Molten salt synthesized LaTa7O19:Er3+/Yb3+ with superior upconversion luminescence by KCl flux

Abstract

LaTa7O19(LTO):Er3+/Yb3+ upconversion luminescence (UCL) phosphors with hexagonal structure was successfully prepared by a molten salt synthesis using KCl as solvent. Increasing holding temperature from 825 to 1150oC, the LTO structure is transformed towards K2LaTa5O15(KLTO). At 1150oC, the sample is pure phase KLTO:Er3+/Yb3+. Increasing holding time at 825oC from 2 to 48 h, LTO phase first increases and then decreases. Increasing KCl flux mass at 825oC for 24 h, the KLTO structure is first transformed towards LTO, then the KLTO structure increases, and LTO:Er3+/Yb3+ grain size decreases. The highest green UCL integral intensity of LTO:Er3+/Yb3+ reached 89% of β-NaYF4:Er3+/Yb3+. The maximum relative temperature sensitivity of 0.866% K-1 is reached by using the luminescence intensity ratio (LIR) technique. LTO:Er3+/Yb3+ phosphors with excellent pure green UCL can be prepared by molten salt with KCl flux, which can be applied as display and temperature sensing.