JP5014112B2 - Electroluminescent phosphor, electroluminescent device, and sputtering target for producing the same - Google Patents

Description

  The present invention relates to a ZnS-based electroluminescent phosphor used for in-vehicle display devices, information equipment displays, phosphor sensors, and the like. Furthermore, this invention also provides the electroluminescent element containing the said fluorescent substance, and the sputtering target for manufacturing the said fluorescent substance.

  Electroluminescence (hereinafter sometimes abbreviated as “EL”) is a phenomenon in which a phosphor is excited by an electric field and emits excitation energy as light of a specific wavelength. A display using this EL (EL display) is attracting attention as a display using a self-luminous substance that does not require a backlight unlike a liquid crystal. Examples of the phosphor used in the EL display include inorganic phosphors and organic phosphors.

  As the inorganic phosphor, a ZnS phosphor is widely used. This is because ZnS is one of direct transition type compound semiconductors, is transparent to light in the visible light region, and can easily form a light-emitting recombination center with high emission efficiency by adding an appropriate impurity. ZnS phosphors are roughly classified into powder phosphors and thin film inorganic phosphors depending on the manufacturing method.

  Examples of the former powder-type phosphor include ZnS-based phosphors in which Cu, Cl, Al, Ag, or the like is added to ZnS (see Patent Documents 1 and 2), and ZnS-Cu-Cl phosphors are mainly used. It is. This phosphor is manufactured by adding 1% by mass or less of Cu and Cl to ZnS and then heat-treating at 1000 ° C. or higher, and emits green fluorescence when irradiated with ultraviolet light having a wavelength of around 365 nm. It has been known. For the EL element, a powder type ZnS—CuCl phosphor of about 10 to 100 μm is used. However, an EL element using a powder-type phosphor has a defect that uneven display tends to occur.

On the other hand, as the latter thin film type phosphor, a ZnS-Mn phosphor is representative. It is known that a thin-film type ZnS-Mn phosphor is mainly formed by vacuum deposition or sputtering (see, for example, Patent Documents 3 and 4) and exhibits orange fluorescence. In particular, a thin film type phosphor formed by a sputtering method has an advantage that a composition almost the same as the component composition of the sputtering target is obtained and display unevenness is small. However, the brightness of the thin film type ZnS-Mn phosphor is slightly inferior to that of the powder type phosphor. In particular, a thin film type ZnS-Mn phosphor formed by sputtering has a drawback that good luminance cannot be obtained.
JP 2006-52250 A JP 2005-126465 A JP 2006-511046 A Japanese Patent Laid-Open No. 8-96966

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a thin-film electroluminescent phosphor and an electroluminescent element having high luminous efficiency and high luminance, and a sputtering target for producing them. It is to provide.

  The electroluminescent phosphor of the present invention that has achieved the above-described problem is an electroluminescent phosphor comprising a ZnS-based film containing Mn, further containing B, and Mn from 0.2 to the total mass of ZnS. 2% by mass and 0.001 to 0.30% by mass of B are contained.

  In the present invention, the mass ratio (B / Mn) between B and Mn is preferably less than 1.

  The phosphor of the present invention is preferably a thin film phosphor having a film thickness of 10 nm to 5000 nm, and more preferably formed by sputtering.

  The present invention also includes an electroluminescence element including the phosphor.

  The sputtering target of the present invention that has achieved the above-mentioned problems is a target for producing the above-described electroluminescent phosphor, and is 0.2 to 2% by mass of Mn and 0.2% by mass with respect to the total mass of ZnS. It is made of a ZnS-based alloy containing 001 to 0.30 mass% B.

  Since the electroluminescent phosphor of the present invention is composed of a ZnS-based thin film containing a predetermined amount of both Mn and B in ZnS as a base material, it can exhibit high luminance. According to the present invention, sufficient brightness is exhibited even when a film is formed by a sputtering method, so that it is suitably used for manufacturing a large display or the like as a dense thin film phosphor for a large area with excellent component uniformity. .

  The electroluminescent phosphor (EL phosphor) of the present invention is characterized in that it contains a predetermined amount of B (boron) in a conventional ZnS-Mn thin film containing Mn in ZnS. According to the examination results of the present inventors, it has been found that when B is added to ZnS—Mn, higher luminance can be obtained than when B is not added. In addition, it has been found that the brightness enhancement effect due to the addition of B is not exhibited even when added to ZnS, but is remarkably exhibited when added to ZnS-Mn containing Mn, thereby completing the present invention.

(EL phosphor)
The ZnS-Mn-B phosphor of the present invention contains 0.2 to 2% by mass of Mn and 0.001 to 0.30% by mass of B with respect to the total mass of ZnS. The phosphor of the present invention exhibits orange fluorescence, which is considered to originate from the inner shell transition of Mn.

  First, Mn is contained in the range of 0.2 to 2% by mass with respect to the total mass of ZnS. Mn is a component that is usually added as an activator that promotes light emission of the ZnS-based phosphor, and the lower limit of the amount of Mn is 0.2% by mass in order to obtain high emission luminance. However, if the amount of Mn becomes excessive, the phosphor itself is colored and the amount of light emission to be observed decreases, so the upper limit is made 2 mass%. A preferable amount of Mn is 0.3% by mass or more and 1.5% by mass or less, and more preferably 0.5% by mass or more and 0.8% by mass or less.

  B is a component that characterizes the present invention. So far, no example of adding B to a ZnS-Mn EL phosphor has been known. As shown in the examples to be described later, B itself does not emit light, but ZnS-Mn-B in which B is added to a ZnS-Mn phosphor is fluorescent compared to a conventional ZnS-Mn phosphor that does not contain B. Became stronger, and light emission was observed from the entire surface of the phosphor. From this, it is inferred that B has a “fluorescence promoting action” that enhances fluorescence by repairing defects in ZnS that hinder fluorescence. Such an action of B is effectively exhibited by adding 0.001% by mass or more (preferably 0.01% by mass or more, more preferably 0.03% by mass or more) with respect to the total mass of ZnS. . However, if the amount of B is excessive, the fluorescence is weakened and light is emitted only on the side surface of the substrate end. Therefore, the B amount is determined to be 0.30% by mass or less (preferably 0.20% by mass or less, more preferably 0.15% by mass or less) with respect to the total mass of ZnS.

  In the ZnS-Mn-B phosphor of the present invention, the mass ratio (B / Mn) between B and Mn is less than 1, in other words, the B content is preferably less than Mn. When the content of B is the same as Mn or more than Mn, B does not function as the “fluorescence promoting element” described above, but instead acts as an “impurity element” that weakens the fluorescence. is there. In order to effectively exhibit the fluorescence promoting action by addition of B, the B / Mn ratio is preferably as small as possible. For example, it is more preferably 0.9 or less, and even more preferably 0.7 or less. The lower limit of the ratio of B / Mn is not particularly limited, but is generally preferably 0.01.

  The EL phosphor of the present invention contains Mn and B in the above range, and the balance is substantially ZnS. However, the phosphor of the present invention may contain unavoidable impurities which are mixed depending on manufacturing conditions and the like.

  Here, the ratio of S to the total amount of Zn and S does not need to be strictly 0.5 (that is, Zn: S = 1: 1) in ZnS as a base material component, and generally 0.45 to It is preferable to be within the range of 0.28. As will be described later, the ZnS-Mn-B thin film constituting the phosphor of the present invention is preferably formed by a sputtering method, but ZnS is easily decomposed during film formation, and the S component is reduced by evaporation. Tend to. Therefore, the ratio of Zn and S in the thin film formed by the sputtering method is not strictly 1: 1, and the ratio of S is reduced. It has been confirmed that there will be no impact.

  The EL phosphor of the present invention can exhibit sufficient fluorescence even if it is a thin film type, particularly a film formed by sputtering. In order to ensure sufficient fluorescence, the thickness of the phosphor is preferably as thick as possible, preferably 10 nm or more, more preferably 100 nm or more, and even more preferably 300 nm or more. However, when the phosphor film becomes thick, unevenness in light emission may occur due to surface roughness. Further, if the film thickness becomes too thick, the internal stress increases, the thin film phosphor is cracked, and may be peeled off from the substrate or the like. The upper limit of the phosphor film thickness is preferably 5000 nm, more preferably 2000 nm, and even more preferably 1500 nm.

(Method for producing EL phosphor)
Next, the manufacturing method of the ZnS-Mn-B thin film which comprises EL fluorescent substance concerning this invention is demonstrated. The thin film can be formed by a physical vapor deposition method such as a sputtering method or a vacuum vapor deposition method, but it is particularly preferable to form the film by a sputtering method. Among sputtering, the RF magnetron sputtering method is recommended.

  The sputtering method is a method in which a plasma discharge is formed between a substrate and a sputtering target (target material) made of the same material as the thin film material, and a gas ionized by the plasma discharge is collided with the target material. This is a method for producing a thin film by knocking out atoms of a material and depositing them on a substrate. Unlike the vacuum evaporation method, the sputtering method has an advantage that a thin film having almost the same composition as the target material can be formed.

  Hereinafter, a preferred method for producing a sputtering target (powder sintering method) used in the present invention will be described.

  First, powders of ZnS, Mn, and B as raw materials are prepared, and a mixture in which the contents of Mn and B are appropriately controlled with respect to ZnS is prepared. The amount of Mn and B added to ZnS is the same as that of the thin film described above, and the amount of Mn is 0.2% by mass or more (preferably 0.3% by mass or more, more preferably 0.5% by mass) with respect to ZnS. % Or more), 2 mass% or less (preferably 1.5 mass% or less, more preferably 0.8 mass% or less), and the B content is 0.001 mass% or more (preferably 0.01 mass% or more, more Preferably it is 0.03 mass% or more), 0.30 mass% or less (preferably 0.20 mass% or less, more preferably 0.15 mass% or less).

  The mixing apparatus used for this invention is not limited, For example, well-known mixing apparatuses, such as a ball mill, a rod mill, and a V-type mixer, can be used. What is necessary is just to adjust mixing time suitably according to the quantity etc. of a mixture so that a mixture can be mixed uniformly.

Next, the mixture is molded using, for example, a 1 t / cm ² mold press molding machine to obtain a molded product having a thickness of about 5 to 10 mm, and then sintered to obtain a target. Sintering conditions are not particularly limited, and for example, it is preferably performed at about 850 to 1300 ° C. for about 1 to 5 hours in an inert gas (Ar, N _2, etc.) atmosphere.

  The sputtering target thus obtained has substantially the same composition as the EL phosphor made of the ZnS—Mn—B thin film.

Next, a ZnS—Mn—B thin film is formed by sputtering using the above sputtering target. The details of the sputtering method are not particularly limited. For example, a commonly used sputtering method such as a DC sputtering method, an RF magnetron sputtering method, or a reactive sputtering method can be employed. Preferred conditions for depositing the thin film of the present invention by RF magnetron sputtering are as follows:
Substrate temperature: 300 ° C. to room temperature Sputtering gas: Ar
Gas pressure: 2 to 10 mTorr
Applied power: 1 to 10 W / cm ²

(EL element and manufacturing method thereof)
The present invention also includes an EL element including the above thin film phosphor. The EL element has a sandwich structure in which both sides of the thin film phosphor layer (light emitting layer) are sandwiched between electrodes (cathode, anode), and the sandwich structure is formed on a substrate. As the configuration and manufacturing method of the EL element of the present invention, for example, conventionally known ones described in Patent Documents 1 to 4 described above can be adopted.

  As described above, in the present invention, it is preferable to form the light emitting layer by sputtering, but the heating condition after the film formation is an inert atmosphere (for example, a vacuum atmosphere or an inert gas atmosphere such as Ar, preferably Is preferably performed in a vacuum atmosphere). For example, after sputtering, it is recommended to perform heat treatment at 200 to 500 ° C. (preferably 300 to 450 ° C.) for 10 to 120 minutes (preferably 30 to 60 minutes) in a vacuum atmosphere.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples, and appropriate modifications are made within a range that can meet the above and the following purposes. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

Example 1
In this example, various thin film samples having different amounts of Mn and B were prepared, and the fluorescent state was compared by irradiating with black light.

  Specifically, ZnS powder, metal Mn, and simple substance B as raw materials were prepared and mixed at the ratios shown in Table 1. For comparison, examples including no Mn and B, examples including only Mn, and examples including only B were also prepared.

  Next, the above mixture is molded with a mold press molding machine to obtain a molded body having a thickness of 7 mm, and then fired at 1000 ° C. for 2 hours in an Ar atmosphere to obtain a round sputtering target having a diameter of 30 cm. Manufactured.

Using the sputtering target thus obtained, a thin film was formed on a glass substrate (Corning Corporation: # 1737) by magnetron sputtering (sputtering gas: Ar, gas pressure: 2 mTorr, RF discharge, applied power: 2 W / cm ² ). A film was formed. The film thickness was adjusted by controlling the sputtering time within the range of 90 seconds to 30 minutes. Next, the substrate on which the thin film was formed was heat-treated at 300 ° C. for 30 minutes in a vacuum atmosphere, and the composition after the heating was analyzed by an ICP method. Table 1 shows the composition of the thin film sample after heating (the amounts of Mn and B with respect to ZnS and the ratio of S / (ZnS + S)) and the film thickness.

(Fluorescence characteristic evaluation)
The obtained thin film sample was irradiated with black light (maximum intensity wavelength: 352 nm) containing ultraviolet rays having a wavelength of 340 nm to 350 nm, and the presence or absence of fluorescence was visually observed. The fluorescence state was evaluated by comparison with 2 (conventional ZnS-Mn thin film phosphor not containing B). The evaluation criteria are as follows. In addition to the fluorescent state, display unevenness, peeling and coloring were also observed.
◎: Bright overall light emission ○: Slightly bright overall light emission △: Light emission only at the edge of the glass substrate ×: No light emission

  These results are shown in Table 1.

  No. containing only ZnS. 1 and No. 1 containing no Mn. With 3 (ZnS-0.1 mass% B), no luminescence was confirmed. In addition, the conventional example No. In 2 (ZnS-0.5 mass% Mn), light was emitted only at the end of the side surface of the glass substrate.

  On the other hand, No. containing both Mn and B within the scope of the present invention. Nos. 4 to 8 and 10 to 13 showed a good fluorescent state, no display unevenness or peeling, and good coloring. On the other hand, no. No. 9 emits light only at the end of the side surface of the substrate, while No. 9 having an excessive amount of Mn. In No. 16, the phosphor itself was colored and the light emission was weak. In addition, No. with a thick film thickness. Although 15 emitted light, many peeling occurred. No. In No. 14, dot-like display unevenness occurred because the film thickness was large.

  The effect of addition of B is particularly No. It is clear when 2, 4-9 are compared. These are examples of thin films (thickness 600 nm) containing Zn content in the range of 0.01 to 0.35 mass% in ZnS-0.5 mass% Mn. No. 2 containing B in the scope of the present invention compared to No. 2. 4-8 have shown the favorable fluorescence state. Moreover, the B amount exceeds the range of the present invention. In 9, the fluorescence state decreased. When the content of B and the fluorescent state are examined, the fluorescent state tends to become better as the B content increases, and is saturated at about 0.04% by mass (No. 5). When the amount was about 20% by mass (No. 8), a tendency to decrease was observed.

Example 2
In this example, in order to investigate the light emission promoting effect by addition of B, a ZnS-Mn-B thin film (No. 4 in Table 1) containing B within the scope of the present invention and ZnS which is a conventional example not containing B are used. Using a —Mn thin film (No. 2 in Table 1), the fluorescence characteristics were measured by cathodoluminescence (CL) measurement.

  Specifically, CL measurement was performed using each of the above thin film samples (all film thicknesses were 600 nm), and the number of CL photons per 1 s was counted. CL was measured by electron current: 0.3 nA, measurement time: 500 ms, and an emission wavelength between 300 nm and 800 nm at 1 nm intervals. These results are shown in FIG.

  As shown in FIG. 1, No. 1 containing B within the scope of the present invention. No. 4 contains no B. Compared to 2, the CL strength was 10 times higher. However, these maximum emission wavelengths are almost the same. 2 589 nm, No. 2 4 was 592 nm. From these experimental results, it was confirmed that B does not emit light itself but has a light emission promoting action for promoting light emission of Mn.

No. in Table 1 2 (without B) and No. 2 It is a graph which shows the result of the cathode luminescence (CL) measurement of 4 (invention example).

Claims (5)

In an electroluminescent phosphor composed of a ZnS-based film containing Mn,
The ZnS-based film further contains B,
Containing 0.2 to 2% by mass of Mn and 0.001 to 0.30% by mass of B with respect to the total mass of ZnS ,
An electroluminescent phosphor formed by sputtering .   2. The electroluminescent phosphor according to claim 1, wherein a mass ratio (B / Mn) of B and Mn is less than 1. 3.   The electroluminescent phosphor according to claim 1 or 2, wherein the film thickness is 10 nm or more and 5000 nm or less. The electroluminescent element containing the electroluminescent fluorescent substance in any one of Claims 1-3 .   A sputtering target comprising a ZnS-based alloy containing 0.2 to 2% by mass of Mn and 0.001 to 0.30% by mass of B with respect to the total mass of ZnS.

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