:xEu²⁺)with blue emission and NKMP:xEu²⁺,zMn²⁺phosphor with adjustable color are prepared for the first time through the traditional high temperature solid state reaction method.Under near-ultraviolet excitation,the optimized NKMP:Eu²⁺phosphor produces a bright blue emission peak at 447 nm.The emission intensity gradually increases with the increase of Eu²⁺concentration,and the concentration quchching appears at x=0.01.Then,the emission intensity is gradually decreased with the increase of Eu²⁺concentration.The thermal stability of NKMP:Eu²⁺phosphors is confirmed by measuring its thermal quenching spectra.The results show that the emission intensity decreases monotonically with increasing temperature and keeps at82%of the initial value under 140°C.Finally,NKMP:Eu²⁺,Mn²⁺phosphors with adjustable color in the visible range are prepared.In the emission spectrum of this phosphor,as the Mn²⁺concentration increases,the emission intensity of Eu²⁺decreases monotonically,while the emission intensity of Mn²⁺increases first and then decreases,and the strongest emission occurs at y=0.04.This phenomenon fully indicates that there exists an energy transfer process between Eu²⁺-Mn²⁺in the phosphor.Futhermore,by changing the concentration ratio of Eu²⁺-Mn²⁺,an adjustable emissionspectrum can be achieved from blue light to red light.?3?Na₃CsMg₇?PO₄?₆:x Eu²⁺(NKMP:xEu²⁺)with blue emission and NKMP:xEu²⁺,yMn²⁺phosphors with adjustable color are prepared by traditional high-temperature solid state reaction method.It can be obtained from XRD analysis that doping does not introduce impurity phases.The phosphor can be effectively excited by UV and n-UV light,which can match well with the current commercial LED chips.When 400 nm near-ultraviolet light is used as the excitation source,the sample emits blue light ranging from 400 to 600 nm with dominated emission at 461 nm,which corresponds to the 4f⁶5d¹⁴f⁷ transition emission of Eu²⁺.The emission intensity increases first and then decreases with the increase of Eu²⁺concentration,and the emission intensity reaches the largest value at x=0.02.And then,under 400 nm excitation,the internal quantum efficiency?IQE?of the NCMP:Eu²⁺blue phosphor can reach 93%,which is equivalent to the commercial blue phosphor BaMgAl₁₀O₁₇:Eu²⁺(BAM:Eu²⁺).In addition,the phosphor has stable thermal quenching performance,the emission intensity still maintains 82%of the original intensity at 140?.Finally,by co-doping with Eu²⁺and Mn²⁺,it is found that the adjustment from the blue light to the red light can be achieved by modifying the Eu²⁺-Mn²⁺concentration ratio.In summary,NKMP:Eu²⁺and NKMP:Eu²⁺,Mn²⁺phosphors have great potential in the application of high-power LED devices.