Infrared sensitive phosphors

Phosphors, infrared-sensitive, 3 11 strontium selenide-samarium-eu-ropium, 3 22... 

Use Nuclear-reactor control rods, especially in red-and infrared-sensitive phosphors. 

Phosphors. Infrared radiation can stimulate the emission of visible radiation from certain types of phosphors which have been previously excited by ultraviolet radiation. Becker and Risgin [2.71] have reported that self-activated ZnS crystals have exhibited both visible luminescence and photoconductivity when stimulated by radiation in the 1-3 pm interval. Geusic et al. [2.72] have shown that rare earth phosphors can convert very near infrared (0.93 pm) radiation into the visible with an efficiency as high as 1 %. Although phosphors can be employed to convert images directly, their lack of sensitivity has limited their usefulness. 

Spatial resolution due to thermal spread. Other two dimensional thermal sensors which have been considered include liquid crystals Ennulat and Fergason [3.72]), infrared sensitive phosphors (Urbach et al. [3.73]) and bolometric layers mounted in a camera tube to utilize electron beam readout. All these devices suffer primarily from poor spatial resolution, although their sensitivity was also rather low. 

Some of the procedures outlined below have been described previously. " They are designed for the preparation of phosphors that are to be used for quantitative studies of luminescence. Details are presented for the preparation of strontium nitrate, strontium chloride, strontium sulfate, and strontium selenite in a state of high purity for the reduction of the sulfate to the sulfide and the selenite to the selenide and for the conversion of the sulfide and the selenide into typical infrared-sensitive phosphors. 

Multicolored luminescence is the most attractive property of rare earth-based compounds. Lanthanide ions possess many sharp emission lines that cover the visible and near infrared (NIR) region due fo fhe abundanf fransifions of f-orbital configurations. However, the forbidden f-f fransi-fions induce narrow excitation lines for mosf rare earfh ions. This low absorbency cross-section is the bottleneck in practical application, so host-sensitized emission mode is commonly employed by rare earth phosphors. The vanadate matrix is one of fhe candidafes, which excifes lanthanide ions via charge-transfer energy migration. 

Samarium is used to dope calcium fluoride crystals for use in optical masers or lasers. Compounds of the metal act as sensitizers for phosphors excited in the infrared the oxide exhibits catalytic properties in the dehydration and dehydrogenation of ethyl alcohol. It is used in infrared absorbing glass and as a neutron absorber in nuclear reactors. The metal is priced at about 3.50/g (99.9%). Little is known of the toxicity of samarium therefore, it should be handled carefully. 

The fading of the information stored in the phosphor has to be slow (preferably the information must still be present several hours after exposure), e. Stimulation has to be possible in the red or near infrared. The stimulated emission has to be located between 300 and 500 nm where the photomultiplier tube has its highest sensitivity. 

Photographic plates are extremely sensitive photon detectors in this same region. The speed of data acquisition is, of course, much lower owing to the processing time required for the plate. Most photographic plates are insensitive in the infrared region, but infrared phosphors extend their range somewhat into the infrared. 

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