Enhanced infrared-to-visible up-conversion emission and temperature sensitivity in (Er~(3+),Yb~(3+), and W~(6+)) tri-doped Bi_4Ti_3O_(12) ferroelectric oxide

摘要

Strong up conversion (UC) luminescence at 527, 550, and 662 nm is compared under an excitation of 980 nm in single doped (Er~(3+)), co-doped (Er~(3+)/Yb~(3+)), and (Er~(3+)/Yb~(3+)/W~(6+)) tri-doped bismuth titanate (Bi_4Ti3O_(12)). For the co-doped system, the frequency (UC) emission intensity due to Er~(3+) ions is enhanced significantly in the green bands due to the efficient energy transfer from Yb~(3+) to Er~(3+) ions. Further increase in the emission intensity is seen with non-luminescent W~(6+) ions in the tri-doped system due to the modification in the local crystal field around the Er~(3+) ions, and is evidenced through a gradual change in the crystal structure of the host lattice with increasing W~(6+) content. The observed changes in the fluorescence lifetime and the associated energy transfer mechanisms are discussed. A progressive reduction of the lifetime of the ~4S_(3/2) levels of Er~(3+) ions from 72 to 58.7 μs with the introduction of Yb~(3+) and W~(6+) dopant increases the transition probability and enhances the UC emission intensity. The efficiency of the energy transfer process (η) in the co-doped and tri-doped systems is found to be 9.4% and 18.6%, respectively, in comparison to the single doped system. Temperature sensing based on the fluorescence intensity ratio (FR) technique shows high sensitivity (0.0123 K~(-1)) in the high temperature range (293 to 523 K) for an optimum content of Er~(3+), Yb~(3+), and W~(6+) with Jt = 0.03, = 0.18, and z = 0.06 at. % in the tri-doped Bi_(4-x- y)Er_xYb_yTi_(3_z)W_zO_(12) ferroelectric composition, and is found useful for potential applications in optical thermometry.