Optical Efficiency of Short Wave Infrared Emitting Phosphors

Several methods and corresponding parameters have been used to measure the emission intensities and efficiencies of luminescent materials (e.g., organic dyes, quantum dots, rare-earth-doped materials). The important performance parameters characterizing the emission intensities or brightness are overall quantum yield, intrinsic quantum efficiency, and radiant efficiency. Currently, the measurement parameter used to evaluate the brightness varies with the type of material (e.g., organic dyes vs rare-earth-doped phosphors) that is studied. Since different performance parameters are used, the relative performance among the different material classes cannot be compared easily. This work demonstrates that optical efficiency can be use as a single performance parameter to measure the short wave infrared (SWIR) emission performance of rare-earth-doped materials with different emission mechanisms and branching. NaYF4:Yb-Er (with visible upconversion emissions), CeF3:Yb-Er (no upconversion), ErGdVO4 (quantum cutting phosphor), and commercial Kigre phosphate glass were tested. Phosphors that emit on the basis of a quantum cutting mechanism were compared to those that emit through the single-photon downconversion mechanism. It was found that the optical efficiency of ErGdVO4 as a three-photon quantum cutting phosphor was poorer than any single-photon downconversion phosphor tested. NaYF4:Yb-Er, a single-photon downconversion phosphor, was found to emit most brightly. Its emission was similar to 2.5 times more efficient than the Kigre phosphate glass.