ABSTRACT
Downconversion of one high-energy photon (i.e., photon with short wavelength and high frequency) to two or more low-energy photons (i.e., photons with long wavelength and low frequency) enables quantum efficiency (QE) to be more than unity. Investigations into such efficient photon frequency conversion not only promote potential applications in mercury-free fluorescent lamps, plasma display panel, new-generation of photovoltaic cells, etc. but also facilitate unveiling the energy-level structure in vacuum ultraviolet region of lanthanide (Ln) ions as well as the mechanisms of stepwise electronic transitions, resonant energy transfer (ET), cross-relaxation ET, energy migrations, cooperative ET, multiphonon relaxation, phonon-assisted ET, etc. Libraries of fluorescent materials activated by Ln ions and/or transition metal ions have been fabricated and successfully demonstrated for their merits of efficient quantum cutting, exhibiting an optimal internal QE close to 200% for visible photon emission and a maximum QE close to 400% in near-infrared photon emission. By conjugating with the numerous emerging materials and techniques, continuous optimization of fluorescent properties of multiphoton downconversion should further improve the colorful applications of quantum cutting.
