Research On Properties And Working Mechanism Of Rare Earths Doped Zirconium Salt Long Persistent Phosphor Materials

Long persistent luminescence?LPL?is a special photoluminescence phenomenon.LPL materials have attracted researchers'interesting since they are green luminescent materials with energy storage and energy saving.A lot of LPL materials were surveyed systematically,and the characterization of its structure and properties and a variety of luminescence mechanisms were systematically classified and summarized in this work.The zirconium phosphate and zirconium silicate with chemical stability were used as matrix materials and rare earth ions as activators.And a series of luminescent materials such as ZrSiO₄:Sm³⁺,ZrP₂O₇:Nd³⁺and ZrP₂O₇:Tb³⁺,Nd³⁺were prepared by high temperature solid state reaction.The XRD,XPS,excitation and emission spectra,decay curves and thermoluminescence?TL?spectra of the synthesized materials were characterized and analyzed.Based on the tests and analyses of the microstructure and properties of the materials,some constructive views on the luminescence mechanism of the materials were put forward,and some methods to improve the luminescence properties of the materials were summarized.Some meaningful research results were obtained.The main achievements are as follows:?1?The blueish-green LPL of ZrSiO₄:Sm³⁺with good luminescent properties was obtained by replacing Zr⁴⁺with Sm³⁺.XRD tests showed that the phase of the synthesized materials was attributed to the phase?PDF#06-0266?of ZrSiO₄.XPS characterization analyses indicated that there existed_OV^??,Zr^3?10?_Zr4?10?',Sm'_Zr andSm_Z'_r defects in the materials.TL spectra showed that the suitable trap depths of ZrSiO₄:Sm³⁺are 0.69eV and 0.79eV.The emission spectra showed that the d-d transition of Zr⁴⁺?blue light?and the ⁶H_5/2-⁴G_5/2transition of Sm³⁺?green light?made the main contribution to the blueish-green afterglow of the materials.The luminescence mechanism of the materials was established based on energy band theory and crystal defect theory.When excited by light,the electrons on the luminescence centers ofZr^3?10?_Zr4?10?',Sm'_Zr andSm_Z'_r defects jumped from the ground state to the excited state,and then were trapped by_OV^??through tunneling effect.Under thermal disturbance,the trapped electrons would slowly escape from_OV^??and jumped back to the ground state with the production of afterglow.?2?The blueish-green LPL materials of ZrP₂O₇:Nd³⁺with good luminescent properties were obtained by replacing Zr⁴⁺with Nd³⁺.The XRD tests showed that the phase of the materials was attributed to the phase?PDF#49-1079?of ZrP₂O₇.It was inferred that the oxygen vacancy(_OV^??),Zr^3?10?_Zr4?10?'andNd'_Zr defects were existed in the material lattice by XPS spectra and defect equations analyses.The emission peaks of the materials are mainly located at 466nm,485nm and 525nm,belonging to blueish-green light,in which 466nm and 485nm both belong to the d-d transition of Zr⁴⁺and the ²G_9/2-⁴I_9/2/2 and ⁴G_9/2-⁴I_9/2/2 transitions of Nd³⁺,while 525nm belongs to the ²G_7/2-⁴I_9/2/2 transition of Nd³⁺.TL spectra showed that the prepared material has trap level with appropriate depth.The luminescence mechanism of electron-hole pairs was established to understand the luminescence principle of the materials.Zr^3?10?_Zr4?10?'and Nd'_Zr together act as the luminous centers,the electrons onZr^3?10?_Zr4?10?'andNd'_Zr were excited and the electron-hole pairs were produced after illumination,and then the electrons and holes were captured by the defects.Under the action of thermal disturbance,the electrons and holes would be released from the defects and finally recombine to produce afterglow.?3?The yellowish-green LPL materials of ZrP₂O₇:Tb³⁺,Nd³⁺with good luminescent properties were obtained by the sensitization of Nd³⁺to ZrP₂O₇:Tb³⁺.XRD patterns showed that the phase of the synthesized materials can be assigned to the phase?PDF#49-1079?of ZrP2O7.It was inferred that there wereZr^3?10?_Zr4?10?',Tb'_Zr,Nd'_{Z r}and_OV^??defects in the crystal lattice of the materials by XPS spectra and defect equations analyses.The emission spectra showed that several emission peaks of the material were attributed to the Tb³⁺transitions of⁵D₃-⁷F₅?416nm?,⁵D₃-⁷F₄?435nm?,⁵D₄-⁷F₆?486 and 495nm?,⁵D₄-⁷F₅?541 and 548nm?,⁵D₄-⁷F₄?582nm?and ⁵D₄-⁷F₃?620nm?.The ⁵D₄-⁷F₅ transition of Tb³⁺made the main contribution to the luminescence of the material.There existed an energy level overlap between the ²G_9/2-⁴I_9/2/2 and ⁴G_9/2-⁴I_9/2/2 levels of Nd³⁺and the f-f level of Tb³⁺,illustrating that there existed the energy transfer from Nd³⁺to Tb³⁺for the improvement of the luminescent properties of the materials.TL spectra showed that the ZrP₂O₇:Tb³⁺,Nd³⁺materials had the suitable trap depth of 0.72eV.Based on the energy band theory,crystal defect theory and ion sensitization,the luminescence mechanism of the materials was established to understand the luminescence essences of the materials.Exposure to light,the electrons on theTb'_Zr and Nd'_Zr defects were excited.Most of the excited electrons would eventually and directly jump from the ⁵D₄ level of luminous center Tb³⁺to the ground state ⁷F₅ level with the emission of the yellowish-green light.Some electrons in the sensitizer Nd³⁺excited state would relax directly to the ⁵D₄ excited state of Tb³⁺and then jumped back to the ground state ⁷F₅ with luminescence to enhance the luminescence properties of the materials due to the sensitization of Nd³⁺.