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Phosphors

IP.com Disclosure Number: IPCOM000060848D
Original Publication Date: 1986-May-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 15K

Publishing Venue

IBM

Related People

Takamori, T: AUTHOR

Abstract

A group of phosphors is described herein which consist of single- crystal particles in which more than one activator is incorporated in different layers of the same crystal particle, forming a so-called "onion-skin" structure. These phosphors are useful for beam-penetration color CRTs, particularly for small projection systems where improved resolution as well as high light emission is required. The fine and well-crystallized phosphors described below meet these requirements. A method for making such phosphors is also set forth. Previously, phosphors with onion-skin structure were prepared by coating small phosphor particles on large-core phosphor particles. Obviously, such a process has various problems in itself.

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Phosphors

A group of phosphors is described herein which consist of single- crystal particles in which more than one activator is incorporated in different layers of the same crystal particle, forming a so-called "onion-skin" structure. These phosphors are useful for beam-penetration color CRTs, particularly for small projection systems where improved resolution as well as high light emission is required. The fine and well-crystallized phosphors described below meet these requirements. A method for making such phosphors is also set forth. Previously, phosphors with onion-skin structure were prepared by coating small phosphor particles on large-core phosphor particles. Obviously, such a process has various problems in itself. For example, the surface coverage of the core particles needs an extensive trial- and-error adjustment for optimization. The small phosphor particles cannot be appreciably smaller than a micron or so to avoid significant loss of their efficiency. Since the penetration depth of an electron beam into the phosphor particles on the CRT screen is known to be a micron or two, the particles cannot be much larger either. The uniformity of the coating is also questionable in many cases. Another method of preparing the onion-skin phosphors has also been proposed. In this method, the activator in the outer skin of the core phosphor particles is changed chemically, such as by oxidation or reduction, to attain luminescence properties in the outer skin different from that of the core. An example is the use of the divalent and trivalent europium ions as activators for green and red, respectively, in a strontium aluminate host. However, it is not easy to find a host structure which will be efficiently activated by ions of both valency states. In the present process the outer skin of the phosphor layer is grown over the core crystal phosphors under hydrothermal conditions to attain the onion-skin structure. Particles of the resultant phosphors are, therefore, fine single crystals with a voltage-dependent color variation. The advantage of such phosphors over conventional onion- skin phosphors for CRT applications is obvious. The size of the single particle of the phosphor can be much smaller than that of the latter for better resolution, and their better crystallinity, as grown single crystals, will carry greater resistance against degradation in high beam intensity applications such as in projection systems. The uniform size of the coating allows better control of the color-beam relationship as well. A method of preparing well-crystallized, fine and near mono- sized powders by hydrothermal processing with controlled nucleation density has been described elsewhere. Subsequent experimentation on YAG:Tb systems clearly supported its feasibility, and the effect of seeding on the growth of fine, well-isolated crystals in the hydrothermal system has been es...