KR100366887B1 - Phosphor coating method for electroluminescence and phosphors manufactured accordingly - Google Patents

Abstract

Introducing an inert gas into the reaction vessel; Filling phosphor particles into a reaction vessel; Heating the reaction vessel to a 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. The present method yields a phosphor having a half life of at least 3,100 hours and an effect of at least 6 lumens / watt (lm / w).

Description

Electroluminescent Phosphor Coating Method And Phosphor Prepared According To

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

Coated 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. The coating method in some of the other of these patents uses chemical vapor deposition to apply a protective coating by hydrolysis. It would be an advance in the art if a coating method that could work without water or steam could be developed. Increasing the potency and lifetime of such coated phosphors would be a further advance.

Therefore, it is an object of the present invention to obviate the disadvantages of the prior art.

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

It is a further object of the present invention to provide a phosphor coating method which does not use water or water vapor.

These objects, in one aspect of the invention, the step of introducing an inert gas into the reaction vessel; Filling the phosphor particles into the reaction vessel, preferably with stirring; Heating the reaction vessel to a reaction temperature; Introducing a coating precursor into the reaction vessel; Introducing an oxygen / ozone mixture into the reaction vessel; Maintaining the inert gas flow, oxygen / ozone mixture flow and precursor supply for a time sufficient to coat the phosphor particles. This method produces phosphors with a conformal coating that substantially prevents moisture absorption and has a half-life of over 3100 hours while exhibiting effects over 6 lumens / watt (lm / w). This method is also accomplished in the absence of water or water vapor.

For a better understanding of the present invention, along with other and further objects, advantages, and capabilities, see 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 was charged to a 36 inch height reaction vessel. The shaft of the vibratory mixer was then operated at a rate of 60 cycles per minute and the reaction vessel was heated with an electric furnace that enclosed it. When the reaction vessel temperature reached 160 ° C., oxygen gas at a flow rate of 4.6 L / min was passed through the ozone generator at a rate sufficient to take 5-6 wt% ozone. The resulting ozone / oxygen mixture was 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 was passed through the vessel of the coating precursor maintained at room temperature. Preferred coating precursor is trimethylaluminum (TMA). Dilute TMA precursor vapor was introduced from the bottom of the reaction vessel and reacted with the ozone / oxygen mixture to form a protective, conformal coating on the surface of the individual phosphor particles. Coating time was 48 hours. The reaction vessel was maintained at 160 ± 3 ° C., and the nitrogen, precursor, and oxygen / ozone gas flow rates were all kept constant. The resulting coated phosphor had the properties shown as lot number 188D in Table 1. Half-life tests (indicated by lifetime (hours) in Table 1) are performed at 72 ° F., 50% relative humidity.

TABLE 1

Example 2

The procedure of Example 1 was followed except that the temperature was raised to 235 ° C. and the time was reduced to 40 hours. The resulting coated phosphor had the properties shown as lot number 189C in Table 1. While the potency increased from 6.7 lm / w to 7.6 lm / w, the half-life showed a slight decrease, but the half-life of 2300 hours still represents a usable commodity.

Other changes that occur in the phosphors baked at these different temperatures are reflected in the light output. Phosphors coated at 160 ° C. emit in the cyan area and phosphors coated at 235 ° C. move toward yellow.

Further testing confirmed that the results could be better by increasing the reaction time up to about 70 hours and increasing the temperature for the cyan emitting material to about 180 ° C. As can be clearly seen from Table 1, there are two optimum temperatures in the method for providing long-lived and efficient phosphors with one of two color points.

Longer reaction times are expected to be more effective, but of course the reaction time should be dependent on the size and / or quantity of the reaction vessel and the amount of production desired or needed for the commodity at the appropriate price.

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)

Introducing an inert gas into the reaction vessel; Filling phosphor particles into a reaction vessel; Heating the reaction vessel to a reaction temperature; Introducing a coating precursor into the reaction vessel; Introducing an oxygen / ozone mixture into the reaction vessel; Maintaining the inert gas flow, oxygen / ozone mixture flow and 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 for coating phosphor particles according to claim 1, wherein the reaction temperature is 160 ° C. The method of claim 1, wherein the reaction temperature is 160 ℃ to 180 ℃ coating method. The method for coating phosphor particles according to claim 1, wherein the reaction temperature is 235 ° C. The method of claim 1, wherein a time sufficient to coat the phosphor particles is 40 to 70 hours. An electroluminescent phosphor prepared according to any one of claims 1 to 8, having a conformal moisture absorption inhibiting coating and having a half-life greater than 2,000 hours. An electroluminescent phosphor prepared according to any one of claims 1 to 8, having a conformal moisture absorption inhibiting coating and having a half-life greater than 3,000 hours. The method of claim 1, wherein the phosphor particles are agitated at the filling of the phosphor particles into the reaction vessel. 12. The method of claim 11, wherein said agitation is maintained during introduction of the oxygen / ozone mixture. A coated phosphor produced according to the method of claim 1. A coated electroluminescent phosphor produced according to the method of claim 1. Coated particles produced according to the method of claim 1.