Design And Property Regulation Of Cr³⁺-doped InMgGaO₄ And AlMgGaO₄ Near-infrared Afterglow Phosphors

A series of Cr³⁺-doped InMgGaO₄ and AlMgGaO₄ near infrared?NIR?long afterglow phosphors are designed and successfully synthesized by a high temperature solid state method.Firstly,the spectral range is adjusted by changing the cation coordination environment and composition in the matrix.And the bidirectional regulation of the emission peak in the first biological window?650 nm⁹50 nm?is realized.The effects of crystal structure,coordination environment and crystal field on the luminescence properties of Cr³⁺were also analyzed.Secondly,long afterglow luminescence with more than 10 hours is obtained by changing the matrix composition,and the types and distributions of defects were analyzed in detail.Finally,by constructing the host referred binding energy?HRBE?diagram and vacuum reference binding energy?VRBE?of 4f energy level,the rare earth ions Eu³⁺,Sm³⁺and Yb³⁺are selected to provide trap centers for Cr³⁺,which further improves the afterglow intensity of the materials.The emission spectra of these materials are in good agreement with the first biological window with good afterglow characteristics,so there are potential application values in biological detection and bioimaging.?1?The near infrared phosphor InMgGaO₄:xCr³⁺were synthesized successfully.The crystal structure of InMgGaO₄ is rhombohedral,Mg²⁺and Ga³⁺are located at the 3a site with five coordinations and In³⁺is located at the 6h site with six coordinations.And one of the Mg/Ga-O bonds is much longer than others,which is is easy to be broken with the influence of surrounding environment.At first,Cr³⁺ions is introduced into the In³⁺sites and lead to the breakage of the[Mg/Ga-O]bond,which provide a variable crystal field environment for Cr³⁺ions.The emission spectra of Cr³⁺shift to the red and tuned from narrow to broad with increasing the Cr³⁺concentration.Secondly,the emission spectrum of Cr³⁺is further tuned by changing the matrix component.The crystal field strength will be enhanced with the increase of Al³⁺concentration due to the radius of Al³⁺is smaller than that of In³⁺,and the emission spectrum changes from wide to narrow.In addition,the long persistent luminescence property of Cr³⁺is enhanced obviously.Fanily,the emission spectra of these samples can be tuned between narrow peak and broad band continuously by controlling the concentration of Cr³⁺ions or Al³⁺ions,which provide a new way to select the matrix for Cr³⁺-doped near-infrared phosphors.?2?A series of near infrared phosphors AlMgGaO₄:xCr³⁺are successfully synthesized.The luminescence and afterglow properties of Cr³⁺have been investigated carefully.The occupation of Cr³⁺is analyzed by the change of crystal field and lifetime.The crystal field around Cr³⁺decreases gradually with increasing the Cr³⁺concentration.Under the strong crystal field,Cr³⁺substitutes for the regular[AlO₆]octahedron firstly and produces the sharp line emission peak,and then a broad emission band is produced with the decrease of crystal field.As the further weakening of crystal field,Cr³⁺is more likely to occupy the Mg²⁺and Ga³⁺sites in disordered octahedrons and generate two broad emission bands.There are many of Al_Mg^?electronic traps in the AlMgGaO₄ crystal due to the inversion between Al³⁺and Mg²⁺sites,and Cr^?_Mg electronic traps will be produced with Cr³⁺substituting into Mg²⁺sites.The thermo luminescence?TL?spectra shift to shallower due to the produce of the shallower Cr^?_Mg electronic traps.In addition,after 10h of continuous emission,the persistent luminescence intensities of AlMgGaO₄:0.03Cr³⁺ is still considerably high.According to the initial rise method,the depths of the trap centers can be well fitted by a linear indicating that the trap centers are distributed continuously.Fanilly,the emission spectra of these samples can match well with the biological window I,and the super-long-persistent luminescence is of great significance for biological imaging.?3?The 4f level of lanthanide cations can serve as trap centers for Cr³⁺and improve the persistent luminescence of Cr³⁺.Firstly,by constructing the host referred binding energy ?HRBE?and acuum referred binding energy?VRBE?diagram of 4f level in AlMgGaO₄, three different lanthanides(Eu³⁺,Sm³⁺and Yb³⁺)are selected as the electron traps for Cr³⁺.And then,a series of phosphors AlMgGaO₄:0.03Cr³⁺,zLn³⁺?Ln=Eu,Sm,Yb?are synthesized successfully,and the afterglow properties are analized carefully.The intensity of afterglow luminescence and thermo luminescence?TL?spectra of Cr³⁺ increases first and then decreases with increasing the Eu³⁺/Sm³⁺/Yb³⁺concentration.In addition,the TL spectra shift to the higher tempreture,which indicates that Eu³⁺,Sm³⁺ and Yb³⁺enriched the trap levels and improved the afterglow intensity of Cr³⁺.The results show that constructing VRBE diagram is an effective method to select co-doped lanthanides ions for the activator.