Strong up conversion photoluminescence in Er³⁺ doped Bi₄Ti₃O₁₂ ferroelectric materials prepared by sol–gel method

Bi₄Ti₃O₁₂ (BTO) doped with different concentrations of Er³⁺ was prepared using sol–gel method. Their structures and surface morphology were examined by X-ray diffraction, Raman spectroscopy and scanning electron microscopy, respectively. All XRD peaks can be indexed according to orthorhombic BTO phase, which is consistent with Raman measurement results. Strong upconversion green luminescence is observed in the Er³⁺ doped BTO powders pumped by 980 nm at room temperature. Three upconversion emission bands centered at about 525, 550 and 662 nm are due to the radiative relaxation of Er³⁺ from ²H_11/2, ⁴S_3/2 and ⁴F_9/2 to the ground level ⁴I_15/2, respectively. The upconversion emission mechanism of the samples were identified and analyzed. In addition, the doped BTO ceramics show obvious hysteresis loops, demonstrating the ferroelectric properties of the samples. These results illustrate the potential of this class of materials for photonic applications in optoelectronics devices.