Analysis of Energy Transfer and Infrared-to-Visible Conversion in LaF3:Yb, Er

Abstract

A model of the energy transfer between Yb³⁺ and Er³⁺ in LaF₃ which explains the efficiency and time dependence of the conversion of infrared excitation to visible emission in this material is presented and analyzed. It is concluded that in La_0.86Yb_0.12Er_0.02F₃ the probability of an excited Yb³⁺ ion transfering its energy of excitation to an Er³⁺ ion is at least an order‐of‐magnitude greater than the probability of the Yb³⁺ ion decaying with the emission of radiation or phonons. Similarly, an Er³⁺ excited to its ⁴I_11/2 state is much more likely to lose the energy of excitation by radiationless energy transfer to a Yb³⁺ ion than by other means. The decay time of the emission from the ⁴S_3/2 state of the Er³⁺ ion in La_0.86Yb_0.12Er_0.02F₃ was measured to be 140±20 μsec if the Er ion is excited directly in the ²H_11/2 or ⁴F_7/2 states while the same emission decays with a time constant of 1.1 msec when the phosphor is excited with infrared absorbed by the Yb³⁺ ions.