Synthesis And Optical Properties Of Er-doped 12CaO·7Al₂O₃

Er-doped 12CaO·7Al2O3 (C12A7:Er) powders were prepared using chemical precipitation method. X-ray diffraction (XRD), micro-Raman spectra and absorption spectra were conduceted to characterize the microstructure of C12A7:Er powders. Photoluminescence of C12A7:Er powder was investigated at different temperature ranging from 80-300 K. The result of XRD indicated that polycrystalline C12A7 powders of single cubic phase were obtained. The Raman spectra showed that the cage structural C12A7:Er had been obtained. From absorption spectra, it revealed that Er3+ existed in the host of C12A7 and caused the absorption peaks. The photoluminescence of C12A7: Er in the visible region was observed by using 488 nm (2.54 eV) Ar+ line as excitation source at room temperature. The sharp and intense green emission bands with multi-peaks around 520 nm and 550 nm corresponded to the transitions from the excited states 2H11/2 and 4S3/2 energy levels to the ground state 4I15/2, respectively. Furthermore, a red emission band around 650 nm was also observed. It was attributed to the electronic transition from excited states 4F9/2 to the ground state 4I15/2 inside 4f-shell of Er3+ ions.From the temperature dependent photoluminescence of C12A7, the green emission lines were attributed to at least two types of Er3+ centers. The PL intensity might be affected by free oxygen species relative to Er3+ ions formed by charge compensation. The inverse temperature dependent photoluminescence performances from the upper level of 2H11/2 state and that from the lower level of 4S3/2 state implied that the thermalization or thermal equilibrium of electrons between the two closely emission states occurred.Sharp and intense Er-related emission from C12A7:Er powder with different Er concentrations in the visible region at room temperature was investigated by analyzing the local structure of Ca atoms in C12A7 and it revealed that cation sites with low symmetry of the host were beneficial to the photoluminescence of Er3+ ions. The forbidden transitions of intra-4f shell electrons in free Er3+ ions have been allowed in C12A7 due to lack of the inversion symmetry in the Er3+ position in C12A7 crystal field.Furthermore, by using different wavelengthes as excitation source including 488 nm, 808 nm, an infrared emission band around 1.54μm was observed. It was attributed to the electronic transition from excited states 4I13/2 to the ground state 4I15/2 inside 4f-shell of Er3+ ions.Our results suggested that C12A7 was an appropriate candidate for Er doping. Semultaneously, the results suggested that C12A7:Er was a candidate for applications in Er-doped laser materials, and full colour display.