Abstract

Every substance is associated to emission of electromagnetic radiation whose peaks are essentially influenced by temperature. Hot bodies (i.e., at T >700 °C) emit electromagnetic radiation in the field of visible light (incandescent light). The radiation emitted by cold bodies (i.e., at normal ambient conditions) in the visible light range is defined as luminescence. Luminescent light is emitted by exciting substances by means of electron fluxes (e.g., those generated in a cathode ray tube), using photon fluxes associated to electromagnetic radiations with wavelengths lower than ~390 nm (fluorescence), by mechanical stress (triboluminescence), by small temperature increase (thermoluminescence) or by biological processes (bioluminescence).

The value of luminescence demonstrations in teaching is unique. Indeed, by illuminating specific minerals and other substances (such as chicken eggs, seashells, fossils, wood, scorpions, soda drinks) with non expensive ultraviolet (UV) lights, it is possible to introduce the audience to several scientific arguments. Among these, the most important are: a) the concept of radiation and electromagnetic spectrum, including the g- and x-ray as well as the radio wave extremes; b) the discovery and the essence of natural radioactivity; c) the concept itself of visible light and the nature of the colours; d) the adaptability of the human eyes to the environment; e) the principles of the atomic structure as well as the basic concepts of energy quantization, including the photoelectric effect; f) the basic aspects of black-body radiation.

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