Ultraviolet radiation light incident

Photoluminescence involves excitation by electromagnetic, often ultraviolet, radiation. Also used generically for all those processes that absorb incident light and later re-emit part of that energy as visible light. 

Certain compounds, when excited in solution by visible or near ultraviolet radiation, re-emit all or part of this energy as radiation. According to Stokes law, the maximum of the spectral emission band is located at a higher wavelength than that of either the incident radiation or the excitation band maximum (see Figs I2.l and 12.2). After excitation, the intensity of the emitted light decreases (decays) exponentially according to equation (l2.l), which relates the instantaneous intensity to time ... 

When polystyrene films are exposed to ultraviolet radiation of 235.7 nm in vacuo, crosslinking occurs and the sample becomes partly insoluble [41]. Grassie and Weir [42] have performed a detailed investigation of the photolysis of polystyrene in vacuo as a preliminary step to the study of the photo-oxidation of that polymer. They found that the only gaseous product formed is hydrogen with a quantum yield of 4.3 x 10 2. The rate of the reaction increases linearly with the intensity of the incident light... 

Sunblocks are opaque substances such as zinc oxide, titanium dioxide, and iron oxide that protect by forming a shield on the skin, which reflects and scatters incident radiation. In essence, sunblocks provide physical protection against sun exposure, including both visible and ultraviolet light. Sunscreens are substances that chemically absorb ultraviolet light in the top layer of the epidermis, protecting the underlying layers. 

To study the ultraviolet or visible absorption spectroscopy of a solid material, the radiation reflected from the surface of the sample is detected and recorded as a function of the incident wavelength. The fraction of light reflected from a sample surface is given by... 

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