Phosphoroscope, Becquerel

Thomas and Colbow (59) have described an elegant method by which one can change the angular position between the slits in a Becquerel phosphoroscope. Their system uses separate mechanical chopping of the... 

Another simple modification of the Becquerel phosphoroscope was described by Lewis and Kasha (60). Here one has a cylinder which can be rotated at various speeds with the sample inside. The cylinder contains a window and the exciting light source is placed on one side of the cylinder, with the detector on the other. When the window faces the source the sample is excited, and when it faces the detector the intensity is measured. The time between excitation and detection can be changed by altering the speed of rotation. In this manner the complete decay curve can be plotted. Again it... 

Figure 11. Improved version of the Becquerel phosphoroscope [from Ref. (59)].

A sophisticated type of Becquerel phosphoroscope, utilizing electronic flash circuitry and photomultiplier gating has been reported by Peterson and Bridenbaugh (61). This device appears to be quite useful and is representative of a large number of similar instruments. For these two reasons it is considered in some detail. Figure 13 is a schematic diagram of the system. 

Chloroplasts were prepared from spinach leaves with STN solution (sucrose 0.4 M, tricine 20 mM, pH 7.4, NaCl 0.01 M) as before (Wei, 1980). ms-DLE were measured with a Becquerel phosphoroscope. The dark intervals used between the 1 ms illumination on the chloroplast suspension and the 1 ms DLE measurement were 1.8 ms. The flashing light intensity from a mirror incandecent lamp through the hole of the rotating disk at the surface of the cuvette of chloroplast suspension was 5 x 10 erg-cm". s " , which was strong enough to saturate the rate of Hill reaction. 

Edmond Becquerel (1820-1891) was the nineteenth-century scientist who studied the phosphorescence phenomenon most intensely. Continuing Stokes s research, he determined the excitation and emission spectra of diverse phosphors, determined the influence of temperature and other parameters, and measured the time between excitation and emission of phosphorescence and the duration time of this same phenomenon. For this purpose he constructed in 1858 the first phosphoroscope, with which he was capable of measuring lifetimes as short as 10-4 s. It was known that lifetimes considerably varied from one compound to the other, and he demonstrated in this sense that the phosphorescence of Iceland spar stayed visible for some seconds after irradiation, while that of the potassium platinum cyanide ended after 3.10 4 s. In 1861 Becquerel established an exponential law for the decay of phosphorescence, and postulated two different types of decay kinetics, i.e., exponential and hyperbolic, attributing them to monomolecular or bimolecular decay mechanisms. Becquerel criticized the use of the term fluorescence, a term introduced by Stokes, instead of employing the term phosphorescence, already assigned for this use [17, 19, 20], His son, Henri Becquerel (1852-1908), is assigned a special position in history because of his accidental discovery of radioactivity in 1896, when studying the luminescence of some uranium salts [17]. 

Edmond Becquerel is the father of Henri Becquerel, who discovered radioactivity. Edmond Becquerel invented the famous phosphoroscope that bears his name. He was Professor at the Museum National d Histoire Naturelle and at the Conservatoire National des Arts et Metiers in Paris. 

It was Alexandre-Edmond Becquerel, in his 1867 treatise La Lumiere, ses causes et ses ejfets, who first put forward a systematic distinction between fluorescence and phosphorescence. Becquerel designed a phosphoroscope that allowed precise time intervals to elapse between the exposure of a material to light and the observation of the light emitted. He defined fluorescence as emission of light that is immediately extinguished upon removal of the light source, whilst phosphorescence persists for some time after exposure. 

Historically, one of the first known references on luminescence dates from the Chinese literature of the years 1500-1000 bc, where the phenomenon of light coming out from different types of glowworms is described. However, it appears that the first reported observation of photoluminescence can be traced back to the sixteenth century when a Spanish physician and botanist, Nicolas Monardes, reported a blue tint that appeared in the water contained in cups of a special type of wood. Edmond Becquerel (1820-91) was, during the nineteenth century, the most important researcher on phosphorescence phenomenon he not only obtained the excitation and emission spectra from different phosphors, but also performed many different fundamental studies including the effect of temperature or the measurement of the emission time of the phosphorescence phenomenon and established a exponential law to explain the decay of the phosphorescence emission. For such purposes he built in 1858 the first phosphoroscope that was able to measure lifetimes as short as 10 . ... 

Figure 3 A conventionai rotating-disk (Becquerel type) phosphoroscope. (Reprinted with permission from Fischer RP and Winefordner JD (1972) Analytical Chemistry44-. 949. American Chemicai Sociefy.)...

From a scientific point of view we recall that already in 1858, the phosphoroscope of Edmond Becquerel could be used for times as short as... 

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