Modification Of Eu²⁺ Activated Borate Long Afterglow Materials

In the field of long afterglow materials,at present,only green long afterglow materials can be used,and there is a serious shortage of orange or red long afterglow materials that can be used commercially.And the mainstream green long afterglow material is based on strontium aluminate matrix,for borate matrix long afterglow material,the atoms in the[BO₃]^3-group are combined with three oxygen atoms and boron atoms with SP² hybrid orbitals to form a planar regular triangle,making the[BO₃]^3-structure very stable,which can effectively improve the luminous efficiency and stability of the long afterglow material.In this paper,we use Eu²⁺and Dy³⁺to co-doped NaSr₄（BO₃）₃ to obtain a novel long-glow material with yellow luminescence emission wavelength at 588nm.By changing the concentration of co-doped rare earth ions,the photoluminescence intensity of the sample was changed and its quenching concentration was 2%.On this basis,according to the crystal structure parameters of the sample,the excitation and emission spectra,the theoretical critical transfer distance between the luminescence centers of the sample and the actual critical transfer distance in the experiment were 13.85?and 14.03?,respectively,which explained the reasons for concentration quenching emission.Then,in the afterglow curve test,the 2%doped sample was also obtained with the best afterglow performance.Finally,XPS test and thermoluminescence curve test show that the trap concentration in the 2%doped sample is higher than that of other doped samples,which can capture more transitioning electrons and produce better afterglow performance.In order to realize the demand of multicolor luminescence,Ba²⁺,Mg²⁺in the LiSr₄（BO₃）₃:Eu²⁺,Dy³⁺samples have been proposed to partially replace the lattice position of Sr²⁺in the original samples,respectively,and with the increase of the amount of substitution,the emission color was respectively realized to shift from orange blue to yellow（632nm-611nm）and from orange red to orange red（632nm-648nm）.It is known qualitatively through the formula of crystal field strength calculation that the change of emission peak position is due to the weakened or enhanced originally crystal field strength after the replacement of Sr²⁺lattice position by Ba²⁺of smaller ionic radius or Mg²⁺of larger ionic radius,which weaken or aggravate the cleavage of Eu²⁺level because blue shift and red shift of emission wavelength occur.The afterglow properties of the samples were observed after the excitation was stopped,and it was found that LiSr_3.76Mg_0.2（BO₃）₃:2%Eu²⁺,Dy³⁺are suitable materials for red afterglow luminescence according to the afterglow curve test and thermoluminescence curve test of samples substituted with two ions with different substituting amounts.On this basis,we use Nd³⁺to replace Dy³⁺co-doping,because the ion radius of Nd³⁺is closer to the substituted ion Sr²⁺of the matrix than Dy³⁺,so it can have a higher footprint in the crystal,which is conducive to leaving more defects inside the sample,so that more electrons with transitions can be captured.XRD refinement of LiSr₄（BO₃）₃:2%Eu²⁺,Dy³⁺and LiSr₄（BO₃）₃:2%Eu²⁺,Nd³⁺confirmed the above hypothesis.The afterglow curve and thermoluminescence curve test results of the sample also showed that the afterglow performance of the Nd³⁺co-doped sample was better than that of the Dy³⁺co-doped sample,which further confirmed our inference.The research methods and ideas in this work are expected to be practically applied in the future research and development of multi-color luminescence materials with long afterglow materials.