Structural properties, Judd–Ofelt calculations, and near infrared to visible photon up-conversion in Er3+/Yb3+ doped BaTiO3 phosphors under excitation at 1500 nm

Abstract

The structural and up-conversion properties of BaTiO₃ phosphors doped with Er³⁺/Yb³⁺ have been studied. All phases were synthesized using the sol–gel process and characterized by X-ray powder diffraction (PXRD), Raman spectroscopy, optical absorption spectroscopy (Judd–Ofelt theory), and scanning electron microscopy (SEM). Photoluminescence (PL) and time-resolved luminescence measures were employed to monitor the photon upconversion (UC) process in the synthetized phosphors. The results of PXRD show that all synthesized phases crystallize in a perovskite structure, where rare earth ions replace both Ba²⁺ and Ti⁴⁺ cations. Raman spectra confirm the coexistence of both cubic and tetragonal phases. Photon UC was studied under excitation at 1500 nm. The emission spectrum shows a strong emission at 975 nm (⁴I_11/2 → ⁴I_15/2) and a weak emission at 660 nm (⁴F_9/2 → ⁴I_15/2). To unravel the mechanism of photon UC, the dependence of the emission intensity on the pump power of the incident laser was also measured. Furthermore, the decay curves for the 975 nm emission upon excitation at 1500 and 800 nm were also recorded. These results of our study point towards a GSA/ESA type mechanism for photon UC in this material.