New Ultraviolet Phosphors

Ultraviolet phosphors are defined as materials emitting fluorescent radiation of predominantly shorter wave lengths than visible light. Older phosphors of this type are reviewed briefly and three newly developed calcium phosphate phosphors are discussed in detail. Composition and method of preparation of cerium 3+ activated 360 BL phosphor are outlined, and an analysis of its structure is presented. The brightest phosphors contain about 10% of activator and are of γ tri‐orthophosphate structure. The significance of steam‐hydrogen firing is pointed out. The phosphor has a sensitivity of about 80% of maximum at λ 2,537. Its spectral energy distribution curve is of characteristic shape with a peak near 3,600 Å and with a tail extending into the blue region of the spectrum. A number of practical applications are listed. Further incorporation of small percentages of thorium causes an additional brightness gain of the order of 10% or more, without substantial shift of peak. Several possible reasons for this are given. Thallium‐activated calcium phosphate shows an emission curve of normal shape lying entirely in the ultraviolet with a peak at 3,250 Å. It is of β tri‐orthophosphate structure. Its sensitivity to λ 2,537 is very near maximum. Its usefulness for application in fluorescent sun lamps is pointed out. Methods of measuring and appraising ultraviolet phosphors are discussed. Fluorescent sun lamps have been made in the 40 watt T 12 size with outputs as high as 12,000 E vitons/steradian.