“…Reliable quantification of nanoparticles absorption, scattering, and emission activities is essential for rational materials characterization, design, and applications as these optical processes differ significantly in their causes, effects, and applications. As examples, metal oxide nanoparticles with strong scattering activities in the UV ranges has been used extensively as sun block, while plasmonic nanoparticles find utilities in biosensing due to their strong scattering in the visible to infrared wavelength range. − The applications of photoactive nanoparticles, referring to chromogenic and fluorogenic nanomaterials, are even more diverse, ranging from photocatalysis, − photoluminescence, − photodynamic therapy, − photoelectronics, − and photothermal energy harvesting, − just to name a few. For these applications, it is the absorbed photons, not the scattered photons, that are directly responsible for chemical reactions in photocatalysis, light emission in photoluminescence, and singlet oxygen generation in photodynamic therapy.…”