Infrared-to-Visible Conversion by Rare-Earth Ions in Crystals

Abstract

An analysis of infrared conversion to visible and ultraviolet radiation by Yb³⁺–Er³⁺, Yb³⁺–Ho³⁺, and Yb³⁺–Tm³⁺ ions in crystals is presented. The expression for the visible power output in the presence of back transfer from the active ion to the energy‐transferring ion (Yb³⁺) is given and the relationship between the intermediate state transfer and back transfer coefficients for maximum output is found. If this relationship is satisfied the visible output in the presence of back transfer is equal to the maximum output with no back transfer. The behavior of the power output when the transfer and back transfer coefficients depart significantly from this optimum condition is examined and the parameters which govern the power output under these conditions are determined. The analysis is applied to Yb³⁺–Er³⁺, Yb³⁺–Ho³⁺, and Yb³⁺–Tm³⁺ ions in BaYF₅ and BaY₂F₈. Measurements on the brightest composition of Yb³⁺–Er³⁺ ions in BaYF₅ indicate that the advantage of a long‐lived intermediate state is diminished by back transfer. A power‐conversion efficiency of 0.1% has been obtained for the green emission from BaYF₅:Yb³⁺–Er³⁺ when pumped by 0.93‐μ radiation from a 17% efficient Si–GaAs diode. Conversion efficiencies of 0.03% are obtained for the green emission from BaY₂F₈:Yb³⁺–Ho³⁺ and for the blue emission at 4800 Å from BaYF₅:Yb³⁺–Tm³⁺. Efficient conversion of 1.5‐μ radiation to the visible by BaYF₅:Er³⁺ is also described.