Daylight phosphors

Note that there are some materials which glow for hours after being excited. This is not due to phosphorescence but to the presence of traps, i.e.- lattice defects, put there deliberately during their manufacture, Such phosphors, notably CaS activated by various cations including Bi , eire sometimes called "daylight" phosphors since they can be excited by visible light. Once activated, they will glow for hours. 

Donor and acceptor levels are the active centers in most phosphors, as in zinc sulfide [1314-98-3] ZnS, containing an activator such as Cu and various co-activators. Phosphors are coated onto the inside of fluorescent lamps to convert the intense ultraviolet and blue from the mercury emissions into lower energy light to provide a color balance closer to daylight as in Figure 11. Phosphors can also be stimulated directly by electricity as in the Destriau effect in electroluminescent panels and by an electron beam as in the cathodoluminescence used in television and cathode ray display tubes and in (usually blue) vacuum-fluorescence alphanumeric displays. 

These bricks, after calcination with carbon and exposure to daylight, emitted a reddish glittering in the dark. These Bolonian stones, also named moonstones, particularly those from the Monte Patemo, remain among the most famous ones and were the subject of scientific interest during the next two centuries they were termed phosphor (Greek light bearer ). They are considered the first inorganic artificial phosphors [2-4], The first natural phosphor was dia-mant, whose luminescence was cited by Cellini in 1568 [5]. 

Infrared radiation can be detected by phosphors by various mechanisms. Upon excitation with UV radiation, ZnS Cu +, Co2+ emits an afterglow that is quenched by IR radiation, whereas ZnS Cu+, Pb2+ stores excitation energy and emits it spontaneously under the action of IR radiation. CaS Sm3 +, Ce3+ and SrS Sm3 +, Eu2+ only exhibit low fluorescence on excitation by UV radiation and daylight. Through the subsequent action of IR radiation these phosphors can be stimulated to emit green or orange-red light. 

Quinaldine A 1 to 1.5% solution of 3,5-diaminobenzoic acid dihydrochloride in 30% phosphoric acid is sprayed on the plate, which is then heated (100°C, 15 min) to yield fluorescent (green/yellow) spots under long-wave UV or (in case of high concentrations) brown spots in daylight. 

Some lamps, like the new triphosphor cool-white lamps, Vita-Lite and daylight lamps have more than one phosphor. The use of more than one phosphor... 

A 1 1 complex of [Eu(fod)3] and Michler s ketone emits red luminescence under daylight illumination.Chemical shifts in the NMR spectra of adducts of [Ln(fod)3(bipy)] and [Ln(fod)3(phen)] are dipolar in origin.[Eu(ttfa)3(phen)] (ttfa = thenoyltrifiuoroacetonate) has been doped into organically modified silicate matrices on reaction with hexamethyldisilazane, a composite phosphor with high emission intensity was formed.The first perfiuoroacetylaceto-nate complexes have been reported. " ... 

Vitamin E compounds can be detected (about 20 /tg) as dark spots in UV light. They appear violet and detection is appreciably more sensitive (0.02 /tg) on layers that contain 0.02% Na-fluorescein. Moreover, these are visible in daylight as reddish spots (limit of detection 2 fig). The same effect is produced by spraying with fluorescein or dichlorofluorescein reagent. Nonspecific visualization procedures for tocopherols and tocotrienols are based on spraying with sulfuric acid, molybdophosphoric add, antimony(V) chloride, dipyridyl-iron reagent, nitric add, and copper(II) sulfate-phosphoric add [1-4]. 

White LEDs are typically coated with the YAG Ce phosphor that eauses them to emit a whitish light. The Ce activator in YAG has an overlapping excitation-emission band, making it possible to use a blue LED to excite this phosphor. Indeed, the YAG Ce phosphor is "daylight" excited. That is, it luminesces in sunlight due to the blue radiation present. 

This is not a comprehensive listing of all of the phosphors investigated. The most important part for a color-television display is the brightness produced at the "Daylight" color, i.e.- the niumlnant-C color... 

Fig. 9.8 UV-vis diffuse reflectance and the PLE (4em = 501 nm) and PL (2ex = 365 nm) spectra of the as-prepared NaBaScSi207 o.iEu phosphor. The inset shows the image of the phosphor in the daylight. Reproduced from Ref. [39] by permission of The Royal Society of Chemistry...

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