Concept

Phosphor thermometry

Phosphor thermometry is an optical method for surface temperature measurement. The method exploits luminescence emitted by phosphor material. Phosphors are fine white or pastel-colored inorganic powders which may be stimulated by any of a variety of means to luminesce, i.e. emit light. Certain characteristics of the emitted light change with temperature, including brightness, color, and afterglow duration. The latter is most commonly used for temperature measurement. The first mention of temperature measurement utilizing a phosphor is in two patents originally filed in 1932 by Paul Neubert. Typically a short duration ultraviolet lamp or laser source illuminates the phosphor coating which in turn luminesces visibly. When the illuminating source ceases, the luminescence will persist for a characteristic time, steadily decreasing. The time required for the brightness to decrease to 1/e of its original value is known as the decay time or lifetime and signified as . It is a function of temperature, T. The intensity, I of the luminescence commonly decays exponentially as: Where I0 is the initial intensity (or amplitude). The 't' is the time and is parameter which can be temperature dependent. A temperature sensor based on direct decay time measurement has been shown to reach a temperature from 1000 to as high as 1,600 °C. In that work, a doped YAG phosphor was grown onto an undoped YAG fiber to form a monolithic structure for the probe, and a laser was used as the excitation source. Subsequently, other versions using LEDs as the excitation source were realized. These devices can measure temperature up to 1,000 °C, and are used in microwave and plasma processing applications. If the excitation source is periodic rather than pulsed, then the time response of the luminescence is correspondingly different. For instance, there is a phase difference between a sinusoidally varying light emitting diode (LED) signal of frequency f and the fluorescence that results (see figure).

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Concepts associés (2)
Luminescence
vignette|Chimiluminescence du luminol. La luminescence est une émission de lumière dite « froide » par opposition à l'incandescence qui est dite « chaude ». La lumière émise par luminescence résulte d'interactions entre particules électriquement chargées. Dans les cas les plus fréquents, ce sont des transitions électroniques ayant lieu dans des atomes, des molécules ou des cristaux qui provoquent l'émission de photons.
Phosphor
A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or visible light, and cathodoluminescent substances which glow when struck by an electron beam (cathode rays) in a cathode-ray tube. When a phosphor is exposed to radiation, the orbital electrons in its molecules are excited to a higher energy level; when they return to their former level they emit the energy as light of a certain color.

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