Exploring the Ultimate Efficiency in Infrared-to-Visible Converting Phosphors Activated with Er and Sensitized with Yb

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Abstract
Recently developed visible solid‐state light sources made by coating ir light emitting diodes with ir‐to‐visible converting phosphors appear technologically interesting. However, the ultimate performance of these devices has been uncertain since there was no accurate method for extrapolating the nonlinear characteristics of the phosphors. We have developed techniques for exploring the ultimate efficiencies of these phosphors by exciting them with a tightly focused YA1G:Nd laser operating at 1.06 μ. The results of a series of measurements on the brightest phosphormaterials available indicate that the ultimate efficiencies are strongly dependent on the host crystal material. Of the materials we have examined, the most efficient hosts are barium vttrium fluoride, BaYF5, and yttrium fluoride, YF3. The ultimate visible efficiency of the latter, defined as the ratio of visible emitted power to incident ir excitation power, is in excess of 24%. Based on these results and the known performance of GaAs ir light emitting diodes, we conclude that the over‐all performance of ir‐to‐visible converting phosphor‐diode devices should be comparable to the direct visible emitting GaP devices.