Method for effectively contacting manganese-activated zinc silicate phosphor with antimony oxide during phosphor coating, and resulting lamp

A fluorescent lamp having a predetermined correlated color temperature and combined high efficacy and good color rendition, said lamp comprising a sealed elongated light-transmitting envelope having electrodes operatively positioned therein proximate the ends thereof and enclosing a discharge-sustaining filling comprising mercury and a small charge of inert ionizable starting gas which when energized generates a discharge comprising ultraviolet radiations and a limited proportion of visible radiations, phosphor means comprising a predetermined amount of a first phosphor layer carried on the inner surface of said envelope, a predetermined amount of a second phosphor layer coated on and carried on said first phosphor layer, and a predetermined amount of a third phosphor layer coated on and carried on said second phosphor layer so that said third phosphor layer is positioned nearest to said discharge;

• said first phosphor layer principally comprising finely divided apatite-structured calcium halophosphate activated by predetermined proportions of antimony and manganese, said first phosphor layer when excited by said discharge emitting visible radiations of a color which approximates said predetermined correlated color temperature of said lamp, said first phosphor layer having been applied in predetermined amount by flowing over the envelope interior surface a phosphor coating paint comprising a liquid vehicle and organic binder having said first phosphor suspended therein as a slurry, said coating paint also including a small predetermined amount of finely divided antimony oxide, and said applied coating paint having been lehred at a temperature sufficient to volatilize the organic binder therefrom but insufficient to volatilize more than a minor proportion of said antimony oxide;
• and
• said second phosphor layer substantially comprising a mixture of predetermined amounts and relative proportions of finely divided narrow-band blue-emitting phosphor activated by divalent europium and having an emission substantially confined to the wavelength range of from 430 nm to 485 nm, finely divided green-emitting manganese-activated zinc silicate, and finely divided red-orange-emitting trivalent-europium-activated yttrium oxide, the predetermined amounts and relative proportions of said mixed phosphors comprising said second phosphor layer when excited by said discharge emitting visible radiations of a color which approximates said predetermined correlated color temperature of said lamp, said second phosphor layer having been applied in predetermined amount by flowing over said lehred first phosphor layer a second phosphor coating paint comprising a liquid vehicle and organic binder having said phosphors of said second layer mixed and suspended therein as a slurry, and said second layer applied coating paint having been lehred at a temperature sufficient to drive organic binder therefrom and also sufficient to volatilize an appreciable portion of residual antimony oxide in said first phosphor layer to cause said volatilized antimony oxide to contact said manganese-activated zinc silicate;
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• said third phosphor layer substantially comprising a mixture of predetermined amounts and relative proportions of finely divided narrow-band blue-emitting phosphor activated by divalent europium and having an emission substantially confined to the wavelength range of from 430 nm to 485 nm, finely divided green-emitting magnesium aluminate activated by cerium and terbium, and finely divided red-orange-emitting trivalent-europium-activated yttrium oxide, and the predetermined amounts and relative proportions of said mixed phosphors comprising said third layer when excited by said discharge emitting visible radiations of a color which approximates said predetermined correlated color temperature of said lamp.

The method of effectively exposing manganese-activated zinc silicate phosphor to antimony oxide in order to improve the performance of said zinc silicate phosphor when it is included as a part of a multiple layer phosphor coating on the interior surface of an elongated envelope for a fluorescent lamp, which method comprises:

• in the lamp manufacturing process, flowing over the envelope interior surface a first phosphor means coating paint comprising a liquid vehicle and organic binder having a first phosphor means suspended therein as a slurry, and said coating paint also including a small predetermined amount of finely divided antimony oxide, and lehring said envelope and applied coating paint at a temperature sufficient to volatilize the organic binder therefrom but insufficient to volatilize more than a minor proportion of said antimony oxide;
• flowing over said lehred first phosphor means layer a second phosphor means coating paint comprising a liquid vehicle and organic binder having a second phosphor means which includes said manganese-activated zinc silicate suspended therein as a slurry, and lehring said envelope and applied second coating paint at a temperature sufficient to volatilize the organic binder therefrom and also sufficient to volatilize and appreciable portion of residual antimony oxide in said first-applied phosphor means layer to cause said volatilized antimony oxide to contact said manganese-activated zinc silicate.