Effect Of Ion Doping/substitution On Crystal Phase Transition And Luminescence Properties Of Ba₃P₄O₁₃:Eu²⁺ Phosphors

Solid-state white LEDs have many outstanding advantages as a new type of lighting source.Compared with traditional lighting methods,white LEDs have attracted much attention due to their excellent energy efficiency and long service life.At present,the main way to realize white light is the combination of LED chip with phosphors.In order to solve the problem of low color rendering index and high correlated color temperature in this combination,many studies mainly focus on developing comprehensive strategies for new phosphor materials and optimization of their optical properties.As a new means of structure designing and performance regulating,crystal phase engineering strategy is continuously applied in the research of new functional materials.The luminescence properties can be regulated and optimized by introducing a portion of the foreign ions into the known substance to cause a transition between different crystal phases in the same host.In this paper,partial substitution of various ions(Ca²⁺/Mg²⁺/Gd³⁺/Y³⁺/Sr²⁺/Zn²⁺)is carried out in the known Ba₃P₄O₁₃:Eu²⁺phosphor,which realizes the mutual transformation between LT-Ba₃P₄O₁₃ and HT-Ba₃P₄O₁₃,and the law of crystal phase transitions and luminescent properties caused by different types of substituted ions were further explored.In the first chapter,the white LED is briefly introduced,and the main ways to realize white light,the composition of phosphor and the principle of luminescence,the design strategy of new single-host white phosphor and the idea of photoluminescence tuning application of crystal phase engineering,etc are introduced.The second chapter mainly introduces the synthesis conditions and processes of phosphors and the instrument information used for the structural and performance characterization of phosphors.In the third chapter,Ba_3?0.997-x?P₄O₁₃:0.009Eu²⁺,3xCa²⁺?x=0.00-0.04?and Ba_3?0.997-x?P₄O₁₃:0.009Eu²⁺,3xMg²⁺?x=0.00-0.12?phosphors with different Ca²⁺/Mg²⁺concentrations were synthesized by high temperature solid-state method at850°C.According to XRD analysis,only at the temperature lower than the phase transition and the formation of the high temperature phase,The substitution of Ca²⁺/Mg²⁺causes the phosphors to undergo a transition from a low temperature phase to a high temperature phase.The luminescence of Eu²⁺also moves from the blue light emission of the main peak at 450 nm to the yellow-green light emission with a main peak of about 530 nm/550 nm.The CIE color coordinates move from blue to cyan-white and finally to yellow-green.By comparing the thermal stability of the low temperature phase and the high temperature phase,the low temperature phase has good thermal stability,the calculated activation energies were E_a1=0.309 and E_a2=0.264respectively.In the fourth chapter,Ba_2.991-1.5xP₄O₁₃:0.009Eu²⁺,xGd³⁺?x=0.00-0.08?/Ba_2.991-1.5xP₄O₁₃:0.009Eu²⁺,xY³⁺?x=0.00-0.08?phosphors were synthesized by the traditional high temperature solid-state method at 850°C,the crystal phase transition from the low temperature phase to the high temperature phase was successfully achieved by changing the concentration of Gd³⁺/Y³⁺substituting Ba²⁺.The Gd³⁺/Y³⁺substitution driver the main peak of the emission spectrum of the phosphor move from450 nm to 550 nm.The CIE of phosphors also move from blue to white finally to yellow light region,realizing the white light emission in a single host,which further proves that the crystal phase transformation is an effective way for Photoluminescence tuning.Partial substitution of Gd³⁺/Y³⁺can increase the excitation peak intensity of LT-Ba₃P₄O₁₃:Eu²⁺blue phosphor by 59%and 15%,respectively.The fifth chapter introduces a series of Ba_3?0.997-x?P₄O₁₃:0.009Eu²⁺,3xSr²⁺?x=0.00-0.25?phosphors synthesized by the traditional high temperature solid-state method at 900°C.XRD powder diffraction analysis showed that a small amount of Sr²⁺substituted Ba²⁺caused the crystal phase transition of the high temperature phase to the low temperature phase of the phosphor at the temperature at which the high temperature phase was formed.Sr²⁺replaced two different Ba sites in Ba₃P₄O₁₃:Ba1?CN=7?,Ba2?CN=8?.The substitution of Sr²⁺drivers the main peak of the emission spectrum of the phosphor from the yellow light emission at 550 nm to the blue light emission at 450 nm instantaneously,As the substitution concentration of Sr²⁺further increases,the emission peak gradually blue shift,which proves that Sr²⁺substitution causes redistribution of Eu²⁺in different Ba²⁺sites.Eu²⁺occupies Ba1 site with a long Ba-O bond length resulting in a weaker crystal field and the blue shift of the spectrum.The CIE color coordinates of the phosphor change from yellow to blue then move toward the dark blue region with the increasing concentration of Sr²⁺.This series of changes proves that the crystal phase transition strategy caused by foreign ions has important application prospects in the photoluminescence tuning of phosphors.In the sixth chapter,a series of Ba_3?0.997-x?P₄O₁₃:0.009Eu²⁺,3xZn²⁺?x=0.00-0.08?phosphors were synthesized at 850°C.It was found by phase analysis that the substitution of Zn²⁺did not cause phase transition in the host.The structural disorder of the samples were incresed,and gradually tends to an amorphous state.Emission spectra of different phosphors are always maintained in blue light emission without significant shifting.