Preparation Of Novel Phosphate Phosphors By Chemical Unit Substitution

The combination of chip and phosphor is the primary way to achieve white LEDs.Good luminescence and thermal stability are essential to the practical application of phosphors.Therefore,in recent years,many efforts have been made in the design and discovery of new phosphors for solid-state lighting,many new strategies have been proposed.Chemical unit cosubstitution strategy is one of the important strategies.Structural modifications on the existed compounds by substitution can tune and optimize the photoluminescence and improve other properties.In this paper,three known phosphors Sr4.95?PO4?3F: 0.05Eu²⁺,Ca1.98?BO3?Cl: 0.02Eu²⁺,Ba2.97?PO4?2: 0.03Eu²⁺ are as beginning member.By utilizing the chemical unit cosubstitution strategy,the existed chemical composition is changed,the coordination environment of activation is also changed so that the luminescence and other properties of original phosphors are changed.The first chapter mainly introduces the development history,the application status,the existing problems and the development prospects of LEDs and phosphors,which provides a experimental idea and theoretical basis for the thesis research topic.The second chapter of the paper mainly introduces the preparation of samples and the related raw materials and instruments used in preparation and characterization.The third chapter of the paper synthesized a series of Sr4.95?PO4?3X: 0.05Eu²⁺?X = F,Cl,Br?phosphors by high temperature solid-state method,we could see that all the samples were pure phase by XRD.This chapter studied the emission spectra and thermal stability of phosphors after substitution by halogen ions,and further studied the reasons for the change of thermal stability of phosphors in detail.By compared this series of phosphors,we could know that the luminescent properties and thermal stability of Sr4.95?PO4?3Br: 0.05Eu²⁺ phosphors were very good relatively,so we continued to study the crystal structure and luminescent propertier of Sr5?1-x??PO4?3Br: 5x Eu²⁺ phosphor,the optimal doping concentration of Eu²⁺ ions was 2.0mol%,the quenching mechanism of concentration could be expressed by Quadrupol-quadrupole interactions.All the data showed that Sr5?1-x??PO4?3Br: 5x Eu²⁺ phosphor has good thermal stability,high color purity and color stability,these results reveal that Sr5?PO4?3Br: Eu²⁺ blue phosphor has great potential in the application of white LED.In the fourth chapter,a series of Ca1.98?BO3?1-x?PO4?xCl: 0.02Eu²⁺?x= 0,0.05,0.10,0.15,0.20,1?phosphors were prepared by high temperature solid-state method at 850?.Through the chemical unit replacement strategy,replacing the [BO3]3-anion polyhedron with [PO4]3-anion polyhedron and changing the crystal field environment around Eu²⁺,There are 4 Ca sites in the compound so that the luminescent color of the phosphor changed.Based on thus property,the light color were realized from yellow to warm white and finally to blue successfully by changing the substitution amount.When x=0.10,we achieved single matrix white emission of Ca1.98?BO3?0.9?PO4?0.1Cl: 0.02Eu²⁺,it was only necessary to dope Eu²⁺ alone to avoid the energy loss between the various activated ions.In addition,we also investigated the thermal stability of the phosphor after substitution and explained the diversification of thermal stability by calculating Ea.The results showed that the Ca1.98?BO3?1-x?PO4?xCl: 0.02Eu²⁺?x= 0,0.05,0.10,0.15,0.20,1?phosphor had potential applications in white LEDs.The fifth chapter also synthesized two series of phosphors: Ba3-2xLaxNax?PO4?2: Eu²⁺/Eu³⁺ and Ba3-2xYxLix?PO4?2: Eu²⁺/Eu³⁺ by high temperature solid-state method at 900?.replacing [Ba²⁺,Ba²⁺] ion pairs in Ba2.97?PO4?2: 0.03Eu²⁺ with [La³⁺,Na+] and [Y³⁺,Li+] ion pairs by chemical unit substitution strategy provided sites for Eu³⁺ so that Eu²⁺ and Eu³⁺ coexist.By adjusting the amount of substitution to adjust the Eu²⁺/Eu³⁺ ratio in phosphors,meanwhile,the spectral regulation could be achieved.The light color in the Ba3-2xLaxNax?PO4?2: Eu²⁺/Eu³⁺ phosphors realized the change from blue-purple to red,and it wasn't possible to pass through the white area.In the Ba3-2xYxLix?PO4?2: Eu²⁺/Eu³⁺ system,the luminescence color of the phosphor changes from blue-violet to white and red.At the same time,we also studied the trend of changes in the thermal stability of phosphors after replaced.The results shown that the thermal stability of the sample after substitution is slightly better than before the substitution.