Spectroscopic and upconversion properties of Er3+/Yb3+-codoped KLTN single crystal

A high optical quality erbium and ytterbium codoped potassium lithium tantalate niobate single crystal is grown by top-seed solution growth method, and the crystal structure is confirmed to be 4 mm point group and P4/mbm space group by powder X-ray diffraction analysis. The ultraviolet–visible–near infrared absorption spectrum, upconversion fluorescence spectrum excited by 975 nm continuous wave laser, power dependence, and fluorescence decay curves of Er3+ ions in the crystal are measured at room temperature. The Judd–Ofelt (JO) intensity parameters are calculated using the JO theory and absorption spectrum. The relationship of JO parameters Ω4 < Ω6 of Er3+ in the crystal is different from the general trend of Ω2 > Ω4 > Ω6. The absorption cross sections and emission cross sections of H11/22, S3/24, and F9/24 levels are calculated. The upconversion mechanism of Er3+ in the crystal is discussed based on pump power dependence analyses and decay curves. The emission intensities exhibit quadratic behaviors against pump energy, which are verified by the deduction of transition rate equation model.

► We grew Er3+/Yb3+-codoped KLTN single crystal by TSSG method.
► It has typical absorption bands of Er3+ and Yb3+ in UV-VIS-NIR absorption spectrum.
► Green and red UC emissions are observed under 975 nm excitation.
► The ET processes from Yb3+ to Er3+ play an important role in the UC emissions.