Studies On The Manufacture Of Ultra-fine Powders, Relationship Between Structure And Performances, And Applications For Persistent Phosphorescent Materials Of Strontium Aluminate

Research status for the persistent phosphors of rare earth ions doped alkali earth aluminate was systemically summarized in this paper. The synthesis of ultra-fine phosphors, relationship between structure and performances, mechanism of persistent luminescence, mechanical luminescence and quenching, surface encapsulation of phosphor and its application in coatings for Eu²⁺,Dy³⁺ co-doped strontium aluminate-based phosphors were studied and investigated, respectively.Ultra-fine SrAl₂O₄: Eu²⁺,Dy³⁺ phosphors with good persistent luminescence properties were synthesized for the first time by the improved sol-gel method and the co-precipitation - microwave radiation method (MRM). The effects of process conditions on phosphor morphology, grain size and persistent luminescence were investigated. The research results of gol-gel method showed that the removal of NO₃^-from reaction solution by co-precipitation process can decease the using amount of citric acid and ruduce grain size of SrAl₂O₄: Eu²⁺,Dy³⁺ phosphors as well. SrAl₂O₄ phase begins to come out after sinteringing the dry gel for 2h at 1100℃ and pure SrAl₂O₄ phase come into being after sinteringing the dry gel for 2h at 1200℃. The doping of B will result in the increasing of grain size, but can effectively improve the persistent luminescence properties of SrAl₂O₄: Eu²⁺,Dy³⁺ phosphors. The research results of co-precipitation - MRM showed that adding dispersing agent in reaction solution can prevent the agglomeration of precursor particles and help to synthesize fine and reactive precursor. The precursor can be transformed to pure SrAl₂O₄ phase after being sinteringed for 30⁴0min in microwave chamber. The doping of B will result in the increasing of grain size, but can effectively improve the persistent luminescence properties of SrAl₂O₄: Eu²⁺,Dy³⁺ phosphors. The phosphors synthesized by above two methods have finer grain size, better persistent luminescence and higher critical quenching concentration of Eu²⁺ than that of solid-state reaction.The relationship between structure and performances for strontium aluminate-based phosphors was systemically studied for the first time. The research results for the effect of composition on the afterglow phosphorescence from SrAl₂O₄: Eu²⁺,Dy³⁺ phase showed that it is so difficult for Eu²⁺, Dy³⁺ to replace the positions of Sr²⁺ in Sr-rich SrAl₂O₄ phase that the concentration of luminescent central and trap are lowwer and trap depth are smaller in Sr-rich crystal lattice than that of Al-rich crystal lattice. It is this reason that makes Sr-rich samples show worseafterglow phosphorescence. The research results of the effect of phase composition on the afterglow phosphorescence from alkali earth aluminate-based phosphors showed that in Al-rich phases, the electron energy level of 5d for Eu is split more and the gaps of energy levels are larger than that of SrAl2O4 phase owing to the effect of bigger crystal field, and traps' concentration and depth are bigger than that of SrAl2O4 phase. So emission peak of phosphors transfer to blue region, and afterglow luminance and life increase with the increase of Al-rich phases in phosphors. The research results for the roles of Eu2+,Dy3+ in SrAl2O4: Eu +,Dy3+ phosphors showed that Eu2+ is not only luminescent central, but also afterglow central. The more the doping amount of Dy3+ is, the better the afterglow phosphorescence is. Dy3+and Nd3+ can form electron traps of suitable depth duo to their proper optical electro-negativity. The research results of the roles of additives doped in SrAl2O4: Eu2+,Dy3+ phosphors and its working mechanism indicated that the doping of these fluxes as H3BO3, ZnO2, SiO2 and Ca(H2PO2)2 can effectively improve luminescent intensity and prolong afterglow life of phosphors. The mechanism study showed that the adding of H3BO3 would not only decrease the activation energy of solid-state reaction, quicken solid-state reaction, promote the rare earth ions dope into crystal lattice, but also increase traps' depth and concentration of luminescent central and traps. The research results for the roles of crystal defects in SrAl2O4: Eu ,Dy phosphors showed that DySr can be electron trap, v0 can't be electron trap of suitable depth, but can increase the depth of electron traps - DySr. v"r can be hole trap and recombination central as well, but the change of its concentration does not arouse the obvious change of persistent luminescence.A new persistent luminescence mechanism model - electron transfer model was proposed for the first time in this paper. It was put forward in this new mechanism that light excitation would result in the ionization of Eu2+ ( Eu*Sr ) , from which electrons and holes (i.e. metastable Eu3+) should be produced. The electrons would be captured by electron traps - DySr directly or by conduction band, and Dy3+ will transfer to metastable Dy2+ ( ï¿¡>Xs>) after this process. The holes would be captured by hole traps -vg by valence band. The transition process of central to central for electrons from electron traps to recombination centrals causes the quick decay process of afterglow. The indirect transition process for electrons from electron traps to conduction band and then to recombination centrals causes the slow decay process of afterglow. The transformation from metastable Eu3+ and Dy2+ to Eu2+ and Dy3+ would occur after the recombination process.Mechanical luminescence (ML) and quenching for SrAl2O4: Eu2+,Dy3+ phosphors were systemically studied for the first time in this paper. ML results revealed that both the mechanical stress and the concentration of rare earth irons play important roles in phosphors' ML. The higher the mechanical stress and the concentration of the doped Dy3+ are, the better the ML performances are. From the results of mechanical quenching research, it can be found that a bigger mechanical force on phosphors will destroy crystal structure and result in fluorescence quenching and afterglow quenching. Fluorescence quenching and afterglow quenching have relationship with the defects of EuxSr, DySr and v"r , respectively, and the latter always appears prior to the former, becasue the defect structure for DySr and v"Sr is much more unstable than that of Eu*Sr.Technologies of inorganic encapsulation, organic encapsulation and inorganic-organic encapsulation were firstly used for the surface modification of SrAl2O4:Eu2+,Dy3+ phosphors in this paper. The effects of process conditions on film performances were investigated. The results showed that silica encapsulation can effectively improve phosphors' water resistance and temperature stability at a minimum loss of phosphorence, so can alumina encapsulation do but at a minor loss of phosphorence. MAPS/MMA encapsulation can improve phosphors' water resistance and oil proximity at a minor loss of phosphorence, so can SiO2-MAPS/MMA do but at a bigger loss of phosphorence.The water-bone coatings were manufactured by using the encapsulated phosphors as pigments and the acrylic latex as the binder, and the performances of the coatings were studied in this paper. The results showed that pigment/binder ratio, thickness of coating film, phosphor and its surface modification status played important roles on mechanic performances of coating film, persistent luminescence of coating film, stock stability of coatings, water resistance of coating film, and light resistance of coating films respectively.