TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The first component is a first organic compound or dye, and the second component is a second organic compound or dye. The first component is neither covalently bonded nor complexed to the second component. The first and second organic compounds are different compounds. The first and second organic dyes are the same or different. The first and second organic compounds are carbon-containing compound but is nor hydrogen-free chalcogenide of carbon or its derivative, salt-like carbide, metallic carbide, or metal carbonyl. The first and second organic dyes are organic dyes capable of direct and/or sequential two-photon excitation, organic dyes capable of direct and/or multi-photon excitation, organic dyes capable of non-linear absorption, or organic dyes capable of hot-band absorption, preferably styryl dyes, benzothiazole-containing two-photo chromophores, polyfluorene, polyparaphenylene, porphyrin, phthalocyanine, phthalocyanine complex, xanthene, or rhodamine. The first organic dye is a compound showing non-linear absorption characteristics such as optical limiting compound, e.g. two-photon absorbing (TPA) dye. The first organic dye is porphyrin or phthalocyanine including metalloporphyrin, metallophthalocyanine, porphyrin complex, phthalocyanine complex, dimer/polymer, or array of porphyrin or phthalocyanine molecules, preferably octaethylporphyrin-palladium (platinum, zinc, or copper. The second organic dye is a compound showing fluorescence emission in 360-750 nm such as fluorescent dye showing fluorescence emission in 360-750 nm, e.g. polyfluorene and oligofluorene (with or without side chain patterns) and their copolymer, polyparaphenylene (including polyparaphenylene vinylene), or polyphenylene ethinylene, preferably PF2/6. The first and second components are dispersed into a matrix that does not take part in an up-conversion process; or the first component is dispersed into a matrix formed by the second component, or the second component is dispersed into a matrix formed by the first component. The first component forms a first layer and the second component forms a second layer on top of or underneath the first layer, or the first and second components form a multilayer structure where the first component is present in a first subset of layers and the second component is present in a second subset of layers.Preferred Components: The emissive component's emitting energy at the second wavelength is due to an up-conversion process based on direct or sequential two-photon excitation or multi-photon excitation or on excitation of molecules populating high vibrational states. The second wavelength region is 360-750 nm, and the first wavelength is 500-1500 nm.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The first component may be inorganic nanoparticles or inorganic nanocrystals. The second component may be inorganic emissive component.