Local microstructure and photoluminescence of Er-doped 12CaO·7Al2O3 powder

Er-doped 12CaO·7Al₂O₃ (C12A7:Er) powders were prepared using the sol-gel method followed by annealing inorganic precursors. X-ray diffraction (XRD), Raman and absorption spectra revealed that Er ions existed and substituted Ca²⁺ lattice site in C12A7. The photoluminescence of C12A7:Er at room temperature was observed in the visible and infrared region using 488 nm (2.54 eV) Ar⁺ line as excitation source, respectively. The sharp and intense green emission bands with multi-peaks around 520 nm and 550 nm correspond to the transitions from the excited states ²H_11/2 and ⁴S_3/2 to the ground state ⁴I_15/2, respectively. Furthermore, red emission band around 650 nm was also observed. It was attributed to the electronic transition from excited states ⁴F_9/2 to the ground state ⁴I_15/2 inside 4f-shell of Er³⁺ ions. The intensive infrared emission at 1.54 μm was attributed to the transition from the first excited states of ⁴I_13/2 to the ground state (⁴I_15/2). The temperature dependent photoluminescence of infrared emission showed that the integrated intensity reached a maximum value at near room temperature. The forbidden transitions of intra-4f shell electrons in free Er³⁺ ions were allowed in C12A7 owing to lack of the inversion symmetry in the Er³⁺ position in C12A7 crystal field. Our results suggested that C12A7:Er was a candidate for applications in Er-doped laser materials, and full color display.