Preparation And Properties Of Gallate Yellow Long Persistent Luminescence Materials

Long persistent luminescent(LPL)materials have attracted a lot of attention because they can be used for safety indication,weak lighting and decoration at night or under dim light conditions.Currently,blue and green LPL phosphors have been successfully commercialized due to their excellent performance,while the performance of yellow and red LPL phosphors is difficult to meet the application requirements.The development of yellow LPL materials is more difficult than other types of colors due to the long wavelength and narrow wavelength range of yellow light.In this thesis,we designed and synthesized two kinds of gallate yellow LPL materials to address the lack of yellow LPL materials and the unknown mechanism,and systematically investigated their properties and proposed a possible afterglow mechanism.The following are the main research contents and conclusions:The novel yellow long persistent luminescent phosphor Ca Ga₂O₄(CGO):Pr³⁺,Li⁺was synthesized by solid-state reaction method at 1400°C.The crystal structure,photoluminescence(PL),long persistent luminescence(LPL),thermoluminescence(TL)and Mechanoluminescence(ML)properties of this persistent luminescent material were systematically investigated.The crystal structure of Ca Ga₂O₄ can be described as the[Ga O₄]tetrahedrons connect with each other,forming large tunnels at the center,which is filled by Ca²⁺.Defects are likely to exist in such a structure which is also beneficial to the generation of LPL.The spectrum analysis shows the yellowish PL of CGO:Pr³⁺,Li⁺attributes to the transitions of Pr³⁺.However,the LPL of CGO:Pr³⁺,Li⁺,with yellow afterglow lasting for nearly 6 hours(above 0.32 mcd/m~2),is originated from Pr³⁺and the host.According to TL analysis,the traps of CGO:Pr³⁺,Li⁺mainly come from the intrinsic defects of CGO,and the doping of Pr³⁺could greatly increase the trap concentration.Moreover,co-doping of Li⁺as charge compensating agent and cosolvent can not only enhance the trap concentration,but also adjust the emission of LPL.The highly anisotropic crystal structure of CGO is the main cause of yellow ML.The similarity between ML and LPL spectra suggests that they have common emission centers.A novel yellow LPL material?-Sr Ga₂O₄:Bi³⁺was synthesized by high-temperature solid-phase method,and its crystal structure,energy band structure,photoluminescence,long persistent luminescence and thermoluminescence properties were investigated.Diffuse reflectance spectrum calculations show that the optical band gap of?-Sr Ga₂O₄is about 4.568 e V.The emission spectrum of?-Sr Ga₂O₄:Bi³⁺is a broadband emission centered at 565 nm in the range of 400-800 nm which is attributed to the ~3P₁?~1S₀transitions of Bi³⁺ions.The initial afterglow intensity of the?-Sr Ga₂O₄:0.01Bi³⁺sample was 0.266 cd/m~2 after three minutes of UV lamp irradiation,and the afterglow lasted for nearly four hours(?0.00032 cd/m~2).The analysis of the thermoluminescence curve indicates that there are three main traps in?-Sr Ga₂O₄:Bi³⁺with the depths of 0.678 e V,0.838 e V and 0.978 e V,respectively.The shallow trap with the depth of 0.678 e V is the main cause of the LPL phenomenon in this material,while the deep trap with the depth of 0.838 e V corresponds to a decrease in the intensity of the thermoluminescence curve after 12 h of only 18.6%,which indicates that the slow electrons release in the deep trap has the potential to act as a suitable trap for information storage.