Design And Properties Of Yellow And Cyan Long Persistent Luminescence Materials Sensitive To Human Eyes

For visible Persistent luminescence?PersL?materials,it is mainly applied to weak light illumination.In the dark field environment(10^-610^-22 cd/m²),the maximum visual sensitivity of the human eye is at 507 nm?visual relative sensitivity is 100%?and the wavelength range of human eye sensitivity is 400-600 nm,which involves violet to orange light.At present,the comprehensive performance of blue and green PersL materials have reached the requirements of commercial application.In order to realize the multicolour of PersL materials sensitive to human eyes and the wider commercial applications,this thesis mainly focuses on the development of yellow and cyan PersL materials and the research of PersL performance.Yellow PersL materials:a series of Ca₆BaP₄O₁₇:Eu²⁺,RE³⁺with excellent yellow PersL properties were prepared by a conventional high-temperature solid-state method.Among them,for Ca₆BaP₄O₁₇:Eu²⁺,Ho³⁺,the initial brightness reaches 130 mcd/m²and the duration time exceeds 47 h?>0.32 mcd/m²?after 10 min excitation with 254nm light source.We also studied the effects of Ho³⁺ions concentration on photo-luminescence?PL?,PersL decay curve and thermoluminescence?TL?characteristics.Based on this work,the trap distribution of Ca₆BaP₄O₁₇:Eu²⁺,RE³⁺?RE=Dy,Tb,Ce,Gd,Nd?and the specific process of PerL decay were analyzed in detail by using PersL spectrum,PersL decay curve as well as TL spectrum under different decay time.The results show that the trap distribution and the specific PersL decay process are different for codoping different RE³⁺ions.In addition,considering that high pressure is an effective means to study the energy band and energy level structure of materials,we studied the variation of PL and PersL performances of Ca₆BaP₄O₁₇:Eu²⁺,Tb³⁺under high pressure.When the pressure is⁰.15 GPa,the PL intensity and PersL decay time performances reach the best.Cyan PersL materials:a series of Ca₃?PO₄?₂:Eu²⁺,Dy³⁺,BaZrSi₃O₉:Eu²⁺,Pr³⁺,K₂Ba₇Si₁₆O₄₀:Eu²⁺,Nd³⁺,Ba₂Zr₂Si₃O₁₂:Eu²⁺,Nd³⁺were prepared by high-temperature solid-state method.The main results are as follows:1.After 10 min excitation with 254 nm light,the initial brightness of Ca₃?PO₄?₂:Eu²⁺,Dy³⁺reaches 360 mcd/m² and cyan PersL could exceed 5 h??0.32 mcd/m²?.We observed an abroad emission band peaking at 480 nm which is ascribed to the 4f⁶5d¹to 4f transition of Eu²⁺ions and a sharp peak at 575 nm corresponding to the⁴F_9/2/2 to⁶H_13/23/2 transition of Dy³⁺ions in PL and PersL spectra.In other words,the energy transfer from Eu²⁺ions to Dy³⁺ions is realized in both PL and PersL processes.2.The emission peak of BaZrSi₃O₉:Eu²⁺,Pr³⁺is located at 478 nm.After 10min excitation with 254 nm light,the cyan PersL decay time of the optimal sample is more than 15 h.Through the influence of excitation duration time,decay time and excitation temperature on the TL spectrum,the specific pattern of electron capture and release in the PersL decay process is revealed.That is,the electrons in the deep trap directly transfer to the excited state of Eu²⁺ions with lower energy through the tunneling effect,while the electrons in the shallow trap migrate to the excited state of Eu²⁺ions with higher energy through the conduction band?CB?.The electron transition from the excited state to the ground state brings forth cyan PersL.3.The emission peak of K₂Ba₇Si₁₆O₄₀:Eu²⁺,Nd³⁺is located at 500 nm.After254 nm light charging for 10 min,the PersL decay time of the optimal sample exceeds10 h.Moreover,the PL,PersL and TL analysis were systematically studied,especially the relationship between the above properties and the trap distribution was clarified.A large number of suitable traps are produced by codoping Nd³⁺ions,which significantly improve the PersL performance,the PL intensity and thermal stability.4.After 10 min excitation with 254 nm light,the PersL initial brightness reaches155.5 mcd/m² and the decay time reaches 25 h of Ba₂Zr₂Si₃O₁₂:Eu²⁺,Nd³⁺.The band structure of Ba₂Zr_2-xHf_xSi₃O₁₂2 was adjusted by partially replacing Zr⁴⁺with Hf⁴⁺ions.Meanwhile,the energy gaps of the excited states of Eu²⁺ions and the trap center with respect to the CB were regulated,thus affecting the thermal stability and PersL performance.We have successfully regulated the trap distribution of Ba₂Zr₂Si₃O₁₂:Eu²⁺,Nd³⁺,and the trap depth can vary between 0.66-0.75 eV.For the optimal sample?x=0.5?,the PersL initial brightness is 131.3 mcd/m²,and the decay time is 31 h.