Spectroscopic and photoluminescence properties of Ho doped Ba0.65Sr0.35TiO3 nanocrystals

Ho³⁺ doped Ba_0.65Sr_0.35TiO₃ (BST) nanocrystals was prepared by sol-gel method. The structural and morphological properties of the nanocrystals were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The absorption spectrum, photoluminescence spectrum and fluorescence time decay curve were measured at room temperature. Based on the Judd-Ofelt (J-O) theory, the J-O intensity parameters Ω_t (t=2, 4, 6) of Ho³⁺ doped BST nanocrystals were calculated to be 0.67×10⁻²⁰ cm², 1.11×10⁻²⁰ cm² and 1.09×10⁻²⁰ cm², respectively. The emission probabilities, radiative lifetimes and branching ratios of the different Ho³⁺ transitions were also determined. The emission cross sections of the important intermanifold transitions ⁵F₄,⁵S₂→⁵I₈, ⁵F₅→⁵I₈ and ⁵F₄→⁵I₇ have been calculated from the luminescence spectrum. The room temperature fluorescence lifetime of the ⁵S₂→⁵I₈ transition for Ho³⁺ in BST nanocrystals was measured and the radiative quantum efficiency was estimated to be 61.9%.