Preparation And Properties Of Zn₂SnO₄:Cr³⁺ Long Afterglow Luminescent Materials

In recent years,near-infrared（NIR）long afterglow materials have made continuous development,especially transition metal Cr³⁺ion doped near-infrared long afterglow materials,which have received widespread attention due to their excellent near-infrared luminescent properties and enormous potential for development and application in fields such as biological imaging.However,compared with long afterglow materials in the visible light region,it still has some defects,such as a relatively single choice of matrix materials,mainly using gallate system as the host material,greatly limiting its practical application range;at the same time,efficient near-infrared long afterglow materials are also lacking.Therefore,exploring the near-infrared long afterglow materials of Cr³⁺ion doped non-gallate systems is of great value.In this thesis,a series of near-infrared long afterglow materials with different preparation parameters were prepared by the conventional high-temperature solid-phase method,using zinc stannate compound as the matrix material and Cr³⁺ion as the activator.In addition,their NIR long afterglow properties were improved by introducing co-doping ions Al³⁺and rare earth ions M³⁺（M:Eu,Gd,Tm）;the effects of preparation process and co-doping on luminescence and afterglow performance were systematically studied.The main research contents and results are as follows.（1）Zn₂SnO₄:Cr³⁺long afterglow materials with different Cr³⁺doping concentrations and sintering temperatures were prepared by high-temperature solid phase method.Under350 nm excitation,it was found that the sample had a wide emission band of 650-1200nm with its central emission peak at 800 nm;the results show that it is derived from the⁴T₂（⁴F）→⁴A₂ energy level transition of Cr³⁺ions.In addition,the sharp emission peak at703 nm corresponds to the ²E→⁴A₂ level transition of the Cr³⁺ion.The optimal sintering temperature and the optimal doping concentration of Cr³⁺were obtained experimentally,and the preparation process parameters of the sample were optimized.（2）Zn₂SnO₄:0.002Cr³⁺,y Al³⁺（y=0～0.07）phosphors were synthesized by high-temperature solid-phase method based on the optimized preparation process parameters by introducing Al³⁺co-doped ions.By changing the doping concentration of Al³⁺ions,it was found that under the excitation of 350 nm ultraviolet light,when y=0～0.007,the luminous intensity of the co-doped sample increased with the increase of doping amount.When the Al³⁺doping amount continues to increase by more than 0.007,the luminescence intensity of the sample decreases due to the concentration quenching effect,and the optimal fluorescence emission is reached at y=0.007.Through the afterglow spectrum and optical image,it can be seen that the fluorescence luminescence intensity and afterglow performance of the sample are improved by the introduction of Al³⁺ion co-doping.（3）In Zn₂SnO₄:Cr³⁺ phosphor,M3+（M: Eu,Gd,Tm）co-doped ions were introduced to prepare synthetic near-infrared long afterglow phosphors.The effects of different M3+ ion contents on their fluorescence luminescence performance and long afterglow performance were studied separately.The experimental results showed that with the increase of Eu3+ ion doping concentration,Zn2 SnO4:0.002Cr3+,Eu3+ samples fluorescence luminescence intensity increased.At the same time,it can also effectively improve the luminescence performance of near-infrared long afterglow.When Gd3+ ions were introduced,the luminescence intensity of the samples first increasing and then decreasing with the Gd3+ ion content.When the Gd3+ ion doping concentration is 0.002,the fluorescence luminescence performance is the best.The results indicate that the introduction of M3+（M: Eu or Gd）can effectively enhance the near-infrared luminescence of Cr3+ ions during the near-infrared long afterglow luminescence process,and also serve as a trap to enhance the long afterglow luminescence performance of the sample.However,when Tm3+ ions were doped,a new emission peak appeared.The emission intensity of Cr3+ ion decreases with the increase of doping concentration,and the emission intensity of Tm3+ ion increases with the increase of Tm3+ ion concentration.The results show that the introduction of appropriate amounts of Tm3+ can improve the luminescence performance of NIR long afterglow to a certain extent.