Study On Luminescence Properties Of Silicate Phosphors

The MAl₂Si₂O₈:0.02Eu²⁺?M=Ca,Sr,Ba?series phosphors were prepared at 1250°C in a carbon-reducing atmosphere using a high-temperature solid-state method.Their crystal structures and spectral characteristics were studied.The series of samples all belong to the typical Eu²⁺4f⁶5d¹-4f⁷(⁸S_7/2)broad excitation band and emission band,and their emission centers were located at 438nm?Ca?,422nm?Sr?and 371nm?excitation at 330nm wavelength?.Ba),blue light.The resulting luminescence intensity decreased as the ionic radius increased.At the same time,the difference of the crystal field strength leaded to the lower 5d energy level of MAl₂Si₂O₈:0.02Eu²⁺,which decreased with the increase of cation radius,resulting in blue shift.Afterglow properties and oxygen vacancies are related to the ability to trap the electrons in the activator that transition to the 5d orbital under UV excitation.The greater the difference in the potential energy between the alkali metal cation and Eu²⁺,the greater the attraction between Eu²⁺and the oxygen vacancy,the higher the stability of the defect,and the higher the difference in potential energy between the alkali metal ion and Eu²⁺.The order was Ca²⁺,Sr²⁺,and Ba²⁺.Among them,the CaAl₂Si₂O₈ series was mainly studied.The concentration of Eu²⁺doped CaAl₂Si₂O₈ phosphor was quenched when the doping concentration was 4%mol.The emission peaks obtained at the excitation of 369 nm had a broad band emission spectrum of 440 nm.With the increase of Eu²⁺doping concentration,there was a clear red shift at the emission wavelength.By analyzing the asymmetry of the emission spectrum and referring to the related literature,there were two different crystal environments for Eu²⁺in the crystal.The emission spectrum of Eu²⁺in the CaAl₂Si₂O₈matrix in the emission spectrum had two emission peaks at 437nm and 469nm,respectively.The thermal stability analysis of the phosphor showed that the thermal stability of the LED at a normal operating temperature of 150 degrees Celsius was only maintained at 65%of room temperature.By analyzing the spectrum of CaAl₂Si₂O₈:Ce³⁺,it can be found that there was a large overlap between the emission spectrum of the doped Ce³⁺and the excitation spectrum of the doped Eu²⁺.Therefore,we performed appropriate Ce³⁺co-doping on CaAl₂Si₂O₈:Eu²⁺.The experimental results show that with the increase of co-doped Ce³⁺concentration,the luminescence intensity first decreased,then increased and then decreased.The first reduction may be due to the fact that the energy transfer between Eu²⁺and Ce³⁺produces a cross-relaxation effect that in turn reduces the absorption of Eu²⁺.It may also be due to the unequal substitution of Ce³⁺to Ca²⁺that will cause positively charged Ce_Ca point defects in the crystal,and these additional defects will store a portion of the excitation energy,resulting in lower emission intensity.As the Ce³⁺concentration continues to increase,it is observed that the luminescence intensity gradually increases.By calcining CaAl₂Si₂O₈:Eu in air and vacuum respectively,the existence of Eu²⁺in CaAl₂Si₂O₈ self-reduction phenomenon and the conclusion that aluminum oxide tetrahedron and silica tetrahedron cannot completely shield oxygen are proved.Phosphor by adding excess SiO₂ of CaAl₂Si₂O₈:0.02Eu x SiO₂?x=0,0.05,0.100,0.200,0.300?.With the addition of excess SiO₂,the emission intensity of Eu²⁺would gradually decrease,and the emission intensity of Eu³⁺would gradually increase.Charge compensation model based on self-reduction phenomenon,the self-reduction phenomenon can be controlled by doping charge compensators,hole compensators,and silica.