Synthesis, Microstructure And Optical Properties Of Er³⁺ Ions Doped 12CaO·7Al₂O₃ Ceramics

Er-doped 12CaO·7Al₂O₃ (C12A7:Er) transparent ceramics were prepared using chemical precipitation method combined with electrical beam ablation. X-ray diffraction (XRD), micro-Raman spectra, absorption spectra, emission spectra and excitation spectra were conducted to characterize the microstructure of C12A7:Er ceramics. The XRD and Raman results indicated that C12A7 ceramics with the cage structure were obtained. From absorption spectra, the absorption peaks related to Er³⁺ were observed, indicting the existance of Er³⁺ in the host of C12A7.The intense emissions from C12A7:Er ceramics with different Er concentrations in the visible region at room temperature were 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.Er³⁺ doped C12A7 ceramics have been synthesized, the absorption and transmittance spectra were measured and analyzed. Based on J-O theory, the intensity parameters ?t(t=2,4,6)were 5.30×10-20,5.48×10-20 and 0.47×10-20cm2, respectively. Then the radiative transition probabilities, radiative lifetimes and fluorescence branching ratio were calculated. It was observed that the ?2 parameter of Er³⁺ ions is larger, suggesting that the symmetry of Er³⁺ ions in ceramics was greatly distorted due to their incorporations into the Ca2+ site in C12A7 ceramics.The fluorescence spectra of Er³⁺ samples were studied. Er³⁺ samples upon excitation at 379 nm presented two visible emission bands, which were attributed to 2H11/2→4I15/2 and 4S3/2→4I15/2 transitions. According to the lifetimes and fluorescence branching ratios obtained by Judd-Ofelt theory, the radiative lifetimes of 4S3/2 level and fluorescence branching ratios of 4S3/2→4I9/2, 4I11/2, 4I13/2, 4I15/2 transitions were calculated to be 2.15ms and 15.5%,3.40%,24.00%,57.00%,respectively .Our results suggested that C12A7 was an appropriate candidate for Er doping, and had a potential applications in Er-doped laser materials, and full colour display.