Dy³⁺and Tb³⁺ Doped SrSi₂O₂N₂ Polychromatic Phosphor And LED Device Packaging

Because of its advantages of environmental protection,long life,energy saving and high luminous efficiency,white LED is regarded as the most valuable lighting source of new green lighting in the 21st century.In order to solve the defects such as poor color rendering index(Ra<80)and high color temperature(>7000K)caused by the combination of YAG:Ce³⁺yellow phosphor and blue LED chip,the combination of UV or near-UV LED chips and red,green,blue mixed phosphors has become the preparation method of a new generation of white LEDs.As phosphors of different light colors are mixed,the difference in the substrate of phosphors will lead to the phenomenon of self-absorption between phosphors.In addition,the difference in thermal stability of different phosphors can also easily cause the phenomenon of color drift of white LED.The research and development of phosphors with multi-light emission from a single substrate is the key to solve the problem.In this paper,the multi light emitting SrSi₂O₂N₂:xDy³⁺?SrSi₂O₂N₂:yTb³⁺and SrSi₂O₂N₂:0.06Dy³⁺,yTb³⁺phosphors with single substrate were synthesized by high temperature solid phase method combined with two-step synthesis method.The main contents are as follows:(1)SrSi₂O₂N₂:0.06Dy³⁺phosphors were prepared by one-step synthesis and two-step synthesis.The XRD results of the phosphors showed that the phase composition of SrSi₂O₂N₂:0.06Dy³⁺phosphor synthesized in one step contained unknown phase,SrSi₂O₂N₂:0.06Dy³⁺phosphor prepared in two-steps is the pure phase of SrSi₂O₂N₂.Comparing the emission spectra of SrSi₂O₂N₂:0.06 Dy³⁺phosphors prepared by one-step synthesis and two-step synthesis,the peak emission of the two-step phosphor was about 4 times higher than that of the one-step phosphor.The method of two-step synthesis is obviously better than that of one-step.Subsequently,a series of SrSi₂O₂N₂ phosphors were prepared by high temperature solid phase method combined with two-step synthesis.(2)As for SrSi₂O₂N₂:xDy³⁺series phosphors,XRD results showed that a small amount of Dy³⁺substituted Sr²⁺into the crystal lattice of the matrix did not change the crystal structure of SrSi₂O₂N₂.According to the spectral detection,the emission spectra of the sample excited by 345nm mainly have two main emission peaks of 478 nm and 571 nm,which correspond to blue light(⁴F_9-2?⁶H_15-2)and yellow light(⁴F_9-2?⁶H_13-2),respectively,which can achieve the purpose of multi-light emission of a single substrate.The concentration quenching mechanism of SrSi₂O₂N₂:xDy³⁺phosphors was electric dipole-electric dipole interaction.Compared with the initial luminescence intensity,the luminescence intensity of SrSi₂O₂N₂:0.06 Dy³⁺phosphor at 100?and 150?decreased by only 1.6%and 15%respectively.This material has good thermal stability.(3)As for SrSi₂O₂N₂:yTb³⁺and SrSi₂O₂N₂:0.06Dy³⁺,yTb³⁺series phosphors,the XRD results showed that a small amount of Tb³⁺or Tb³⁺/Dy³⁺substituted Sr²⁺into the crystal lattice of the matrix did not change the crystal structure of SrSi₂O₂N₂.Scanning electron microscopy showed that SrSi₂O₂N₂:Tb³⁺and SrSi₂O₂N₂:Dy³⁺,and that the particles of Tb³⁺and SrSi₂O₂N₂:Dy³⁺were similar in shape,and the particle size was also between 9-11nm.According to the spectral detection,the green light emitted by SrSi₂O₂N₂:yTb³⁺phosphors can be observed under the excitation of 376nm,and the main emission peak is located at 545nm.The emission intensity of Tb³⁺reaches the maximum when the molar fraction reaches 0.08.Other emission peaks are located at 416nm,438nm,490nm,589nm and 627nm respectively,which can achieve the purpose of multi-light emission of a single substrate.The emission peaks of SrSi₂O₂N_2:0.06Dy³⁺,yTb³⁺(y=0-0.08)phosphors excited at 345nm are located at 416nm,438nm,478nm,490nm,571nm,589nm,and 627nm,which can also achieve the purpose of multi-light emission of a single substrate.(4)As for SrSi₂O₂N₂:0.02Eu²⁺,xDy³⁺series phosphor,according to the spectral detection results,only 4f-5d transition of Eu²⁺appears in the emission spectrum,which is the green emission peak at 525nm.The emission peak intensity of phosphors at 525nm decreased with the increase of the doping concentration of Dy³⁺,and the average decay time of Eu²⁺decreased gradually.The phosphors have the characteristics of optical information storage.SrSi₂O₂N₂:0.02Eu²⁺,0.02Dy³⁺have the best information storage effect.Oxygen vacancies in SrSi₂O₂N₂ crystals and Dy³⁺can provide trap centers for SrSi₂O₂N₂:0.02Eu²⁺,xDy³⁺phosphors.The phosphors"remember"the pattern information through ultraviolet light and a mask,and the center of the trap captures electrons that are excited to the conduction band.After the UV excitation is turned off,the phosphors are thermally stimulated to release the electrons back into the conduction band and then migrate to the 5d energy level of the Eu²⁺ion.The electrons in the 5d energy level jump to the 4f energy level,emitting green light and displaying the pattern that the phosphors"remembered".