Performance Analysis Of Several Zn Long Afterglow Luminescent Materials Based On Defect Luminescence And Exploration Of Luminescence Mechanism

The long afterglow luminescent materials were systematically investigated and their latest researches and development trends were reviewed in this dissertation.Three kinds of materials with wide band gap energy,good thermal stability and chemical stability,ZnAl₂O₄,Zn₂SiO₄ and SrZn₂?PO₄?₂ were explored as the hosts of long persistent phosphors.The structure and properties of the material were characterized by powder X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,excitation and emission spectra,thermoluminescence?TL?techniques and electron paramagnetic resonance?EPR?.The microstructure of materials was explored to study the material's luminescence mechanism.Some constructive ideas were proposed,and some factors affecting the luminescence properties of the materials were suggested.The blue long persistent phosphors of Zn_1-?Al₂O_4-?were prepared with decay time of about 4 hours.The materials were attributed to the phase?PDF No.05-0669?of ZnAl₂O₄ according to the analysis of XRD.The excitation-emission spectra showed that the emission wavelength of the blue materials was located at 467 nm.TL curve showed that the suitable trap depth for Zn_1-?Al₂O_4-?are 0.756 eV and 0.802 eV,which were corresponded to O defectsV._O.and Zn defects V_Z'_n,respectively.Based on the energy band theory and the crystal defect theory,the mechanism of the material Zn_1-?Al₂O_4-?was explored.It was suggested that Zn defects acts as emission centers.And electrons will transition to excited state after being excited by UV light,and then the excited electrons will be captured by the positively charged oxygen vacancy defects.After being trapped,it will be slowly released with the emission of light.The green long persistent phosphors Zn_2-?SiO_4-?were prepared with decay time of about 22 hours.The materials phase were attributed to the phase?PDF NO.37-1485?of?-Zn₂SiO₄ according to the analysis of XRD.The materials has green emission at521 nm.Combining XPS analysis and the establishment of the defect equation,it was found that there were inherent defects Zn defects and O defects in the material.According to TL curves,the suitable defect depths in the material Zn_2-?SiO_4-?are 0.782eV and 0.846 eV,respectively.Combined with EPR spectrum,it was attributed to Zn defects and O defects,respectively.The mechanism of photo-luminescence of zinc deficiency persistent phosphor was explored.It was proposed that^V'Zn defects as emission centers after being irradiated with UV light,the electrons on the defects will be excited and transition from the ground state to the excited state,while forming electron-hole pairs in the lattice.Some excited electrons will be captured by the O defect,and holes will be stored by the Zn defect.Then holes and electrons will migrate in the crystal lattice and undergo a series of processes such as trap-release-trap-capture-re-release and finally recombine with the emission of light.The yellow long persistent phosphors SrZn_2-?-x(PO_4-0.5?-x)₂:xDy³⁺were prepared with decay time of about 6 hours.The materials phase were attributed to the phase?PDF NO.50-0159?of SrZn₂?PO₄?₂ according to the analysis of XRD.The material has yellow emission at 572nm,which belongs to the ⁴F_9/2 ⁴H_13/2 transition of the emission center Dy³⁺.Combined XPS,TL,EPR spectrum and the defect equation to analyzeDy^?_Zn defects,Zn defects,and O defects in the materials.Using the combination of energy band theory and crystal defect theory to establish the luminescence mechanism of materials.It was suggested that part of excited electron by UV light were relaxed to a lower energy excited state and would be captured and stored by O vacancy defects,then released under thermal disturbance and finally transition from Dy³⁺(⁴F_9/2)to the energy level(⁴H_13/2)with the yellow light.Specially,zinc vacancy defects will trap holes that migrate in the crystal lattice and prolong the time that holes meet electrons,which helps to improve the afterglow performance of the materials.