Optimizing the upconversion photoluminescence of Er–Nb co-doped Bi4Ti3O12 ceramics by Ti divacancy defects

To optimize the upconversion photoluminescence (UCPL) performance of rare-earth doped Bi4Ti3O12 Aurivillius-phase ceramics, it is critical to reveal the microstructure-property relationship. In this work, Er and Nb co-doped Bi3.7Er0.3NbyTi3−yO12 (y=0,0.01,0.02,0.04,0.06) ceramics were synthesized via a solid-state reaction. The x-ray diffraction analysis confirmed their phase-pure orthorhombic without a secondary phase. Compared to Bi3.7Er0.3Ti3O12, the intensities of 528 and 661 nm emission peaks of UCPL spectra for Bi3.7Er0.3Nb0.02Ti2.98O12 are 2.5 and 2.2 times increased, respectively. Experimental and theoretical calculation results of positron annihilation lifetime spectroscopy and coincidence Doppler broadening revealed the presence of VTi monovacancy and VTi–Ti divacancy defects within these ceramics. As demonstrated by the UCPL and the positron annihilation results, the enhancement of UCPL performance of Er–Nb co-doped Bi4Ti3O12 ceramics is predominantly determined by the VTi–Ti divacancy defects.