Inorganic Phosphors

Over the years literally hundreds of inorganic phosphors have been developed, a very large number of which have been commercialised. Only some of the more important ones, from a colour producing perspective, are discussed below. Detailed accounts of the major classes can be found in relatively recent publications.  

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Detection in CC may be visually for coloured compounds. Different methods can be used to monitor colourless compounds (collecting fractions addition of an inorganic phosphor to the column adsorbent). The detector choice is quite limited, with UV, RI and molecular fluorescence (F) emission being the most popular. A fluorescent column adsorbent is extremely... 

It is worth noting some historical aspects in relation to the instrumentation for observing phosphorescence. Harvey describes in his book that pinhole and the prism setup from Newton were used by Zanotti (1748) and Dessaignes (1811) to study inorganic phosphors, and by Priestley (1767) for the observation of electroluminescence [3], None of them were capable of obtaining a spectrum utilizing Newton s apparatus that is, improved instrumentation was required for further spectroscopic developments. Of practical use for the observation of luminescence were the spectroscopes from Willaston (1802) and Frauenhofer (1814) [13]. 

Several microbial species (in particular fungi) produce phytases (EC 3.1.3.8). The incorporation of suitable, microbially derived phytases in the diet can confer the ability to digest phytic acid on the recipient animals. This would have a threefold beneficial effect the anti-nutritional properties of phytic acid would be destroyed a lesser requirement for feed supplementation with inorganic phosphorous wottld exist and reduced phosphate levels would be present in the faeces. Several trials have confirmed that the inclusion of phytase in animal feed promotes at least some of these effects. However, the enzyme is not yet used in many cormtries. This may be explained, in part, by the fact that most microbial species only produce low levels of phytase activity which, obviously, has an effect on the cost of the finished product. It seems likely that widespread utilization of phytase within the industry will only be made possible by the production of this enzyme from recombinant sottrces, and at least two major enzyme companies are marketing such an enzyme for a nttmber of years now. 

In 1895 Rontgen used barium platinocyanate to make X rays visible. This discovery led to the first industrial breakthrough for inorganic phosphors. In 1887 Verneuil recognized the significance of heavy-metal impurities for the luminescence of inorganic compounds. 

In the 1900s inorganic phosphors gained increasing scientific and industrial interest. In 1903 and 1904 Lenard and Klatt reported the connection between activators and light emission [5.298],... 

The luminescence of inorganic phosphors is comprised of the following processes 1) absorption and excitation, 2) energy transfer, and 3) emission. 

Pyrophosphates may hydrolyze to inorganic phosphoric acid (phosphate) and an organophosphoric acid. 

The most familiar display is a television or visual display unit associated with a computer. Both are based on the mature cathode ray tube (CRT) technology, whereby an electron beam selectively activates red, green, and blue (RGB) inorganic phosphors. It is an emissive technology and therefore produces bright images. 

It is believed that the major part of inorganic phosphor absorption in the intestine occurs via Na+-dependent phosphate cotransporter NaPi-Iib (SLC34A2, Xu et al. 1999). Small drugs like phosphocarbonic acid and foscamet are transported by this transporter (Swaan et al. 1995 Tsuji and Tamai 1996). However, the substrate range is rather limited including only inorganic phosphate compounds. 

Detection and Identification Detection and identification of solute bands is done by methods essentially the same as those described in Column Chromatography. However, in TLC an additional method cal led fluorescence quenching is also used. In this procedure, an inorganic phosphor is mixed with the adsorbent before it is coated on the plate. When the developed chromatogram is irradiated with ultraviolet light, the surface of the plate fluoresces with a characteristic color, except in those places where ultraviolet-absorbing solutes are situated. These quench the fluorescence and are detectable as dark spots. 

Inorganic phosphors can have their luminescent efficiency improved by the addition of an activator, e.g., 0.1% T1 in Nal (then referred to as Nal(Tl) excitation energy of Nal molecules is transferred to impurity centres in the crystal lattice, which de-excite with photoemission characteristic of the impurity. The higher atomic number of these phosphors improves the probability of photoelectric effect events. Nal is deliquescent and has to be sealed in an A1 pot with glass window. The useable light output is improved by painting white to improve reflection from the surface. 

Other groups reported the solution synthesis of a cerium-doped inorganic phosphor library (73) to optimize their structure as luminescence down-converters in white Light Emitting Diodes (LEDs) and the use of cathodoluminescence (CL) (74) to identify... 

Dexter DL, Schulman IH. Theory of concentration quenching in inorganic phosphores. 1. Chem. Phys. 1954 22 1063-1070. 

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