JPH0662946B2 - Slow electron beam excited phosphor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a phosphor that emits light with high brightness under excitation by a slow electron beam.

(Prior Art) Conventionally, a zinc-activated zinc oxide phosphor (ZnO: Zn) is well known as a phosphor that emits light with high brightness when excited by a low-speed electron beam having an accelerating voltage of 1 kV or less, particularly 100 V or less. There is. This ZnO: Zn phosphor exhibits high-intensity green-white emission when excited by a low-speed electron beam, and is practically used as a fluorescent film of a low-speed electron beam-excited fluorescent display tube.

A low-speed electron beam excitation fluorescent display tube (hereinafter abbreviated as "fluorescent display tube") basically has an anode plate having a fluorescent film on one surface, and a cathode provided so as to face the fluorescent film. To
The inside of the container is sealed in a vacuum, and the low-speed electron beam emitted from the cathode (generally the acceleration voltage is 100 V
The following low-speed electron beam) excites the fluorescent film on the anode plate to emit light. The fluorescent display tube having a fluorescent film made of the above ZnO: Zn fluorescent material is a desk calculator,
It is widely used as a display device for various measuring instruments.

In recent years, as the field of use of fluorescent display tubes has expanded, it has become desirable to diversify the emission color of fluorescent display tubes, and the development of fluorescent materials that emit light other than green under the excitation of low-speed electron beams has become active. Has been advanced to. As a result, some phosphors that emit light other than green under slow electron beam excitation were found. One of them had a composition formula of (Zn _1-x , Cd _x ) S: Ag. The fluorescent substance represented by is taken as an example (Zn _1-x , Cd _x ).
There are S-type fluorescent materials.

In manufacturing such a (Zn _1-x , Cd _x ) S-based phosphor, HW Leverenz, “An Introduction To Luminesce
nce Of Solids, pp. 196-199, John Wiley & Sons, I
nc., 1950, JP-A-55-129480 and JP-A-57-167381.
It is known in the art to use NaCl as disclosed in US Pat.

Further, for example, as a means for increasing the brightness of a fluorescent display tube using the above (Zn _1-x , Cd _x ) S: Ag phosphor, increasing the Ag content of the phosphor is preferable. JP-A-57
No. 167381, on the other hand, in Japanese Patent Publication No. 59-33153, etc., in order to achieve this object, a conductive substance such as In ₂ O ₃ having a small particle size and a phosphor are mixed. Is disclosed.

However, with the colorization of fluorescent display tubes and the expansion of their fields of use, it has been demanded to further increase the brightness of light emission of fluorescent display tubes under low-voltage electron beam excitation, that is, at low voltage and low power. There is.

(Object of the Invention) In view of the above-mentioned demand, the present invention has an accelerating voltage of 1 kV or less, particularly 10 kV.
It is an object of the present invention to provide a phosphor that emits light with high brightness under the excitation of a low-speed electron beam of 0 V or less.

(Structure of the Invention) In order to achieve the above object, the present inventors have developed a phosphor that emits light under low-speed electron beam excitation (hereinafter referred to as “low-speed electron beam-excited phosphor”).
The above (Zn _1-x , Cd _x ) S-based phosphors have been earnestly studied, and as a result, lithium (Li)
The (Zn _1-x , Cd _x ) S-based phosphor containing Si exhibits only light emission with a brightness equal to or lower than that of a conventional (Li-free) phosphor under high-speed electron beam excitation. Nevertheless, they found that their emission under slow electron beam excitation was much higher than that of the conventional one, and completed the present invention. This finding is considered to be extremely important in showing that the addition of lithium imparts a fundamentally different characteristic from the conventional one.

The slow electron beam excited phosphor of the present invention based on such a discovery is represented by the general formula (Zn _1-x , Cd _x ) S: aLi, bM ^I , cX (where 0 ≦ x ≦ 1,0 <a <1 × 10 ^-2 g / g, b>
0, c> 0, M ^I is at least one element in Ag and Au, and X is Al, Cl, Br and I.
Is at least one element of ), And is a (Zn _1-x , Cd _x ) S-based phosphor containing Li.

It has been found that in the phosphor of the present invention, even if the content of Li is a minute amount (1 ppm or less) which is about the detection limit in the current analytical technique, the desired improvement in brightness can be obtained. The type of lithium salt used and the number of combinations can be arbitrarily adjusted. Moreover, the upper limit of the Li content was determined to be 10 ^-2 g / g (10000 ppm) from the current manufacturing technology.

Li has a content of 1 ppm to 7100 p with respect to the phosphor matrix.
It is preferably in the range of pm and more preferably in the range of 35 ppm to 5000 ppm.

The phosphor of the present invention is generally produced by the method described below. That is, zinc sulfide (ZnS) powder and cadmium sulfide (CdS) powder were mixed with Zn based on x mol of CdS powder.
For example, AgCl, HAuCl ₄ or the like can be added to the mixed sulfide powder formed by mixing the S powder in a ratio such that the S powder is (1-x) mol.
At least one compound of Ag and Au which is an activator and a compound containing an element (X) which is a co-activator such as Al (NO ₃ ) ₃ and NaCl are added and mixed in a predetermined amount, and further, As a lithium supply source, not only Li simple substance but also an appropriate amount of any kind and number of lithium salts such as lithium halides such as lithium chloride, lithium sulfate, lithium phosphate, oxyacid salts, etc. are added, and hydrogen sulfide atmosphere, sulfur It can be obtained by baking in a sulfidizing atmosphere such as an atmosphere at 500 to 1200 ° C. for 0.2 to 5 hours, thoroughly washing with a solvent such as water, dehydration and drying. At this time, at least one alkali metal halide of Na, K, Rb and Cs may be added as a flux to the phosphor raw material and baked.

FIG. 1 shows an example of the slow electron beam excited phosphor of the present invention thus obtained (Zn _0.65 , Cd _0.35 ) S: Li, A
7 is a graph showing the relationship between the Li content of the phosphor and the characteristic value in a fluorescent display tube having a phosphor film using a g, Cl phosphor.

In the drawing, curves a ₁ , b ₁ and c ₁ correspond to the above-mentioned phosphor produced by adding LiCl as a lithium salt, and curves a ₂ , b ₂ and c ₂ are lithium salts in an equimolar amount.
Cl, Li ₂ SO ₄ .H ₂ O and Is added to the mixture, and an equimolar amount of N is added to these lithium salts.
It corresponds to the above-mentioned phosphor produced by adding aCl. The curves a ₁ and a ₂ are the light emission start voltage (that is, 0.1 cd / m 2
² shows the change in the applied voltage required to obtain a luminance of ² ) depending on the Li content, while the curves b ₁ and b ₂ show the changes in the Li content when the applied voltage is 50 V (under the slow electron beam excitation). The luminance change and curves c ₁ and c ₂ respectively show the luminance change depending on the Li content when the applied voltage is 12 kV (under high-speed electron beam excitation). In addition, the value represented as Li content 0 in each curve in the present drawing is a value measured for a fluorescent display tube obtained by using a conventional phosphor containing no Li. As shown in this drawing, it was confirmed that the addition of Li to the phosphor resulted in a decrease in the light emission starting voltage and a marked improvement in the light emission luminance under the low-speed electron beam excitation.

(Effect of the invention) As described above, the slow electron beam excited phosphor of the present invention is (Zn
By adding Li to the _1-x , Cd _x ) S-based phosphor, a remarkably high emission brightness is exhibited under an accelerating voltage of 1 kV or less, particularly 100 V or less under low-speed electron beam excitation. It is useful for a fluorescent display tube as a light-emitting composition composed of a mixture of a metal oxide and a conductive substance, and its industrial utility value is extremely large.

(Example) Next, the present invention will be described with reference to an example.

Example 1 Zinc sulfide (ZnS) reagent fluorescent grade product 137.5 g Cadmium sulfide (CdS) reagent fluorescent grade product 87.5 g CdS containing 2000 ppm of silver 25 g Lithium chloride (LiCl) reagent special grade 2.5 g was mixed well, 80 in an electric furnace in a quartz crucible
After baking at 0 ° C. for 2 hours and sieving with water, the supernatant is washed with water until it has a conductivity of 3 μs / cm, dehydrated and dried to give a Li content of (Zn _0.65 , Cd _0.35 )
S: 6.5 ppm with respect to Ag and Cl 1 g (Zn _0.65 ,
A Cd _0.35 ) S: Li, Ag, Cl phosphor was obtained.

This fluorophore is mixed in a binder consisting of ethyl cellulose and carbitol to form an ink, which is applied on a plate using a 250-mesh silk screen and then at 450 ° C. for 3 days.
Heat for 0 minutes and dry at 100 ° C for 30 minutes (Z
A fluorescent film made of n _0.65 , Cd _0.35 ) S: Li, Ag, Cl phosphor was formed.

On the other hand, apart from this, the conventional (Z
n _0.65 , Cd _0.35 ) S: Ag, Cl phosphor is obtained, and (Zn _0.65 , Cd _0.35 ) S: A is obtained in the same manner as in the preparation of the fluorescent film.
A fluorescent film composed of a g, Cl fluorescent substance was formed.

Each of the fluorescent films obtained as described above was placed in a vacuum vessel and excited by a slow electron beam of 50 V (Zn _0.65 , Cd
_The fluorescent film made of _0.35 ) S: Li, Ag, Cl phosphor showed about 30 times the relative light emission luminance of the fluorescent film made of (Zn _0.65 , Cd _0.35 ) S: Ag, Cl phosphor.

Example 2 Equimolar amounts of LiCl and Li ₂ SO ₄ .H in the phosphor raw material
_{With 2} O Conventional (Zn _0.9 , Cd _0.1 ) except for adding and firing
Similar to the S: Au, Al phosphor, the Li content is (Z
n _0.9 , Cd _0.1 ) S: 1000 ppm with respect to Au and Al 1 g
To obtain a (Zn _0.9 , Cd _0.1 ) S: Li, Au, Al phosphor. On the other hand, for comparison, a conventional (Zn _0.9 , Cd _0.1 ) S: Au, Al phosphor containing no Li was obtained. Using these phosphors, a fluorescent film was formed in the same manner as in Example 1, placed in a vacuum container, and excited with a slow electron beam of 50 V (Zn _0.9 , Cd _0.1 ) S: Li, Au, The fluorescent film made of an Al phosphor is (Zn _0.9 , Cd _0.1 ) S: Au, Al.
The emission brightness was 3.5 times that of a fluorescent film made of a fluorescent substance.

Example 3 Equimolar amounts of LiCl and Li ₂ SO ₄ .H in the phosphor raw material
_{With 2} O And the conventional (Zn
_0.7 , Cd _0.3 ) S: Ag, Al Similar to the phosphor, L
The i content is 400 ppm with respect to (Zn _0.7 , Cd _0.3 ) S: Ag, Al 1 g, and the Na content is 7 ppm (Zn _{0.7
A 0.7} , Cd _0.3 ) S: Li, Na, Ag, Al phosphor was obtained. On the other hand, for comparison, the conventional (Zn
_0.7 , Cd _0.3 ) S: Ag, Al phosphor was obtained. Using these phosphors, a fluorescent film was formed in the same manner as in Example 1, placed in a vacuum container, and excited with a slow electron beam of 50 V (Zn _0.7 , Cd _0.3 ) S: Li, Ag, The fluorescent film made of the Al phosphor showed (Zn _0.7 , Cd _0.3 ) S: Ag, four times the emission luminance of the fluorescent film made of the Al phosphor.

Example 4 ZnS: Li, Ag, Al phosphor having a Li content of 300 ppm in the same manner as the conventional ZnS: Ag, Al phosphor except that LiCl is added to the phosphor raw material and fired. Got On the other hand, for comparison, conventional Zn containing no Li
An S: Ag, Al phosphor was obtained. Using these phosphors, a fluorescent film was formed in the same manner as in Example 1, placed in a vacuum container, and excited with a low-velocity electron beam of 50 V, ZnS: Li, A
The fluorescent film composed of the g, Al phosphor showed twice the emission luminance as that of the fluorescent film composed of the ZnS: Ag, Al phosphor.

[Brief description of drawings]

FIG. 1 shows an example of a slow-electron-beam-excited phosphor of the present invention (Zn _0.65 , Cd _0.35 ) S: Li, Ag, Cl, which is used in a fluorescent display tube having a fluorescent film. It is a graph which shows the relationship between the content of Li in the phosphor and the changes in the emission luminance and the emission start voltage.

Claims (2)

[Claims] 1. A general formula (Zn _1-x , Cd _x ) S: aLi, bM ^I , cX (wherein 0 ≦ x ≦ 1,0 <a <1 × 10 ⁻² g / g, b>)
0, c> 0, M ^I is at least one element in Ag and Au, and X is A, C, Br and I.
Which is at least one element in the above). 2. In the above general formula, M ^I is Ag, X
Is C. The slow electron beam excited phosphor according to claim 1, wherein