JP2586583B2 - Organic phosphor for organic thin film EL devices - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an organic phosphor for an organic thin-film EL device, and more particularly to an organic phosphor for an organic thin-film EL device used for a flat light source or a display. Things.

[Prior Art] An EL (electroluminescence) element using an organic substance as a raw material has attracted attention as an inexpensive large-area full-color display element. Although this organic EL device was actively studied for a period of time, it did not reach practical use because of its lower luminance and severely deteriorated characteristics as compared with a ZnS: Mn-based inorganic thin film EL device.
In addition, the drive voltage was as high as about 100 V DC, which was an obstacle to practical use.

However, recently, a new type of organic thin film EL device in which an organic thin film has a two-layer structure has been reported and has attracted strong interest (Applied Physics Letters, Vol. 51, p. 913, 1987). According to reports, this organic thin film EL device
As shown in FIG. 1, a fluorescent metal chelate complex is used for an organic phosphor thin film layer 4 and an amine-based material is used for a charge injection layer 3 to form a two-layer structure, which is sandwiched between a transparent electrode 2 and a back electrode 5. Discloses that a bright green light was emitted, and a luminance of several hundred cd / m ² was obtained by applying a DC voltage of 6 to 7 V. The maximum luminous efficiency is 1.5lm / W, which is close to the practical level.

[Problems to be Solved by the Invention] As described above, an organic thin film EL device having a multilayer structure of an organic phosphor thin film and a charge injection layer has obtained very bright green light emission, and is characterized by this device. The organic phosphor thin film material is tris (8-oxyquinolinato) aluminum. As described above, there is an organic phosphor for an organic thin film EL device capable of obtaining a practical luminance level in green light emission. In order to perform full-color display, red and blue light emission are required. However, it has been difficult for organic phosphors developed so far to emit various emission colors at a practical luminance level.
For example, anthracene or the like has been reported as a material having another emission color. However, the organic thin-film EL device using this as an organic phosphor has a very weak light emission (for example,
(Solid Films, vol. 94, p. 171, 1982, and Japanese Applied Physics, vol. 27, p. L269, 1988). Therefore, although a new organic phosphor is absolutely necessary for practical use of a full-color organic thin-film EL device, there is no suitable substance among the conventional organic phosphors.

The present invention has been made in view of the above-described conventional circumstances, and has as its object to provide an organic phosphor for an organic thin-film EL device capable of performing full-color display at a practical level.

[Means for Solving the Problems] The present invention provides an organic thin-film EL device comprising a metal complex having a ligand in which at least one or more condensed rings are formed on 8-hydroxyquinoline as a ligand. Organic phosphor.

Here, the central metal constituting the metal complex is aluminum, beryllium, magnesium, calcium, zinc, cadmium, chromium, nickel, bismuth, indium, thallium, titanium, tin, vanadium, rhodium, lead, iron, silver, copper , Strontium, barium, scandium, gallium, yttrium, and cobalt.

The reason why a metal complex having 8-hydroxyquinoline as a ligand exhibits particularly strong emission is that the lone pair of nitrogen of 8-hydroxyquinoline flows into the metal, and the lowest excited singlet state and lowest excited triplet state of the complex are changed. Very pure π−
This is because it is close to the π ′ excited state. Therefore, 8
-If the complex structure portion of hydroxyquinoline and metal is retained, the emission intensity in EL emission is retained. The present inventors have searched for a new organic phosphor for an organic thin-film EL device based on the above research results, and as a result, the organic phosphor characterized by the above-described structure has an emission wavelength without changing the emission intensity. It has been found that the emission wavelength of a metal complex having 8-hydroxyquinoline as a ligand can be changed to the longer wavelength side.

The substance as the organic light emitting substance for the organic thin film EL element of the present invention,
For example, examples of the organic compound include an aromatic amine and an aromatic polyamine compound as the hole transfer layer, and a compound having a quinone structure, tetracyanoquinodimethane, and tetracyanoethylene as the electron transfer layer. Examples of the charge injection layer of an inorganic compound include a P-type or N-type group IV, III-V, and II-VI compound semiconductor. The organic substance or the inorganic substance used as the charge injection layer can be selected from these compounds as needed.

[Example] Hereinafter, the present invention will be described using an example.

Example 1 A 3-fold equivalent amount of 1-aza-10-hydroxy-anthracene dissolved in ethanol was dropped into an aqueous solution of aluminum nitrate-9-hydrate. After stirring this solution for 3 hours,
Dilute sodium hydroxide was added dropwise until the pH reached 8. In this case, after filtering the precipitate that has precipitated, a metal complex having aluminum as a central metal is desirable in dilute aqueous sodium hydroxide. This is because the aluminum complex has a particularly high emission intensity. However, it is also possible to slightly change the basic emission wavelength by changing the central metal.

Next, some general formulas are given as examples of the organic phosphor according to the present invention.

(In the formula, M represents an n-valent metal ion and X represents an n / m-valent anion.) In the present invention, the substrate was thoroughly washed with a liquid used as a charge injection layer. The obtained compound was thoroughly dried at 70 ° C. under reduced pressure. The solution of the metal complex thus obtained is 51
It showed fluorescence centered at 0 nm.

Next, 1,1-bis (4-N, N-ditolylaminophenyl) cyclohexane of 800 ° was deposited as a charge injection layer on the transparent electrode formed on the glass substrate, and then obtained by the above procedure. 500 と し て metal complex as organic phosphor layer
Evaporated. A magnesium / aluminum alloy was deposited thereon as a negative electrode. Examination of the emission characteristics of the obtained organic thin film EL element, luminescence of 0.05 mW / cm ² was obtained at 3mA / cm ^2. The emission color was slightly yellow-green, and could be shifted to a longer wavelength side as compared with the case where an organic fluorescent material of tris (8-oxyquinolinato) aluminum was used.

Reference Example A 3-fold equivalent of 8-quinolinol dissolved in ethanol was dropped into an aqueous solution of aluminum nitrate-9-hydrate.
After stirring this solution for 3 hours, dilute sodium hydroxide was added.
It was added dropwise until the pH reached 8. In this case, the precipitate that had precipitated was filtered and washed well with a dilute aqueous sodium hydroxide solution. The obtained compound was thoroughly dried at 70 ° C. under reduced pressure. The solution of the metal complex thus obtained is 475n
The fluorescence has a center at m, and the physical properties are based on literature values (R. Balla
rdiri et al., Inorganic Chemistry, 25, 3858
Page, 1986).

After depositing 800Å of 1,1-bis (4-N, N-ditolylaminophenyl) cyclohexane as a charge injection layer on a transparent electrode formed on a glass substrate, the metal complex obtained by the above procedure was deposited. 500Å was deposited as an organic phosphor layer. A magnesium / aluminum alloy was deposited thereon as a negative electrode. Examination of the emission characteristics of the obtained organic thin film EL element, luminescence of 0.05 mW / cm ² was obtained at 3mA / cm ^2. The emission color was green.

Example 2 In an aqueous solution of aluminum nitrate-9-hydrate, a three-fold equivalent amount of 12-aza-11-hydroxynaphthacene dissolved in ethanol was added dropwise. After stirring the solution for 3 hours, dilute sodium hydroxide was added dropwise until the pH reached 8. In this case, the precipitate that had precipitated was filtered and washed well with a dilute aqueous sodium hydroxide solution. The obtained compound was thoroughly dried at 70 ° C. under reduced pressure.

Next, 800Å of 1,1-bis (4-N, N-ditolylaminophenyl) cyclohexane was deposited as a charge injection layer on the transparent electrode formed on the glass substrate, and then the metal obtained by the above procedure was deposited. The complex was vapor-deposited at 500 ° as an organic phosphor layer. A magnesium / aluminum alloy was deposited thereon as a negative electrode. Examination of the emission characteristics of the obtained organic thin film EL element, luminescence of 0.05 mW / cm ² was obtained at 3mA / cm ^2. The emission color was orange.

Example 3 In an aqueous solution of aluminum nitrate-9-hydrate, 3 times the equivalent of 13-aza-14-hydroxypentacene dissolved in ethanol was added dropwise. After stirring the solution for 3 hours, dilute sodium hydroxide was added dropwise until the pH reached 8. In this case, the precipitate that had precipitated was filtered and washed well with a dilute aqueous sodium hydroxide solution. The obtained compound was thoroughly dried at 70 ° C. under reduced pressure.

Next, 800 μm of N, N′-metamethylphenylbenzidine was deposited as a charge injection layer on the transparent electrode formed on the glass substrate, and then the metal complex obtained in the above procedure was deposited as a 500 μl organic phosphor layer. did. A magnesium / aluminum alloy was deposited thereon as a negative electrode. When the light emission characteristics of the obtained organic thin film EL device were examined, it was 0.04 mW
/ emission cm ² was obtained at 3mA / cm ^2. The emission color was red.

Example 4 A 3-fold equivalent amount of 1-aza-10-hydroxyanthracene dissolved in ethanol was dropped into an aqueous solution of bismuth nitrate pentahydrate. After stirring the solution for 3 hours, dilute sodium hydroxide was added dropwise until the pH reached 8. In this case, the precipitate that had precipitated was filtered and washed well with a dilute aqueous sodium hydroxide solution. The obtained compound was obtained under reduced pressure.
Dry well at 70 ° C.

On the transparent electrode formed on the glass substrate, 800 ジ ン of N, N'-metamethylphenylbenzidine was deposited as a charge injection layer, and then the metal complex obtained by the above procedure was deposited as an organic phosphor layer at 500Å. . A magnesium / silver alloy was deposited thereon as a negative electrode. Organic thin film obtained
When the luminescence characteristics of the EL element were examined, a luminescence of 0.04 mW / cm ² was found.
Obtained at 3 mA / cm ² . The emission color was slightly yellowish green.

[Effects of the Invention] As described above, by using the organic phosphor for an organic thin film EL device according to the present invention, the emission wavelength can be changed without changing the good luminous efficiency. It is extremely useful for full color devices. As described above, according to the present invention, the organic thin-film EL device can be raised to a practical level, and an inexpensive and large-area full-color display device can be provided, and its industrial value is high.

[Brief description of the drawings]

 FIG. 1 is a sectional view of a typical organic thin film EL device. DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 2 ... Transparent electrode 3 ... Charge injection layer, 4 ... Organic phosphor thin film layer 5 ... Back electrode

Claims (2)

(57) [Claims] 1. An organic phosphor for an organic thin-film EL device, comprising a metal complex having a ligand in which at least one condensed ring is formed on 8-hydroxyquinoline as a ligand. 2. The central metal constituting the metal complex is aluminum, beryllium, magnesium, calcium, zinc,
Cadmium, chromium, nickel, bismuth, indium, thallium, titanium, tin, vanadium, rhodium,
The organic phosphor according to claim 1, wherein the phosphor is at least one of lead, iron, silver, copper, strontium, barium, scandium, gallium, yttrium, and cobalt.