TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The system is a photovoltaic device (preferably solar cell or LED), a lasing medium, a sensor (preferably a chemical sensor or a temperature sensor) or a label preferably in biological/biochemical systems.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The first and the second components are first and second organic compounds. 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 compounds are carbon-containing compounds, provided that it is not a hydrogen-free chalcogenide of carbon or its derivative, a salt-like carbide, a metallic carbide or a metal-carbonyl. The emissive component's emitting energy at the second wavelength region lambda 2 is due to an up-conversion process based on a triplet-triplet annihilation process between photo-excited molecules of the emissive component and/or based on a triplet-triplet annihilation process between photo-excited molecules of the first component. The second wavelength region is -360 to 750 nm and the first wavelength region is -500 to 1500 nm. The first component is an organic dye (preferably two-photon absorbing dye), an optical limiting compound, a fullerene, carbon nanotubes, inorganic nanoparticles or inorganic nanocrystals. The second component is an organic dye or an inorganic emissive component. At least one of the first and second components is an organic dye. The first component is a first organic dye and the second component is a second organic dye, where the first and second organic dyes are same or different. The first and/or second organic dyes is/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 and organic dyes capable of hot-band absorption. The first and/or second organic dyes is/are styryl dyes, benzothiazole-containing two-photon chromophores, polyfluorenes, polyparaphenylenes, porphyrins, phthalocyanines, phthalocyanine complexes, xanthenes or rhodamines. The first organic dye is compounds showing non-liner absorption characteristics, preferably optical limiting compounds, e.g. two-photon absorbing (TPA) dyes (preferably porphyrins and phthalocyanines, including metalloporphyrins, metallophthalocyanines, porphyrin complexes, phthalocyanine complexes, dimers/polymers and arrays of porphyrin or phthalocyanine molecules) and the second organic dye is compounds showing fluorescence emission of 360-750 nm, in particular fluorescent dyes showing fluorescence emission of 360-750 nm, e.g. polyfluorenes and oligofluorenes (with or without any side-chain pattern) and their copolymers, polyparaphenylenes, including polyparaphenylene vinylene, and polyphenylene ethinylenes. The first organic dye is a porphyrin or metalloporphyrin, in particular octaethylporphyrin-palladium (or -platinum or -zinc or -copper), and the second organic dye is a polyfluorene or oligofluorene with or without (different) side chain patterns, in particular poly(7-(9,9-bis(2-ethylhexyl)fluorene)). The first and second components are dispersed into a matrix, where the matrix does not take part in an up-conversion process. The first component is dispersed into a matrix formed by the second component or vice versa. The first component forms a first layer and the second component forms a second layer on top of or underneath the first layer. The first and second components form a multi-layer 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, where the first subset of layers is the same or different or partially the same as that of the second subset of layers. EXAMPLE - No suitable example given.