Ultraviolet Emitting Phosphor

Abstract

A calcium zinc phosphate phosphor activated with thallium has been developed for the generation of ultraviolet radiation and is especially rich in erythemal region. The peak of emission of this phosphor is dependent upon the ratio of the calcium to zinc. A phosphor in which 8 per cent of calcium is replaced by zinc in calcium phosphate has a peak emission at 3120 A, or very near that of maximum erythemal effectiveness.Forty‐watt fluorescent lamps made with this new phosphor in ultraviolet transmitting glass (9821) produced between 7.5 to 8.7 watts of ultraviolet radiations between 2800 A and 3800 Å with a peak emission at 3120 Å. The weighted erythemal effective radiation from this lamp is from 1300 to 1750 milliwatts, or about two and one half times the effective erythemal radiation from calcium phosphate activated with thallium.When it is considered that these lamps operate from an ordinary fluorescent ballast and are more efficient than any other source in producing erythemal radiations, a new avenue of approach is open for bringing the benefits of sunlight into schools, offices, and factories.