JP3936479B2 - Thin film electroluminescent material - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a thin film electroluminescence (EL) material that emits light when an electric field is applied, and particularly to a material used for a thin film light emitting layer.
[0002]
[Prior art]
For full colorization of a thin-film EL panel, research on an EL light emitting layer material exhibiting blue with high luminance and good color purity is underway. To date, it can be said that SrS: Ce is almost the only material that has reached the point of practical use. There are various SrS: Ce film forming methods such as sputtering, EB vapor deposition, and ALE, but industrially superior methods among them include Sr, S, Ce, etc. from different sources. In many cases, SrS: Ce itself is used as a source. In this case, it is considered that the physical properties of the film forming source have a great influence on the physical properties of the film, and in order to obtain a high quality film, it is indispensable to improve the quality of the source.
[0003]
Conventionally, SrS: Ce has been obtained by firing SrCO3 several times in H2 S at a temperature of 900-1180 DEG C. before and after addition and mixing of the Ce compound. SrS: Ce obtained by this method often exhibits an emission spectrum as shown by curve a in FIG. 1 when excited at a wavelength of 280 nm, and the peak position is not desirable as a blue fluorescent material. In addition, when the excitation wavelength is 457 nm, the peak position is shifted from 10 nm or more to a shorter wavelength as shown by the curve b in FIG. 1. This is considered to be due to the fact that the emission is caused only by Ce3 +. This indicates that there is a level other than the emission level that is considered to be directly attributable to Ce3 + due to contamination of impurities in the sample synthesized by the conventional method. FIG. 2 shows the reflection spectrum of SrS: Ce synthesized by the conventional method. An absorption peak that appears to be caused by Ce3 + is observed near 320 nm, but the reflectance is reduced over the entire visible range. That is, in this state, even if Ce3 + emits light, it cannot be taken out efficiently due to self-absorption. From the value of the band gap of SrS, it is considered that there is essentially no absorption in the visible region, and from this point, the existence of emission centers other than Ce3 + is inferred. As described above, in the conventional thin film EL material, when the material is used as the light emitting layer, a good thin film EL element cannot be obtained.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to provide a thin film EL material from which a highly efficient blue phosphor excellent in color purity and color coordinates can be obtained, and a thin film EL element using the material as a light emitting layer.
[0005]
[Means for Solving the Problems]
The above object is achieved by the following thin film EL material. That is, the present invention is strontium sulfide to which cerium is added, and when the reflectance at a wavelength of 420 nm is A and the reflectance at a wavelength of 320 nm is B, the following formula: A / B> 1.5 is satisfied, and At least one of the reflectance at a wavelength of 1000 nm exceeding 0.8, or the peak position of the emission spectrum does not change by 10 nm or more when excited with light having a wavelength of 280 nm and when excited with light having a wavelength of 450 nm. It is a thin film electroluminescent material characterized by satisfy | filling.
[0006]
The density | concentration of the cerium contained in SrS as a luminescent ion is 0.01-10 mol%, Preferably, it is 0.1-1 mol%. When the amount is 10 mol% or more, the luminance is significantly lowered due to concentration quenching, and when the amount is 0.01 mol% or less, sufficient luminance cannot be obtained. Further, when A / B ≦ 1.5, it is considered that the concentration of optically active Ce3 + dissolved in SrS is not sufficient, which is sufficient when the film is used as an EL device with a thin film. High brightness cannot be obtained. Further, when the reflectance at 1000 nm is smaller than 0.9, there are many optical centers other than Ce3 +, and the light emission of Ce3 + is absorbed, resulting in a decrease in luminous efficiency. SrS: Ce in the present invention can be obtained, for example, by the following method. That is, SrCO3 is obtained by firing several times in H2 S at a temperature of about 1000 to 1200 DEG C. before and after the addition of the Ce compound, and then finally firing at a temperature of about 1200 DEG C. in Ar or nitrogen gas. By performing this final baking, SrS: Ce having excellent color purity and high luminous efficiency can be obtained. The final firing atmosphere is not limited to Ar / nitrogen gas, and other inert gases may be used. Moreover, this invention is a thin film electroluminescent element using the thin film electroluminescent material of the said description for the light emitting layer.
[0007]
The thin film EL element of the present invention uses the above-described thin film material as a light emitting layer. An example showing the structure of such a thin film EL element is shown in FIG. In the figure, 1 is an upper electrode (back electrode) such as Al, 2 is an upper insulating layer, 3 is a buffer layer, 4 is a light emitting layer, 5 is a lower insulating layer, 6 is a lower electrode (transparent electrode) such as ITO, 7 is a glass substrate. The upper insulating layer 2 comprises a SiO2 layer 21 and a Si3 N4 layer 22, and the lower insulating layer 5 comprises a Si3 N4 layer 51 and a SiO2 layer 52.
[0008]
【Example】
Example 1
SrCO3 is used as a starting material and calcined in H2 S at 800 ° C. for 3 hours and then sieved. The sieved product is further calcined in H2 S at 1000 ° C. for 6 hours and sieved. To this, 0.1 mol% of Ce2 S3 and 0.2 mol% of KCl are added and mixed well, followed by baking in H2 S at 1180 ° C. for 4 hours and then sieving. The sieved product is further baked at 1180 ° C. for 4 hours in H 2 S and then sieved. The sieved product is further baked in H2 S at 1180 ° C. for 4 hours and then sieved. The sieved product is further fired at 1200 ° C. for 5 hours in Ar. FIG. 4 shows emission spectra at each stage after the third to fifth sulfurization. The emission intensity increases as the number of times of sulfiding increases, but at the same time, the peak position shifts to a longer wavelength, and the peak shape also changes from a double peak to a single peak.
A curve a in FIG. 5 shows an emission spectrum of a sample subjected to Ar treatment after the fifth sulfurization. The emission intensity increases, the peak position shifts to a short wavelength, and the peak shape changes to a double peak. FIG. 6 shows the reflection spectrum of this sample. In the sample after Ar treatment, the shape of the emission spectrum coincides with the shape of the emission spectrum of Ce3 +, and the reflection spectrum does not show any absorption other than the peak of Ce3 + in the visible range. It is considered that SrS: Ce is very little.
Further, the emission spectrum of a sample obtained by baking the Ar-treated sample again at 1180 ° C. in H 2 S for 4 hours is shown by a curve b in FIG. It can be seen that the peak position again moves to the long wavelength, the emission intensity decreases, and the peak shape becomes a single peak.
[0009]
Example 2
SrCO3 is used as a starting material and calcined in H2 S at 800 ° C. for 3 hours and then sieved. The sieved product is further calcined in H2 S at 1000 ° C. for 6 hours and sieved. To this, 0.1 mol% of Ce2 S3 and 0.2 mol% of KCl are added and mixed well, followed by baking in H2 S at 1180 ° C. for 4 hours and then sieving. The sieved product is further baked at 1180 ° C. for 4 hours in H 2 S and then sieved. The sieved product is further baked in H2 S at 1180 ° C. for 4 hours and then sieved. The sieved product is further calcined at 1200 ° C. for 5 hours in N2. The emission spectrum of SrS: Ce thus obtained is shown in FIG. 7, and the reflection spectrum is shown in FIG. After N2 treatment, the shape of the emission spectrum coincides with the shape of the emission spectrum of Ce3 +, and the reflection spectrum shows no absorption other than the peak of Ce3 + in the visible range. Is considered to be less SrS: Ce.
[0010]
Comparative Example 1
SrCO3 is used as a starting material and calcined in H2 S at 800 ° C. for 3 hours and then sieved. The sieved product is further calcined in H2 S at 1000 ° C. for 6 hours and sieved. Next, after baking at 1180 ° C. for 4 hours in H 2 S, sieving. The sieved product is further baked at 1180 ° C. for 4 hours in H 2 S and then sieved. The sieved product is further baked in H2 S at 1180 ° C. for 4 hours and then sieved. FIG. 9 shows the emission spectrum of the sample at each stage after the third, fourth and fifth sulfurization. In spite of no addition of cerium, an emission spectrum having a peak at 540 nm was obtained after the fourth sulfurization.
[0011]
It is surmised that the excessive S component in Examples 1 and 2 causes the long wavelength shift of the emission peak. This is supported by the fact that, in Comparative Example 1, emission of a peak at 540 nm is observed even without addition of cerium. The shape, position, and intensity of the emission spectrum changed by firing in Ar or N2 after high-order sulfidation, and S was desorbed from the composition part such as SrSX (x> 1), approaching stoichiometry. This is probably because optically active cerium increased. In the embodiment, KCl is added for charge compensation in addition to cerium, but lithium, sodium, rubidium, etc., which are monovalent cations, can also be used. It is also possible not to add at all.
[0012]
【The invention's effect】
When a thin film EL element using the thin film EL material of the present invention as a light emitting layer is used, a highly efficient blue phosphor excellent in color purity and color coordinates can be obtained.
[Brief description of the drawings]
1 is an emission spectrum; FIG. 2 is a reflection spectrum; and FIG. 3 is a schematic diagram showing the structure of a thin film EL element.
[Figure 4] Emission spectrum [Figure 5] Emission spectrum [Figure 6] Reflection spectrum [Figure 7] Emission spectrum [Figure 8] Emission spectrum [Figure 9] Emission spectrum

Claims (3)

Strontium sulfide added with cerium, where the reflectance at a wavelength of 420 nm is A and the reflectance at a wavelength of 320 nm is B, the following formula is satisfied: A / B> 1.5, and the reflectance at a wavelength of 1000 nm is It is characterized by satisfying at least one of exceeding 0.8, or when the peak position of the emission spectrum does not change by 10 nm or more when excited with light with a wavelength of 280 nm and when excited with light with a wavelength of 450 nm Thin film electroluminescent material. The thin film electroluminescent material according to claim 1, wherein the amount of cerium added is 0.01 to 10 mol%. A thin film electroluminescent device using the thin film electroluminescent material according to claim 1 as a light emitting layer.

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