JP2002080844A - Electroluminiscent material and electroluminiscent device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electroluminiscent material which effects a blue light emission having excellent color purity, and an electroluminiscent device using the material in the light-emitting layer. SOLUTION: The electroluminiscent material is represented by the composition formula: CaXSr1-XS: Bi3+ (X is a real number in the range of 0<=X<=1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent (EL) material which emits light by application of an electric field and an electroluminescent device (EL device) using the same, and more particularly, to a thin film EL material used for a light emitting layer of the EL device. The present invention also relates to a thin film EL device using this material and an EL device in which a thin film of the above material is formed on a ceramic substrate.

[0002]

2. Description of the Related Art Hitherto, in order to realize a full-color thin film EL display device, EL materials which emit red, green, and blue light have been developed. However, among these EL materials, those which can be easily manufactured industrially for blue and have sufficient color purity have not been obtained so far.

For example, a thin film EL device using MGa ₂ S ₄ : Ce (M; alkaline earth metal) as an EL material has been developed and has attracted attention due to its good color purity (Japanese Patent Laid-Open No. 5-654).
No. 78). For example, the chromaticity coordinates in the case of SrGa ₂ S ₄ : Ce are (x = 0.15, y = 0.10) (Reference 1: WABarrow, et.al., SID'93 Digest, p. 7
61, 1993). Recently, BaAl ₂ S ₄ : Eu has been used as a blue EL material having good color purity by N.I. It has been reported by Miura et al. (Reference 2: N. Miura et.al. Jp
nJAppl.Phys.38 [11B] (1999) L1291). BaAl ₂ S ₄ :
The chromaticity coordinates of the thin film EL element of Eu are (x = 0.12, y =
0.10).

However, these Mga ₂ S ₄ and BaAl ₂
Constituent elements of the base material S ₄ is, II group respectively, IIIb group, V
They belong to different groups of the Ib group and are composed of three elements with different chemical properties. So 1: 2: 4
It is difficult to prepare a compound thin film having a precise composition ratio. Therefore, there is a demand for an EL material that is industrially easy to manufacture, has a simpler chemical composition, and emits blue light.

Heretofore, as a base material, II-VI having a chemical composition consisting of two simple elements of only Group II and Group VIb has been used.
Blue EL materials of group b compounds have been actively developed. SrS: Ce was once proposed as a promising blue EL material (see US Pat. No. 4,751,427). However, a problem with SrS: Ce is that its EL emission has emission of blue-green chromaticity (x = 0.26, y = 0.36), and the color purity of blue is poor.

[0006] Recently, SrS: Cu has also been proposed as a blue EL material (Reference 3: S.-S.Sun, et.al., SI
D'97 Digest, p.301, 1997). However, this SrS: C
As for the problem with u, the EL emission is blue-green chromaticity coordinates (x = 0.16 to 0.20, y = 0.26 to 0.32).
And that the blue color purity is poor. In order to improve this color purity, Ag co-added S
rS: Cu, Ag was recently proposed (Ref. 4: S.-
S. Sun, Displays 19 (1999) 145). Sr with co-added Ag
S: The chromaticity coordinates of Cu and Ag are (x = 0.17, y =
0.13) and the blue color purity is improved (Reference Document 4). However, by adding Ag, the impurity compound AgxSy (x and y are real numbers) is easily formed in the thin film, and the unevenness of the thin film surface is increased, so that the EL element is likely to be broken. 5: K.-O.Velth
aus, et.al., Euro Displays '99 Proc., p.247, 1999). Also recently, CaS: Pb has been proposed as another blue material (Ref. 5: SJYun, et.al., SID '99 Dige).
st, p.1142, 1999). The chromaticity coordinates of the CaS: Pb EL emission are (x = 0.14 to 0.15, y = 0.07 to 0.1).
5) and blue EL emission with good color purity. But,
This CaS: Pb uses a highly toxic material called Pb, and is not a preferable material for use in general display devices.

As described above, with respect to the blue EL material, a blue-emitting EL material which is easily manufactured industrially, exhibits a pure blue color purity, and is safe as a general display device is presently available. It has not been obtained by now.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide an EL material which emits blue light with excellent color purity and an EL device using the material in a light emitting layer.

Another object of the present invention is to provide a material having a pure blue color purity which is easily manufactured industrially and is safe as a general display device.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0011]

The outline of the invention disclosed in the present application is briefly described as follows.

(1) An EL material represented by the composition formula Ca _X Sr _{1 -X} S: Bi ³⁺ (where X is a real number in the range of 0 ≦ X ≦ 1).

(2) The composition formula is CaS: Bi ₂ S ₃ , S
rS: Bi ₂ S ₃ , CaS: BiF ₃ , SrS: BiF ₃ ,
An EL material selected from CaS: BiCl ₃ and SrS: BiCl ₃ .

(3) An EL material doped with one or more ions of Li ⁺ , Cu ⁺ , and Na ⁺ as a Bi ³⁺ charge compensator in the above composition formula.

(4) A thin-film EL device using any one of the above-mentioned means (1) to (3) for the light-emitting layer.

(5) An EL device in which a thin film of any one of the above-mentioned means (1) to (3) is formed on a ceramic substrate and used as a light emitting layer.

The EL device of the present invention is, for example, CaS: B
The chromaticity coordinates of the luminescence of the EL element using the i ³⁺ thin film for the light-emitting layer were (x = 0.15, y = 0.15), indicating good blue luminescence. This chromaticity coordinate is expressed as MGa ₂ S ₄ : Ce or Ba
Al ₂ S ₄ : comparable to the chromaticity coordinates of a blue EL material such as Eu. Moreover, when the composition of the base material is MGa ₂ S ₄ or BaAl ₂ S ₄
Compared with materials that require precise control of the composition ratio of 1: 2: 4, such as II-VIb group compounds having a chemical composition consisting of two simple elements of only group II and group VIb, they are easy to manufacture. Becomes

Furthermore, blue color purity is better than that of SrS: Ce or SrS: Cu which emits blue-green light using a conventional II-VIb group compound. The CaS: Bi ³⁺ thin film is S
Ag, which causes film quality degradation in the case of rS: Cu, Ag, is not used, and toxic Pb, which is a problem with CaS: Pb, is not used.

Hereinafter, the present invention will be described in detail with reference to the drawings together with embodiments (examples) according to the present invention.

[0020]

(Embodiment 1) As a first embodiment of a light emitting layer material of an electroluminescence (EL) element according to the present invention, when CaS: Bi ³⁺ is used, a thin film of the material is vacuum-deposited. The following is an explanation of an example produced by the method described above.

In order to produce a CaS: Bi ³⁺ thin film,
Although various combinations of evaporation materials are possible, in the first embodiment,
An example of the case of manufacturing with a combination of Ca, ZnS, and Bi ₂ S ₃ raw materials will be described.

In a vacuum deposition film forming apparatus,
K (Knudsen) cell for supplying vapor of metal material Ca
, K cell for supplying compound ZnS vapor, and compound
Bi _TwoS_ThreeAnd a K cell for supplying steam.

The substrate temperature is 470 ° C., the heating temperature of the Ca K cell is 500 ° C., and the heating temperature of the ZnS K cell is 860 ° C.
Then, a reaction represented by the following chemical reaction formula occurs on the substrate.

Ca + ZnS → CaS + Zn Zn generated by this reaction has a relatively high vapor pressure, and thus re-evaporates on the substrate, so that only a CaS thin film can be formed on the substrate.

Further, Bi ₂ S _{3 is used} as an impurity dopant.
When the heating temperature of the K cell is heated to 300 ° C., Bi ₂ S ₃ is taken into the CaS thin film, and a CaS: Bi ³⁺ (or CaS: Bi ₂ S ₃ ) thin film grows.

Using this CaS: Bi ³⁺ thin film for the light emitting layer, a thin film EL device as shown in FIG. 1 was produced.

As shown in FIG. 1, a lower electrode (transparent electrode) 2 is formed on a glass substrate 1 as shown in FIG.
Are formed on the lower electrode 2, and the lower insulating layers 31, 3
2 (3) are formed. A buffer layer 51 (5) is formed on the lower insulating layer 32, and the light emitting layer 4 made of the CaS: Bi ³⁺ thin film is formed on the buffer layer 51. A buffer layer 52 (5) is formed on the light emitting layer 4, and an upper insulating layer 61 (6) covers the light emitting layer 4 and the buffer layers 51 and 52 (5) on the buffer layer 52. Is formed. An upper insulating layer 62 (6) is formed on the upper insulating layer 61,
An upper electrode (back electrode) 7 is formed on the upper insulating layer 62. The thin-film EL device thus manufactured exhibited blue electroluminescence.

FIG. 2 shows the emission spectrum of this thin film EL device.
Shown in It can be seen from FIG. 2 that the emission peak is mainly in the blue region. The chromaticity coordinates at this time are (x = 0.15, y
= 0.15), and the luminance is about 1 cd when driven at 1 kHz.
/ M ² .

(Embodiment 2) As Embodiment 2 of the light emitting layer material of the EL device according to the present invention, an example in which a thin film of the material is produced by vacuum deposition in the case of using SrS: Bi ³⁺ will be described. In order to produce an SrS: Bi ³⁺ thin film, various combinations of evaporation materials are possible. In this embodiment, an example in which a combination of Sr, Ga ₂ S ₃ , and BiF ₃ is used will be described.

In the second embodiment, as in the first embodiment, in the vacuum deposition apparatus, a K cell for supplying the vapor of the metal raw material Sr and a vapor of the compound Ga ₂ S ₃ are supplied into the apparatus. A K cell and a K cell that supplies vapor of the dopant material BiF ₃ are arranged.

The substrate temperature is 470 ° C., the heating temperature of the Sr K cell is 480 ° C., and the heating temperature of the Ga ₂ S ₃ K cell is 940.
When the temperature is set to ° C., a reaction represented by the following chemical reaction formula occurs on the substrate.

Sr + Ga ₂ S ₃ → SrS + 2GaS Since GaS generated by this reaction has a relatively high vapor pressure, it re-evaporates on the substrate, and only the SrS thin film can be formed on the substrate.

Further, BiF _{3 is used} as an impurity dopant.
When the heating temperature of the K cell is heated to 360 ° C., BiF ₃ is taken into the SrS thin film, and a SrS: Bi ³⁺ (or SrS: BiF ₃ ) thin film grows.

Using this SrS: Bi ³⁺ thin film for the light emitting layer, a thin film EL device as shown in FIG. 1 was produced.

This thin film EL device exhibited blue electroluminescence. The emission spectrum is shown in FIG.
The chromaticity coordinates at this time were (x = 0.18, y = 0.33), and the luminance was about 1 cd / m ² when driven at 1 kHz.

(Example 3) CaS: Bi in Example 1
³⁺In Example 2, SrS: Bi³⁺The light emitting layer material of the EL element
The example of the case of using
As an example, Ca _XSr_1-XS: Bi³⁺(However, X is 0 ≦
Real number in the range of X ≦ 1). This material is vacuum deposited
When manufacturing, several combinations are considered as evaporation materials.
Table 1 shows examples of these combinations. Table 1
Contains trivalent Bi³⁺As a charge compensating agent for
Li metal ion Cu⁺, Li⁺, Na⁺Of charge compensating agent
Examples of raw materials are also provided.

[0037]

[Table 1] As an example of the light emitting layer of Table 1, Ca _0.5 Sr _0.5 S: Bi ³⁺ ,
An example in which a Cu ⁺ thin film is manufactured by a vacuum evaporation method will be described.

In the vacuum deposition apparatus, a K cell for supplying a vapor of a metal material Ca, a K cell for supplying another metal material Sr, a K cell for supplying a vapor of a compound ZnS, a dopant, A K cell for supplying the vapor of the raw material Bi ₂ S ₃ and a K cell for supplying the vapor of the charge compensating material Cu ₂ S are arranged.

The substrate temperature was 470 ° C., the heating temperature of the Ca K cell was 500 ° C., the heating temperature of the Sr K cell was 480 ° C.
When the heating temperature of the nS K cell is set to 860 ° C., on the substrate, Sr + Ca + 2ZnS → 2Sr _0.5 Ca _0.5 S + 2Zn Since the Zn generated by this reaction has a relatively high vapor pressure, it re-evaporates on the substrate, and Sr _0.5 Ca Only a _0.5S thin film can be formed on a substrate.

Further, Bi ₂ S _{3 is used} as an impurity dopant.
When the heating temperature of the K cell was heated to 300 ° C. and the heating temperature of the K cell of Cu ₂ S was heated to 875 ° C. as a charge compensating agent, Bi ³⁺ and Cu ⁺ were taken into the Sr _0.5 Ca _0.5 S thin film. , Ca _0.5 Sr _0.5 S: Bi ³⁺ , Cu ⁺ (or S
r _0.5 Ca _0.5 S: Bi ₂ S ₃ , Cu ₂ S) thin film grows.

Using this Ca _0.5 Sr _0.5 S: Bi ³⁺ , Cu ⁺ thin film as a light emitting layer, a thin film EL device as shown in FIG. 1 was produced.

This EL device exhibited blue electroluminescence. FIG. 4 shows the emission spectrum. The chromaticity coordinates at this time were (x = 0.15, y = 0.10), and the luminance was about 10 cd / m ² when driven at 1 kHz.

In the above embodiment, an example in which a vacuum evaporation method is used for producing a light emitting layer thin film has been described. However, other production methods include an electron beam evaporation method, a sputtering method, a CVD method, a MOCVD method, and an MB method.
E method, MOMBE method, or the like may be used.

Further, the present invention can be applied to a case where a ceramic substrate is used as a substrate of an EL element.

As described above, the invention made by the present inventor is:
Although the present invention has been described in detail with reference to the embodiment, the present invention is not limited to the embodiment, and it is needless to say that various changes can be made without departing from the scope of the invention.

[0046]

The effects obtained by the invention disclosed in the present application will be briefly described as follows.

According to the present invention, it is possible to obtain an EL material which emits blue light with excellent color purity and an EL element using the material for a light emitting layer.

Further, it is possible to obtain a material having a pure blue color purity which is easily manufactured industrially and is safe as a general display device.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a schematic structure of a thin-film EL device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an emission spectrum of a thin-film EL device using a CaS: Bi ³⁺ thin film of the first embodiment as a light-emitting layer.

FIG. 3 is a diagram showing an emission spectrum of a thin-film EL device of the second embodiment having a SrS: Bi ³⁺ thin film as a light-emitting layer.

FIG. 4 shows Ca _0.5 Sr _0.5 S: Bi ³⁺ , Cu of Example 3
It is a figure which shows the emission spectrum of the thin film EL element which made the ⁺ thin film the light emitting layer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass substrate 2 ... Lower electrode (transparent electrode) 3 (31, 32) ... Lower insulating layer 4 ... Light emitting layer 5 ... Buffer layer 6 (61, 6)
2) Upper insulating layer 7 Upper electrode (back electrode)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoji Inoue 1-10-11 Kinuta, Setagaya-ku, Tokyo Japan Broadcasting Corporation Research Institute (72) Inventor Isao Tanaka 1-10-11 Kinuta, Setagaya-ku, Tokyo No. Japan Broadcasting Corporation Broadcasting Research Institute (72) Inventor Yoshitaka Izumi 1-10-11 Kinuta, Setagaya-ku, Tokyo F-term in Japan Broadcasting Corporation Broadcasting Research Institute 3K007 AB04 CA01 CB01 DA05 DB01 DC00 EA02 4H001 XA16 XA20 XA38 YA83

Claims (5)

[Claims] A composition formula Ca _X Sr _{1 -X} S: Bi ³⁺ (where,
X is a real number in the range of 0 ≦ X ≦ 1). 2. The composition according to claim 1, wherein the composition formula is CaS: Bi ₂ S ₃ , Sr.
S: Bi ₂ S ₃ , CaS: BiF ₃ , SrS: BiF ₃ , C
aS: BiCl _3, SrS: electroluminescent material according to claim 1, characterized in that it is selected from BiCl _3. 3. The composition formula according to claim 1, wherein one or more ions of Li ⁺ , Cu ⁺ , and Na ⁺ are doped as a Bi ³⁺ charge compensating agent. Electroluminescent material. 4. A thin-film electroluminescence device using the electroluminescence material according to claim 1 for a light-emitting layer. 5. An electroluminescent device comprising a thin film of the electroluminescent material according to claim 1 formed on a ceramic substrate and used as a light emitting layer.