KR19990037377A - Method of manufacturing long life electroluminescent fluorescent material - Google Patents

Abstract

Introducing an inert gas into the reaction vessel; Filling the reaction vessel with fluorescent particles; Heating the reaction vessel to the reaction temperature; Introducing a coating precursor into the reaction vessel; Introducing an oxygen / ozone mixture into the reaction vessel; Maintaining the stirring, inert gas flow, oxygen / ozone mixture flow and precursor feed for a time sufficient to coat the phosphor particles. This method yields a fluorescent material having a half life of at least 3,100 hours and an effect of at least 6 lumens / watt (lm / w).

Description

Method of manufacturing long life electroluminescent fluorescent material

The present invention relates to coated particles, more particularly to particles having conformal coatings. More particularly, the present invention relates to electroluminescent phosphors having a coating which, in particular, prevents moisture absorption of the phosphor and significantly increases its lifetime and potency.

Coating phosphors are known from US Pat. Nos. 4,585,673, 4,828,124, 5,080,928, 5,118,529, 5,156,885, 5,220,243, 5,244,750, and 5,418,062. It is known from some of the above patents that coating precursors and oxygen can be used to apply the protective coating. See, for example, US Pat. Nos. 5,244,750 and 4,585,673. Coating methods of several of these patents use chemical vapor deposition to apply protective coatings by hydrolysis. Technological advances will be made if coating methods can be developed that work in the absence of water or water vapor. The development of this method will be a further advance to increase the potency and lifetime of these coated phosphors.

It is therefore an object of the present invention to obviate the disadvantages of the prior art.

It is a further object of the present invention to enhance the operation of the coated phosphor.

A further object of the present invention is to provide a method for coating a fluorescent substance without using water or water vapor.

These objects, in one aspect of the invention, introduce an inert gas into the reaction vessel; The phosphor particles are preferably filled into the reaction vessel with stirring; Heating the reaction vessel to the reaction temperature; Introducing a coating precursor into the reaction vessel; Introducing an oxygen / ozone mixture into the reaction vessel; It is achieved by a method for coating a phosphor particle comprising maintaining an inert gas flow, an oxygen / ozone mixture flow and a precursor feed for a time sufficient to coat the phosphor particles. This method produces conformal coated phosphors that substantially eliminate moisture absorption and provide phosphors having a half-life of at least 3100 hours with an effect of at least 6 lumens / watt (lm / w). This method is also accomplished in the absence of water or water vapor.

To better understand the present invention, along with other and further objects, advantages, and capabilities thereof, reference is made to the following description and claims.

Example 1

Inert gas, preferably nitrogen, is introduced at the bottom of the hollow 2 inch diameter quartz reaction vessel used as the fluidized bed reactor at a flow rate of 4.5 l / min. 2.5 kg of copper-doped zinc sulfide electroluminescent phosphor is charged into a 36 inch high reaction vessel. The shaft of the vibrating mixer is then operated at a rate of 60 cycles per minute and the reaction vessel is heated with an electric furnace enclosing it. When the reaction temperature reaches 160 ° C., oxygen gas at a flow rate of 4.6 L / min is passed through the ozone generator at a rate sufficient to take 5 to 6 wt% ozone. The ozone / oxygen mixture is fed into the reaction vessel through the opening of the hollow vibrating shaft. In addition, nitrogen gas at a flow rate of 0.5 l / min is passed through a container of coating precursor maintained at room temperature. Preferred coating precursor is trimethylaluminum (TMA). Dilute TMA precursor vapor is introduced from the bottom of the reactor vessel to react with the ozone / oxygen mixture to form a protective conformal coating on the individual phosphor particle surfaces. Coating time is 48 hours. The reaction vessel is maintained at 160 ± 3 ° C and the nitrogen, precursor and oxygen / ozone gas flow rates are all kept constant. The resulting coated phosphor has the properties shown in lot number 188D in Table 1. Half-life tests (labeled Life Hrs in Table 1) are performed at 72 ° F., 50% relative humidity.

Lot number Temperature (℃) Hour TMA / N ₂ (ℓ / min) O ₂ O ₃ (ℓ / min) N ₂ (ℓ / min) BET (m ² / gm) aluminum(%) Lamp performance Light output Life time (hours) Effect (lm / w) 24 hours 100 hours 188D 160 48 0.5 4.6 4.5 0.05 4.1 19.3 19.6 3,156 6.7 189C 235 40 0.5 4.6 4.5 0.08 4.2 19.5 18.6 2,302 7.6

Example 2

The procedure of Example 1 was followed except that the temperature was raised to 235 ° C. and the time was limited to 40 hours. The resulting coating phosphor has the properties shown in lot number 189C in Table 1. While the effect increases from 6.7 lm / w to 7.6 lm / w, the half-life shows a slight decrease, but the 2300-hour half-life still represents a usable commodity.

Other changes that occur in phosphors that glow at different temperatures are reflected in the color output. The fluorescent material coated at 160 ° C. emits in the cyan region and the fluorescent material coated at 235 ° C. moves toward yellow.

Further tests show that the results are further improved by increasing the reaction time to about 70 hours and increasing the temperature for the cyan emitting material to about 180 ° C. As will be clear from Table 1, there are two optimal firing temperatures to provide the method with one of two color points and a long lifetime of efficient phosphor.

Longer reaction times are also expected to be more effective, but of course must depend on the size and / or quantity of the reaction vessel and the throughput required or required for the production of a viable titer.

While what is presently considered to be a preferred embodiment of the invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications can be made herein without departing from the scope of the invention as defined by the claims. will be.

Claims (15)

A coating method of fluorescent substance particles, comprising: introducing an inert gas into a reaction vessel; Filling the reaction vessel with fluorescent particles; Heating the reaction vessel to the reaction temperature; Introducing a coating precursor into the reaction vessel; Introducing an oxygen / ozone mixture into the reaction vessel; Maintaining the inert gas flow, the oxygen / ozone mixture flow, and the precursor supply for a time sufficient to coat the phosphor particles. The method of claim 1 wherein the precursor is trimethylaluminum. The method of claim 1 wherein the oxygen / ozone mixture comprises about 5 to 6 weight percent ozone. The method of claim 1 wherein the inert gas is nitrogen. The method of claim 1 wherein the reaction temperature is about 160 ° C. 3. The process of claim 1 wherein the reaction temperature is 160 to 180 ° C. The method of claim 1 wherein the reaction temperature is about 235 ° C. 3. The method of claim 1 wherein the time sufficient to coat the phosphor is from about 40 to about 70 hours. An electroluminescent phosphor having a conformal moisture absorption inhibiting coating and a half life of at least 2,000 hours. The electroluminescent phosphor of claim 9, wherein the half life is at least 3,000 hours. The method of claim 1 wherein the phosphor particles are filled into the reaction vessel with stirring. The method of claim 11, wherein stirring is maintained during the introduction of the oxygen / ozone mixture. A coating phosphor produced according to the method of claim 1. A coated electroluminescent phosphor produced according to the method of claim 1. Coating particles produced according to the method of claim 1.