JPS6146028B2 - - Google Patents

Abstract

PURPOSE:A luminescent composition emitting red light with high luminance with a low-speed electron beam excitation, which is prepd. by mixing a silver- activated zinc cadmium sulfide fluorescent material with indium oxide. CONSTITUTION:A luminescent composition prepd. by mixing a silver-activated zinc cadmium sulfide fluorescent material, (Zn1-x, Cdx)S:AG, composed of a mother substance consisting of zinc cadmium sulfide, (Zn1-x, Cdx)S (wherein 0.65<=x<=1.0), and contg. as an activator 2X10<-4>-10<-2>g silver per g of said mother substance with indium oxide in a wt. ratio of 7:3-99:1. Said Ag-activated zinc cadmium sulfide fluorescent material which is more highly activated with Ag than the conventional one is enhanced in luminance by baking according to screen printing, and further markedly enhanced by adding an adequate amt. of In2O3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a luminescent composition that exhibits high-intensity red light emission under slow electron beam excitation.

Conventionally, zinc-activated zinc oxide phosphor (ZnO:Zn) is well known as a phosphor that emits light with high volatility when excited by a slow electron beam with an accelerating voltage of 100 V or less. This ZnO:Zn phosphor emits high-intensity green-white light when excited by a slow electron beam, and is used as a fluorescent film for fluorescent display tubes excited by slow electron beams.

A low-speed electron beam-excited fluorescent display tube (hereinafter abbreviated as a "fluorescent display tube") basically consists of an anode plate having a fluorescent film on one side, and a cathode opposite the fluorescent film. is sealed in a container with a vacuum inside, and the fluorescent film on the anode plate is excited by a slow electron beam (generally a slow electron beam with an accelerating voltage of 100V or less) emitted from the cathode. It causes light to emit light. Fluorescent display tubes having a fluorescent film made of the ZnO:Zn phosphor described above are widely used as display elements in desktop electronic calculators, various measuring instruments, and the like.

In recent years, as the field of use of fluorescent display tubes has expanded, it has become desirable to diversify the emission colors of fluorescent display tubes, and the development of fluorescent materials that emit light other than green under slow electron beam excitation has become active. It has been progressing. the result,
Several phosphors have been found that emit high-brightness colors other than green under excitation with slow electron beams, and one of these phosphors has the composition formula (Zn _1-x , Cd _x ). There is a silver-activated zinc sulfide cadmium phosphor represented by S:Ag (where x is a number satisfying the condition 0.65≦x≦1. The same applies hereinafter).

As disclosed in Japanese Patent Application Laid-Open No. 53-132489,
The above (Zn _1-x , Cd _x )S:Ag phosphor emits red light under slow electron beam excitation, and _the Ag activation amount is
Cd _x ) 8×10 ^-5 to 3×10 ^-4 for 1 g of S matrix
g, it emits particularly high brightness. and Ag
(Zn _1-x , Cd _x ) S whose activation amount is within the above range:
A red-emitting fluorescent display tube having a fluorescent film made of Ag phosphor has been put to practical use as a display element.

By the way, in order to form a fluorescent film on an anode plate during the production of fluorescent display tubes, conventionally the anode plate was placed in a suspension of phosphor dispersed in water.
A so-called sedimentation coating method is used, in which the phosphor is allowed to settle on the anode plate by its own weight, and then the water is removed and the coating is dried. In the production of the conventional red-emitting fluorescent display tube mentioned above, this precipitation coating method is also used to form a phosphor film made of (Zn _1-x , Cd _x )S:Ag phosphor on the anode plate. It is being By sedimentation coating method (Zn _1-x , Cd _x )
The formation of a fluorescent film made of S:Ag phosphor is described in detail in the above-mentioned Japanese Patent Laid-Open No. 132489/1989.

Recently, screen printing has come to be used in place of the precipitation coating method to form a fluorescent film on an anode plate in the production of fluorescent display tubes due to ease of production. This screen printing method involves preparing a phosphor ink by mixing a phosphor with a suitable organic binder, printing the phosphor ink on an anode plate by mimeographing, and then printing the resulting coating. This method involves baking at a temperature of 400 to 500°C to remove the organic binder and form a fluorescent film. However, the Ag activation amount (Zn _1-x ,
Cd _x ) 8×10 ^-5 to 3×10 ^-4 for 1 g of S matrix
It has been found that when a (Zn _1-x , Cd _x )S:Ag phosphor is formed into a phosphor film by screen printing, its luminous volatility is significantly reduced by baking. Therefore, (Zn _1-x , _Cd :Ag phosphor is strongly desired.

The present invention has been made in view of the above-mentioned circumstances, and exhibits high-intensity light emission under low-speed electron beam excitation. The object of the present invention is to provide a (Zn _1-x , Cd _x )S:Ag phosphor whose emission brightness does not decrease due to oxidation.

In order to achieve the above object, the present inventor (Zn _1-x ,
We conducted various studies on Cd _x ) S:Ag phosphors. As a result, the amount of Ag activation that has been used in the fluorescent film of conventional red-emitting fluorescent display tubes has been reduced to (Zn _1-x ,
Cd _x ) 8×10 ^-5 to 3×10 ^-4 for 1 g of S matrix
(Zn _1-x , Cd _x )S: Ag than Ag phosphor
Surprisingly, we found that the luminance of S:Ag phosphors with high activation concentrations (Zn _1-x , Cd _x ) increases rather than decreases when baked in the screen printing process. When adding and mixing an appropriate amount of indium oxide (In ₂ O ₃ ) to a (Zn _1-x , Cd _x ) S:Ag phosphor with a high active concentration, baking increases the luminance of the phosphor. They have found that there can be further improvements, and have completed the present invention based on these discoveries.

In the luminescent composition of the present invention, 3×10 ⁻⁴ to 5×10 ⁻³ g of Ag was activated with respect to 1 g of the (Zn _1-x , Cd _x )S matrix (Zn _1-x , Cd _x ). S:Ag phosphor and In ₂ O ₃ are mixed at a weight ratio of 7:3 to 99:1.

The (Zn _1-x , Cd _x )S:Ag phosphor, which is one of the components of the luminescent composition of the present invention, is generally produced by the method described below. That is, when zinc sulfide (ZnS) raw powder and cadmium sulfide (CdS) raw powder are mixed, ZnS raw powder is (1-
x) Proportion of moles (0.65≦x≦1)
A predetermined amount of silver compounds such as silver chloride (AgCl) and silver nitrate (AgNO ₃ ) are mixed into the raw mixed sulfide powder, and in some cases, an appropriate amount of a fluxing agent such as sodium chloride (NaCl) is added. 800 to 800 in a sulfidic atmosphere such as a hydrogen sulfide atmosphere or a sulfur-free atmosphere.
It is obtained by firing at a temperature of 1200°C for 1 to 5 hours. The amount of activator Ag in this (Zn _1-x , Cd _x )S:Ag phosphor is 3 x 10 ^-4 to 5 x 10 ^-3 g per 1 g of matrix (Zn _1-x , Cd _x )S. be. Note that the S:Ag phosphor with an x value smaller than 0.65 (Zn _1-x , Cd _x ) has extremely low emission brightness under slow electron beam excitation;
Furthermore, since the luminescent color is not red, it is not preferable as a component of the luminescent composition of the present invention. Note that silver halide (e.g.
When using a phosphor (AgCl) or a halide (eg, NaCl) as a fluxing agent, some of the halogen remains in the phosphor.

In ₂ O ₃ , which is the other component of the luminescent composition of the present invention, may be In ₂ O ₃ , a general reagent, or In ₂ O ₃ , a general reagent, or a sulfate, nitrate, chloride, etc. that can be easily oxidized at high temperatures. Calcination obtained by firing an indium compound that can be converted to In ₂ O ₃ at a temperature of 1500℃ or less in air, a neutral atmosphere, or a weakly reducing atmosphere.
In ₂ O ₃ is used. In ₂ O ₃ has an average particle size of 2 to 2
It is preferable to use particles with a particle diameter of 10 μm, and it is more preferable to use particles with a uniform particle size using a sieve or the like.

The luminescent composition of the present invention has the above-mentioned (Zn _1-x , Cd _x )
S: Ag phosphor and In ₂ O ₃ are mixed in a ball mill and mixer.
It can be obtained by thorough mixing using a mill or the like. Both are (Zn _1-x , Cd _x )S:Ag/
The weight ratio of In ₂ O ₃ is in the range of 7/3 to 99/1. (Zn _1-x , Cd _x ) S: Ag/In ₂ O ₃ value is
If it is smaller than 7/3, the absorption of the light emitted by the (Zn _1-x , Cd _x )S:Ag phosphor by In ₂ O ₃ , which is a non-luminescent component in the luminescent composition, increases and the luminance decreases. However, on the other hand, the value of (Zn _1-x , Cd _x )S:Ag/In ₂ O ₃ is 9
If it is larger than 9/1, the luminescent composition is (Zn _1-x ,
Cd _x )S: It becomes close to an Ag phosphor, and no improvement in luminance due to the addition of In ₂ O ₃ is observed. From the point of view of luminance (Zn _1-x , Cd _x )S:
The value of Ag/In ₂ O ₃ is particularly preferably in the range 17/3 to 19/1.

The drawing shows (Zn _{0.2 , Cd 0.8} ) in a fluorescent display tube with _a phosphor film using S _: Ag phosphor.
Cd ₀ . ₈ ) S: This is a graph showing the relationship between the Ag activation amount of the Ag phosphor and the luminescence brightness of the phosphor film. Curves a, b and _c indicate that _the phosphor film is Cd _0.8 )S _:
When the phosphor film is composed of only Ag phosphor and is formed by a precipitation coating method, the phosphor film consists of (Zn ₀ . ₂ ,
Cd ₀ . ₈ ) S: When the phosphor film is made of only Ag phosphor and is formed by screen printing method (baking temperature is 500°C), and when the phosphor film is made of (Zn ₀ . ₂ ,
Cd _0.8 ) S:Ag phosphor and In ₂ O ₃ are mixed in a weight ratio _of 9:1, and the phosphor film is formed by a screen printing method (baking temperature is 500℃). In the drawings, the emission brightness (vertical axis) is expressed as a relative value, and each fluorescent film was excited by a slow electron beam with an accelerating voltage of 50V.

As is clear from curve a, (Zn ₀ . ₂ , Cd ₀ . ₈ )
S: When the Ag phosphor is made into a phosphor film by the precipitation coating method, that is, when baking is not performed, the Ag activation amount is (Zn _{0. 2} , Cd _{0. 8} ) per 1 g of S matrix. When the concentration is 8×10 ^-5 to 3×10 ^-4 g, high luminance is exhibited, and in particular, the Ag activation amount is approximately 1.5× ₁₀ ^- per 1 g _of S matrix (Zn _0.2 , Cd _0.8 ). Maximum luminance is achieved at ⁴ g. As explained earlier, the Ag _activation amount is 8×10 ^-5 to 3× ₁₀ ^-4 g per 1 g of ₍ Zn _0.2 , Cd _0.8 )S matrix _{. 0.8} ) S:Ag phosphor has conventionally been put to practical use as a phosphor film _for red-emitting fluorescent display tubes. However, as is clear from curve b, when the conventional practical (Zn _0.2 , Cd _0.8 ) S:Ag phosphor is made into a phosphor film by screen printing, _that is, it is not subjected to baking _. In this case, the luminance of the emitted light decreases. However _, as is clear from _curve b, _the Ag activation concentration is higher than that of the conventional practical (Zn _0.2 , Cd _0.8 ) S: _{Ag phosphor .} :
Surprisingly, when Ag phosphors (which have not been put to practical use due to their low luminance) are made into a phosphor film by screen printing, that is, when they are baked, their luminance does not decrease; In fact, it improves significantly. And the Ag _activation amount is (Zn _0.2 ,
Cd _0.8 ) 8×10 ^-4 _to 5× per 1 g of S matrix
When the (Zn _0.2 , Cd _0.8 ) S:Ag phosphor with 10 ^-3 _g is made into _a phosphor film by screen printing, _the conventional practical (Zn _0.2 , Cd _{0.8) .8} ) S: Shows luminance equal to or higher than the maximum luminance of Ag phosphor.

In this way _, conventionally practical (Zn _0.2 , Cd _{0.8 )} S:Ag
Ag _activation concentration is higher than that of phosphor (Zn _0.2 , _{Cd 0.8} )
The luminance of the S:Ag phosphor is improved by baking in the screen printing process, and this improvement in luminance is facilitated by mixing an appropriate amount of In ₂ O ₃ into the phosphor. This situation is shown by curve c.

As is clear from the comparison between curve a and _curve b, the Ag activation amount is 2× ₁₀ ^-4 to 3×10 ^-4 g per 1 g of (Zn _0.2 , Cd _0.8 )S matrix. (Zn _{0.2 ,}
Cd ₀ . ₈ ) When the S:Ag phosphor is formed into a phosphor film by screen printing, the luminance of the light emission decreases. However, as is clear from curve c, the S:Ag phosphor whose Ag _activation amount is in the above range (Zn _0.2 , Cd _0.8 ) can be mixed with In _{2 O 3 to} The improvement in luminance is greater than the decrease in luminance due to the formation of a fluorescent film by screen printing, and therefore the Ag _activation amount is within the above range (Zn _0.2 , Cd ₀ . ₈ ) When a luminescent composition containing S:Ag phosphor mixed with In ₂ O ₃ is formed into a phosphor film by screen printing, the activation amount of Ag without baking is the same (Zn _{0 .2} , _{Cd 0.8} ) S: Shows higher luminance than the Ag phosphor (curve a). As is clear from curves c and a, the Ag activation amount (Zn ₀ . ₂ , Cd ₀ . ₈ ) is 3×10 ^-4 to 5× with respect to S1g.
10 ^-3 _g (Zn _0.2 , _{Cd 0.8} ) S:Ag phosphor and
When the luminescent composition mixed with In ₂ O ₃ is made into a fluorescent film by screen printing, the maximum _{luminescence of} the conventional practical (Zn _0.2 , Cd _0.8 )S:Ag phosphor mentioned above Indicates luminescence brightness that is higher than luminance. The Ag activation amount of the (Zn _1-x , Cd _x )S:Ag phosphor used in the luminescent composition of the present invention is 3×10 ^-4 with respect to 1 g of the (Zn _1-x , Cd _x )S matrix. It is based on this knowledge that the amount is limited to 5×10 ^-3 g.

In addition, by mixing an appropriate amount of In ₂ O ₃ into the (Zn _1-x , Cd _x )S:Ag phosphor, (Zn _1-x , Cd _x )
The emission brightness of the S:Ag phosphor under slow electron beam excitation is improved by mixing In ₂ O ₃ , which has higher conductivity than the (Zn _1-x , Cd _x )S:Ag phosphor. The conductivity of the (Zn _{1 -x} , Cd _x )S:Ag phosphor _is improved by This is thought to be because the phosphor no longer exhibits a charge-up phenomenon and the excitation efficiency of the (Zn _1-x , Cd _x )S:Ag phosphor is improved.

_Regarding the above (Zn _{0.2 ,} Cd _0.8 ) S _: Ag phosphor and the (Zn _0.2 , _{Cd 0.8} ) S:Ag/In ₂ O ₃ value of 9/1, the luminescent composition As described in detail, (Zn _1-x , Cd _x ) S:Ag phosphor with x other than 0.8 and (Zn _1-x , Cd _x ) S:Ag phosphor with x other than 0.8 and In ₂ O Regarding the luminescent composition consisting of a _mixture with (Zn _1-x ,
The relationship _{between the Ag activation} amount of _Cd (Zn _{0.2 ,} Cd _{0.8 )} S:Ag _{/ In 2} O ₃ of 9/1 _{. .8} ) S: Ag/In ₂ O ₃ value is 7/3 to 99/
It was confirmed that even if (Zn _1-x , Cd _x ) was changed within the range of 1, the relationship between the Ag activation amount and luminance of the S:Ag phosphor did not change much.

As explained above, the present invention provides a luminescent composition which, when formed into a fluorescent film for a fluorescent display tube by screen printing, provides a fluorescent film that emits high-intensity light. The luminescent composition of the present invention has great industrial utility value as a substitute for the (Zn _1-x , Cd _x )S:Ag phosphor that has been used as a fluorescent film for conventional red-emitting fluorescent display tubes. It is.

Next, the present invention will be explained with reference to Examples.

Example 1 (Zn _0.2 , Cd _0.8 )S _: Ag phosphor 9 with Ag activation amount of 10 ⁻³ g _per 1 g _of ( _{Zn 0.2} , Cd _0.8 )S matrix
parts by weight and 1 part by weight of In ₂ O ₃ powder with an average particle size of 3 μm (reagent manufactured by Hikotaro Moritake Shoten) were sufficiently mixed in a ball mill to _obtain (Zn _0.2 , Cd _0.8 ) S:Ag/In _. A luminescent composition having a mixing weight ratio of ₂ O ₃ of 9/1 was obtained.

A luminescent composition ink was prepared by thoroughly kneading 20 g of the luminescent composition thus obtained with a binder consisting of 10 g of diacetone alcohol and 0.1 g of nitrocellulose in a ball mill. Next, the luminescent composition ink was printed on one side of a 2 cm square aluminum anode plate using a 300 mesh Tetron mesh screen so that the coating density after baking was about 3 mg/cm ² , and then the coating film was applied. 500℃
The binder was decomposed and removed by baking for 30 minutes in an electric furnace kept at a temperature of
) was formed.

Separately, for comparison, the Ag activation amount was 1.5×10 ^-4 g per 1 g of (Zn _0.2 , _{Cd 0.8} ) S matrix _.
(Zn _0.2 , _{Cd 0.8} ) S:Ag phosphor _100mg
Using a suspension dispersed in 100 c.c. of distilled water containing 0.01% water glass, a coating density of approximately 3 mg after drying was applied to one side of a 2 cm square aluminum anode plate by the sedimentation coating method. After coating the above (Zn ₀ . ² , _{Cd 0 .} R) was formed.

Fluorescent film A and fluorescent film R obtained as described above
When excited with a slow electron beam of 50V, fluorescent film A exhibited luminance approximately 1.7 times that of fluorescent film R.

Example 2 (Zn _0.2 , Cd _0.8 )S _: Ag phosphor with Ag activation amount of 5×10 ⁻³ _g per 1 g of ( _{Zn 0.2 ,} Cd _0.8 )S matrix (Zn ₀ . ₂ , Cd ₀ . ₈ ) obtained in the same _manner as in Example ₁ using
Example 1 except that the luminescent composition of Example 1 was used.
In the same manner as above, a fluorescent film (hereinafter referred to as fluorescent film B) was formed on one entire surface of a 2 cm square aluminum anode plate by screen printing.

When the fluorescent film B obtained as described above and the fluorescent film R formed by the precipitation coating method in Example 1 were excited with a 50V slow electron beam, the fluorescent film B was different from that of the fluorescent film R. about
It showed 1.3 times the luminescence brightness.

Example 3 (Zn _0.2 , Cd _0.8 )S _: Ag phosphor with Ag activation amount of 3×10 ^-4 g per 1 g _of ( _{Zn 0.2} , Cd _{0.8 )} S matrix (Zn ₀ . ₂ , Cd ₀ . ₈ ) obtained in the same _manner as in Example ₁ using
Example 1 except that the luminescent composition of Example 1 was used.
In the same manner as above, a fluorescent film (hereinafter referred to as fluorescent film C) was formed on one entire surface of a 2 cm square aluminum anode plate by screen printing.

When the fluorescent film C obtained as described above and the fluorescent film R formed by the sedimentation coating method in Example 1 were excited with a 50V slow electron beam, the fluorescent film C was different from that of the fluorescent film R. about
The luminescence brightness was 1.2 times higher.

Example 4 (Zn _0.25 , _{Cd 0.75} )S: _Ag with Ag activation amount of 8×10 ^-4 g per 1 g _{of (Zn 0.25 , Cd 0.75 ) S matrix}
Calcined In ₂ with an average particle size of 5μ was obtained by baking 17 parts by weight of the phosphor and In ₂ O ₃ reagent (manufactured by Morizuki Hikotaro Shoten) in air at a temperature of 1400°C for 1 hour, and then sieving to make the particle size uniform. (Zn _0.25 , Cd 0.75 ) obtained in the same manner as in Example 1 using 3 parts by weight of O ₃ and a luminescent composition in which the mixing weight ratio of (Zn _0.25 , _{Cd 0.75} ):Ag/In ₂ O ₃ was 17/3. A fluorescent film (hereinafter referred to as fluorescent film D) was formed on one entire surface of a 2 cm square aluminum anode plate by screen printing in the same manner as in Example 1 except that a fluorescent film was used.

Separately, for comparison, the Ag activation amount was 1.5× _{10 -4} g for 1 g of (Zn _0.25 , Cd _0.75 ) S matrix ^.
(Zn _0.25 , _{Cd 0.75} )S:Ag phosphor was used in the same manner as in _Example 1, except that the phosphor was deposited on one side of a 2 cm square aluminum anode plate. Fluorescent film (hereinafter referred to as fluorescent film S)
) was formed.

Fluorescent film D and fluorescent film S obtained as described above
When excited with a slow electron beam of 50V, the fluorescent film D exhibited luminance about 1.6 times that of the fluorescent film S.

[Brief explanation of the drawing]

_The drawing shows (Zn _1-x , Cd _x ) in a fluorescent display tube with a fluorescent film using S:Ag phosphor.
_Cd
b and c are fluorescent films (Zn _1-x , Cd _x ), respectively.
S: When the phosphor film is made of only Ag phosphor and is formed by the precipitation coating method, the phosphor film consists of (Zn _1-x ,
Cd _x )S:Ag _{phosphor and} the phosphor film formed by screen printing, This is a case where the fluorescent film is made of a luminescent composition mixed with ₂ O ₃ and is formed by a screen printing method.

Claims (1)

[Claims] 1. Zinc cadmium sulfide having the compositional formula (Zn _1-x , Cdx)S (where x is a number satisfying the condition 0.65≦x≦1.0) is used as a matrix, and 1 g of this matrix is Silver-activated zinc sulfide cadmium phosphor [(Zn _1-x , Cdx)S:Ag] containing 3×10 ^-4 to 5×10 ^-3 g of silver as an activator and indium oxide (In ₂ O ₃ ) in a weight ratio of 7:3 to 99:1. 2 The mixing weight ratio of the silver-activated zinc sulfide cadmium phosphor and the indium oxide is 17:3 to 19:
1. The luminescent composition according to claim 1, characterized in that: