The Study Of The Change In Encaged Anions On Sr²⁺-Doped 12CaO·7Al₂O₃ By Euion Fluorescent Probe

12CaO·7Al₂O₃（C12A7） served as one kind of multi-functional materials, has unique cage structure and it has great potential in the application because it can be converted from insulator to semiconductor, conductor, and superconductor by simply changing the encaged anionic species and their concentrations. 12 SrO·7Al₂O₃（S₁2A₇） shows the similar nanocaged structure as C12A7 and has larger lattice parameters（a = 12.322 ?） than C12A7（a = 11.974 ?）. The larger cages can accommodate larger anions, and is good to the exchange of the anions. The doped Sr²⁺ in C12A7 could take the place of Ca2+, making the cage size larger. The main phase of Sr²⁺ doped C12A7 is similar with that of C12A7 and it has good thermo-stability at high temperature. Thus it can make the encaged anion in Sr²⁺ doped C12A7 exchanged easier.CaCO₃, SrCO₃, Al₂O₃, Eu₂O₃ were used as raw materials in this paper through high temperature solid phase reaction method in air to prepare C12A7: x % Sr, 0.3% Eu（x =0,1,3,5） powder. XRD and PL results suggested that Sr²⁺ is successfully incorporated into C12A7 and Eu³⁺ has two kinds of sites in C12A7. With the increase of doped Sr²⁺, the similar behavior can be observed. C12A7 with O₂- and O- as encaged anions is proved through the ESR. With the increase of Sr²⁺, concentration of encaged O₂- and O- are increased, and the ratio of O- and O₂- is changed. From the luminescence decays of the 5D0â†'7F₂ transition of Eu³⁺ monitored at 619 nm, all the decays of Eu³⁺ can be sorted into two components, suggesting that Eu³⁺ ions have two different surroundings. One is related to O₂- in the vicinity, having a relatively long decay time, and the other is related to the encaged O- with a short decay time. With the increase of Sr²⁺, the size of the cage structure increases gradually and it promotes the O₂-（cage）+ O₂（g）= O-（cage）+ O₂-（cage） reaction, to increase the concentration of O- and O₂-.To understand the dependence of the exchange of encaged anions on the Sr²⁺ doping, the samples were annealed under different atmospheres（O₂, air, and H₂）. The samples annealed in oxygen and in air showed the existence of Eu³⁺, but part of the doped Eu³⁺ ions was reduced to Eu²⁺ in hydrogen atmosphere. The integral intensity ratio of Eu²⁺to Eu³⁺ is increased with the increasing of Sr²⁺ concentration, suggested that Sr²⁺ doping in C12A7 can promote the reduction of europium ion under the same annealing conditions. By detecting the decay time of Eu³⁺ and Eu²⁺ in hydrogen atmosphere, all the Eu³⁺ decay can be sorted into twocomponents, attributed to H- and O₂-, respectively. They increased with increasing concentration of Sr²⁺, but is shorter than those in air. Because of the reaction of H₂（g）+O₂-（c）=H-（c）+OH-（c） leads to the increasing of OH-, it can speed up the nonradiative transition process of all the Eu³⁺ and makes the lifetime shorter than those in the air. With the increase of concentration of Sr²⁺, the cage of C12A7 becomes larger. It promoted the reaction of H₂（g）+O₂-（c）=H-（c）+OH-（c）, and produced more OH-. The above results suggested that the incorporation of Sr²⁺ is help to exchange encaged anions in different atmospheres.