Luminescent materials

Details Luminescent materials Luminescent materials

2000-08-29

2002-05-14

Koslow, C. Melissa (Department: 1755)

Compositions

Inorganic luminescent compositions

Compositions containing halogen; e.g., halides and oxyhalides

C252S30140R

Reexamination Certificate

active

06387298

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel oxide-based phosphorescent material that emits orange light, and more particularly to a novel phosphorescent material produced from CaO and Ti.
The phosphorescent material which emits orange light of the present invention has a number of advantages as a phosphorescent material, namely, being produced easily, being chemically stable, and being highly safe.
2. Description of the Related Art
Clock dials, instrument display panels of various kinds, guide signs, and the like having light-emitting capabilities are used widely at night or in emergency situations, as well as in ordinary businesses to call the attention of workers. In the past, luminous paints containing radioactive elements were widely used for these purpose, but radiation exposure injuries were a concern, so currently a number of different luminescent and phosphorescent materials are used. Specific examples are CaS:Bi (purple-blue), CaSrS: Bi (SrS 10-20%) (blue), ZnS:Cu (yellow-green) ZnCdS:Cu (CdS 5-10%) (yellow), and ZnCdS:Cu (CdS 20-30%) (orange) and the like; however, these compounds, being sulfides, have poor chemical stability in air. Of the preceding compounds, those emitting yellow or orange light all contain cadmium, an extremely toxic element. Accordingly, the current trend is to avoid using phosphorescent materials that emit yellow or orange light.
Functional and design requirements for clock dials, instrument display panels of various kinds, guide signs, and the like have become more diverse recently. Thus, the absence of any suitable yellow or orange light-emitting phosphorescent materials represents a significant limitation, and there is an urgent need for new phosphorescent materials.
It is an objective of the present invention to meet this need by providing a novel orange light-emitting phosphorescent material.
As a result of extensive diligent research aimed at development of a novel phosphorescent material, conducted in view of the conventional art, the inventors have discovered that emission of orange phosphorescence can be achieved simply by adding Ti to CaO, and that this phenomenon can be employed to produce a novel phosphorescent material, and, therewith, have accomplished the present invention.
SUMMARY OF THE INVENTION
The present invention provides a novel phosphorescent material emitting orange light that is highly safe due to no toxicity, and chemically stable in air.
The present invention relates to a novel phosphorescent material obtained by adding Ti to CaO, that is Ti—CaO phosphorescent material, produced from a starting material of calcium oxide (CaO), or of calcium carbonate (CaCO
3
), calcium hydroxide(Ca(OH)
2
), calcium sulfate(CaSO
4
), calcium oxalate (CaC
2
O
4
), or other compound to be converted to CaO through heating in air, by a process of bringing this starting material into contact with metallic titanium (Ti) and conducting heat treatment thereof in vacuo or in an atmosphere that is not reactive with Ti such as argon gas and the like, or by a process of mechanical alloying and the like of CaO and Ti.
The present invention employs the following technical means to solve the aforementioned problem.
(1) A phosphorescent material emitting orange light, which comprises as essential components the three elements of calcium (Ca), oxygen (O), and titanium (Ti)
(2) The phosphorescent material according to above (1), wherein the material is obtained by adding Ti to calcium oxide (CaO).
(3) The phosphorescent material according to above (2), wherein the material is obtained by adding Ti as an interstitial element into the CaO crystal lattice.
(4) The phosphorescent material according to above (2), wherein the material is obtained by adding Ti to a starting material of calcium carbonate (CaCO
3
), calcium hydroxide(Ca(OH)
2
), calcium sulfate(CaSO
4
), calcium oxalate (CaC
2
O
4
), or other compound to be converted to CaO through heating in air.
(5) The phosphorescent material according to above (3), wherein the material is obtained by adding Ti to a starting material of calcium carbonate (CaCO
3
), calcium hydroxide(Ca(OH)
2
), calcium sulfate(CaSO
4
), calcium oxalate (CaC
2
O
4
), or other compound to be converted to CaO through heating in air.
The phosphorescent material of the present invention is produced from a starting material of calcium oxide (CaO), or of calcium carbonate (CaCO
3
), calcium hydroxide(Ca(OH)
2
), calcium sulfate(CaSO
4
), calcium oxalate (CaC
2
O
4
), or other compound to be converted to CaO through heating in air, by a process of bringing this starting material into contact with metallic titanium (Ti) and conducting heat treatment thereof in vacuo or in an atmosphere that is not reactive with Ti such as argon gas, or by a process of mechanical alloying and the like of CaO and Ti.
The present invention will be now described in greater detail.
The present invention is a novel phosphorescent material emitting orange light comprises calcium oxide (CaO) and Ti containing as essential components the three elements of calcium (Ca), oxygen (O), and titanium.
The CaO may be a dense or porous sinter and the like produced by fine ceramics fabrication techniques such as pressure sintering e.g., hot pressing or normal pressure sintering and the like, or it may be a powder. As the compounds to be converted to CaO through heating in air, for example, CaCO
3
, Ca(OH)
2
, CaSO
4
, or CaC
2
O
4
, either alone or in combination, may be used in the form of sinter or powder or the like in place of CaO.
With respect to the metallic Ti in various forms, bulk form, e.g., sheet, foil, wire, etc. of various types, containers fabricated therefrom, e.g., a plate, board, crucible, etc., powders of various particle sizes, or thin films produced by techniques such as sputtering, may be used as the Ti. In preferred practice, substantially pure Ti is used preferably. The reason thereof is that in case of Ti alloys such as Ti—6Al—4V and the like, the alloy elements affect a specific quality of oxide film to be formed on the Ti surface, and diffusion of these alloy elements per se into the CaO competes with Ti diffusion, resulting in a drop in production efficiency relative to pure Ti when used to produce the phosphorescent material of the invention. Accordingly, while high purity is not always necessary, it is preferable to use industrial grade Ti as per JIS, specifically, Ti having JIS Grade 3 purity or higher.
The CaO—Ti phosphorescent material may be produced using, for example, a CaO sinter by bringing a sheet, wire, powder or the like of metallic Ti into contact therewith, or forming a Ti film through a technique such as deposition or sputtering, and then holding in vacuo or in an atmosphere that is not reactive with Ti such as argon gas, at a temperature of 1000° C.-1660° C. and preferably 1350° C. Where the holding temperature is above 1660° C., the Ti will melt, and this will make it difficult to separate the CaO and Ti after processing, as well as causing excessive reaction of CaO and Ti so that a CaO.TiO
2
complex oxide forms, resulting in failure to obtain a phosphorescent material. Where the holding temperature is below 1000°C., CaO and Ti do not react sufficiently, resulting in failure to obtain a phosphorescent material.
Where a CaO powder is used, the CaO—Ti phosphorescent material may be produced by processing in the same manner as with the CaO sinter, or by placing the powder in a metallic Ti crucible, board, or similar container, and, in the same manner as with the CaO sinter, holding in vacuo or in an atmosphere that is not reactive with Ti such as argon gas, at a temperature of 1000° C.-1660° C., and preferably 1350° C., to obtain a phosphorescent material. Alternatively, rather than employing a heat treatment like those described above, the phosphorescent material can be produced by subjecting the CaO powder and metallic Ti of some form to mechanical alloying or similar technique.
Alternatively, a CaO powder or powder compact can be stacked with a metallic Ti sheet or foi

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