JP6396260B2 - Vanadium oxide fluorescent powder and production method - Google Patents

Description

  The present invention relates to a vanadium oxide phosphor having high internal quantum efficiency that emits white light using ultraviolet / near ultraviolet light suitable as a light emitting material such as a white LED as excitation light, and a method for producing the same.

  In recent years, white LEDs are used in mobile phones and various display devices, and at the same time, are attracting attention as indoor lighting devices instead of fluorescent lamps from the viewpoint of energy saving. White LEDs use near-ultraviolet or blue LEDs as excitation light sources, and produce white light by combining phosphors having emission intensities at various wavelengths. Specifically, a blue LED emits yellow, green, and red phosphors as excitation light to obtain white light. (Patent Document 1)

However, the white LED white light obtained by combining a plurality of phosphors has problems such as color loss and strong light emission only at a specific wavelength, and efforts to improve color rendering properties when used as indoor lighting. Is required. For this reason, it is most desirable that the phosphor used in the white LED for illumination has a wide emission wavelength, does not have a sharp emission peak at a specific wavelength, and further exhibits white fluorescence with as few phosphor combinations as possible. In recent years, phosphors having a relatively wide emission wavelength such as α-sialon phosphors excited by blue LEDs (Patent Document 2) have been developed. However, since the emission spectrum range is not sufficiently wide, In addition, it was necessary to improve the color rendering properties in combination with some phosphors.
Thus, it was difficult to show white fluorescence with a color rendering property as good as possible with a single substance. As a result of intensive studies to solve such problems, the present inventors have found that vanadium oxide AVO ₃ (A is one or more selected from the group consisting of K, Rb, Cs, Li, It may contain one or more selected from the group consisting of Na and NH ₄ ), but exhibits a broad emission spectrum with a single substance, and has a fluorescence spectrum at a maximum around 500 to 540 nm by ultraviolet / near ultraviolet light excitation. It has been found that this phosphor emits white fluorescence broadly in the range of 400 to 800 nm, and is a particularly good phosphor that achieves an internal quantum efficiency of 87% at an excitation wavelength of 345 nm in CsVO ₃ (Non-patent Document 1). .

The fluorescent spectrum emitted from the phosphor of the present invention is an emission spectrum that is close to the spectrum of lighting fixtures currently used in consumer and ordinary fluorescent lamps. Since the spectrum peak is in the range of 500 to 540 nm, the color temperature is high, but it can also be combined with a phosphor having strong emission on the long wavelength side, and a warmer white color can be obtained, as well as mercury and Because it does not contain lead or the like, it has many advantages such as less adverse effects on the environment and human body, or it does not depend on rare resources because it does not contain rare earth ions. However, the vanadium oxide phosphor has a great influence on the properties of the phosphor from which the hygroscopicity of the raw material can be obtained in the production process, and it has been difficult to produce stably depending on the temperature and humidity of the synthesis work environment. Usually, a solid-phase reaction method is used in which vanadium oxide V ₂ O ₅ and alkali metal (A) carbonate A ₂ CO ₃ are mixed and baked. However, it is obtained depending on the season or weather that affects the synthesis work environment. It has been clarified that a large difference appears in the internal quantum efficiency of the fluorescent powder. For example, in the case of CsVO ₃ , variation was confirmed when the internal quantum efficiency (excitation wavelength: 345 nm) was in the range of 70% to less than 92%. Although a method of synthesizing at room temperature using moisture absorption of the raw material has been developed (Patent Document 3), it was confirmed that its internal quantum efficiency is not higher than that in the case of firing. In addition, CsVO ₃ to which Ge is added as a final product to suppress fluctuations in characteristics due to moisture absorption has been developed (Patent Document 4). However, fluctuations in characteristics due to uncertainties at the manufacturing stage are possible. Sex remained encapsulated. Since there was a problem in the stable supply of this material while having a substrate exhibiting extremely high luminous efficiency in this way, development of a method for obtaining high-quality AVO ₃ in a high yield was strongly desired. In addition to the problem of the manufacturing method, there was a problem that the excitation wavelength of this material system was largely deactivated from around 380 nm. Although AVO ₃ has a maximum internal quantum efficiency at an excitation wavelength near 350 nm, a near-ultraviolet LED of 385 nm to 405 nm is useful as a near-ultraviolet excitation light for illumination such as a general white LED. For this reason, there is a big problem that the strong fluorescence of AVO ₃ cannot be fully utilized. Therefore, the long wavelength shift of the excitation spectrum as a luminescent material (a significant improvement in internal quantum efficiency with respect to near-ultraviolet light from 385 nm to 405 nm) was also one of the important issues.

JP-A-11-31845 JP 2006-257326 A JP 2011-16670 A JP 2013-107947 A

Nature Materials 7 (2008) 735.

The present invention improves a large variation in characteristics (internal quantum efficiency under excitation light of 345 nm), which is a problem of the high-intensity white phosphor AVO ₃ , and is in addition to the near-ultraviolet excitation light region. It is an object to provide a fluorescent powder exhibiting high internal quantum efficiency and a method for producing the same.

The present inventor is able to produce a vanadium oxide fluorescent powder having an average primary particle size of 2 μm or more larger than the conventional one by a production method considering moisture addition in the course of proceeding tests and research under the above problems, A (A is an alkali metal that necessarily contains Cs, and may contain Li, Na, K, and Rb) and V and O, and A _d VO ₃ (d = 0.99 to 1.04) The vanadium oxide fluorescent powder having a composition ratio has an internal quantum efficiency of 90% or more under the excitation light of 345 nm with little variation, by setting the average primary particle diameter to 2 μm or more, and under the excitation light of 390 nm. It was found to have an internal quantum efficiency of 80% or more and 60% or more under 405 nm excitation light.

The present invention is based on such knowledge, and according to this application, the following invention is provided.
<1> A (A is an alkali metal that necessarily contains Cs, and may contain Li, Na, K, and Rb), V, and O, and A _d VO ₃ (d = 0.99 to 1) .04) having a compositional ratio of vanadium oxide and having an average primary particle diameter of 2 μm or more and exhibiting fluorescence emission in the entire range of 400 nm to 800 nm under blue to ultraviolet excitation light of 440 nm or less. Vanadium oxide fluorescent powder characterized by that.
<2> A ₂ CO ₃ and NH ₄ VO ₃ are mixed in a ratio of 1 + f (mol): 2 (mol) (f> 0) (A / V> 1), and 1 wt% or more of the mixed powder is H After adding ₂ O, the reaction powder obtained by drying at a temperature of 0 ° C. or more and less than 100 ° C. and then firing at a temperature of 400 ° C. or more and less than 500 ° C. is cooled to room temperature, and A: V = 1 The vanadium oxide fluorescence according to <1>, obtained by dissolving A ion (corresponding to f) added in excess of 1: 1 in water, washing, and baking again at a temperature of 400 ° C. or higher and lower than 500 ° C. Powder manufacturing method.

The vanadium oxide fluorescent powder of the present invention has an average primary particle diameter of 2 μm or more, the internal quantum efficiency under 345 nm excitation light is less than 90%, and has little variation, and under 390 nm excitation light. It has an internal quantum efficiency of 60% or more under excitation light of 80% or more and 405 nm. In addition, fluorescence is emitted over the entire range of 400 nm to 800 nm under blue to ultraviolet excitation light of 440 nm or less.
Further, when the production method of the present invention is used, the average primary particle diameter is 2 μm or more with high yield and the internal quantum efficiency under 345 nm excitation light is 90% or less, and there is little variation, and under the excitation light of 390 nm. An AVO ₃ powder having an internal quantum efficiency of 60% or more under an excitation light of 80% or more and 405 nm can be stably obtained.
If this fluorescent powder is used, it can also be used as a white LED using a near-ultraviolet LED of 385 nm to 405 nm as an excitation light source.

Excitation wavelength dependence of the internal quantum efficiency of CsVO ₃ obtained in Example 1 and Comparative Example 1 and increase in internal quantum efficiency from CsVO ₃ obtained by the conventional method (Comparative Example 5) of CsVO ₃ obtained in Example 1 (%). The SEM micrograph image and primary particle diameter of CsVO ₃ obtained in Example 1 and Comparative Example 5.

A (A is an alkali metal that necessarily contains Cs and may contain Li, Na, K, and Rb), V, and O, and A _d VO ₃ (d = 0.99 to 1.04) Vanadium oxide having an average compositional particle size of 2 μm or more, showing fluorescence emission in the entire range of 400 nm to 800 nm under blue to ultraviolet light of 440 nm or less, and 90 under excitation light of 345 nm. In order to obtain a fluorescent powder characterized by having a high internal quantum efficiency of at least%, A ₂ CO ₃ and NH ₄ VO ₃ are added to 1 + f (mol): 2 (mol) (f> 0) (A / V> 1) Mixing, adding 1 wt% or more of H ₂ O to the mixed powder, drying at a temperature of 0 ° C or more and less than 100 ° C, then firing at a temperature of 400 ° C or more and less than 500 ° C The reaction powder obtained is cooled to room temperature, and A: V 1: excessively added was A ions than 1 (f equivalent) was washed by dissolving in water, obtained by re-sintering at a temperature below 400 ° C. or higher 500 ° C..

Regarding the mixing of the raw material powder, the excess amount of A ₂ CO ₃ is f, but in order to make the mixed metal composition A / V> 1, f> 0 must be satisfied. There is no particular limitation on the upper limit of f for cleaning, but f is preferably about 0.05 to 0.15. The amount of water added to the mixed powder is effective if it is 1 wt% or more, but is preferably 10 wt% or more and 20 wt% or less in terms of handling. In the step of drying at a temperature of 0 ° C. or more and less than 100 ° C. after mixing the raw material powders, about 60 ° C. for about 2 hours is desirable. If there are many unreacted parts, recalcination may be performed at 300 ° C. or higher and lower than 400 ° C. Before recalcination, 1 wt% or more of H ₂ O may be added and mixed again. Even when the fluorescent powder obtained by firing is washed with excess A ions with water, the fluorescent powder is put into a sufficient amount of water at room temperature and stirred to collect the precipitated fluorescent powder. The fluorescent powder arranged above may be washed with water using an aspirator (or natural filtration) or the like. After washing with water, it is baked again at a temperature of 400 ° C. or higher and lower than 500 ° C. for drying and restructuring of the crystal surface. The average primary particle size is obtained by measuring and averaging the lengths in the long side direction of 40 primary particles randomly selected within an arbitrary visual field having a size of 20 μm × 20 μm square or more observed with an electron micrograph. . In order to distinguish it from aggregated secondary particles, a particle size distribution measuring instrument using light scattering / diffraction is not used. Fluorescence internal quantum efficiency is calculated by using [integral quantum efficiency] = Nem / Nabs × 100 (Nem is the number of emitted photons, and Nabs is the number of absorbed photons) using an integrating sphere, a light receiving element (CCD is desirable) and a spectral excitation light source. .

The vanadium oxide fluorescent powder represented by A _d VO ₃ (d = 0.99 to 1.04) obtained in the present invention has a wavelength of 250 to 410 nm that can be excited by an ultraviolet / near ultraviolet LED that is an excitation light source of a white LED. Has a strong excitation spectrum in the range. Compared with the conventional fluorescent powder having the same chemical composition, the emission intensity in the near ultraviolet region (internal quantum efficiency: FIG. 1) is greatly improved by about 380 to 410 nm, which is difficult with the conventional fluorescent powder having the same composition. A near ultraviolet LED of ˜405 nm can be used as an excitation light source. The fluorescence spectrum emitted by this excitation light extends from 400 to 800 nm and emits white light. Therefore, it is suitable as a phosphor for white LED. Since this fluorescent powder does not contain mercury or lead, it has little adverse effect on the environment and human body. Therefore, the vanadium oxide fluorescent powder of the present invention is extremely useful for white LEDs, and can be used as lighting devices such as daily lights and display devices such as backlights used in various display devices.

The vanadium oxide fluorescent powder of the present invention is preferably composed of only the elements contained in the above composition formula, but the range in which the internal quantum efficiency is not significantly reduced (for example, within 5.0 atomic%, preferably 1.0). It is allowed to contain other elements (for example, Ge, Mg, Ca, Sr, Ba, Zn, NH _4, etc.) within the atomic percent, more preferably within the range of 0.1 atomic percent.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to this Example, A material change, a setting adjustment, etc. are possible suitably in the range which does not deviate from the summary of this invention. The fluorescence internal quantum efficiency was measured using an absolute PL quantum yield measuring device C9920-02 manufactured by Hamamatsu Photonics.

Example 1
CsVO ₃ was synthesized using a solid phase method. Cs ₂ CO ₃ and NH ₄ VO ₃ were used as starting materials for Cs and V, respectively, and weighed so that the composition ratio was Cs / V = 1.1, and 15 wt% water was added to the total amount and mixed. Then, after leaving at room temperature (20 degreeC) for 1 hour, it dried at 60 degreeC for 2 hours, and calcined at 350 degreeC for 12 hours. After taking out to room temperature, 15 wt% water was added and mixed again, and it was calcined again at 350 ° C. for 12 hours. Then, it heated up to 450 degreeC and baked for 12 hours, and reaction was advanced. The obtained CsVO ₃ was washed with water, and excess Cs was dissolved in water and removed. Thereafter, the temperature was once again raised to 450 ° C. and baked for 12 hours to complete the reaction. The obtained CsVO ₃ fluorescent powder has an average primary particle size of 4 μm (see FIGS. 2B and 2C), and has a strong excitation spectrum in the range of 250 to 410 nm that can be excited by ultraviolet / near ultraviolet LEDs. In addition, the emission intensity (internal quantum efficiency) in the near ultraviolet region of about 380 to 410 nm was significantly improved as compared with the conventional fluorescent powder having the same chemical composition (see FIG. 1). Also, it emits fluorescence in the entire range of 400 nm to 800 nm under blue to ultraviolet light of 440 nm or less, shows 95.8% under excitation light of 345 nm, 88% or more under excitation light of 390 nm, and under excitation light of 405 nm. It was confirmed that the internal quantum efficiency was 81% or higher.

Example 2
When synthesis was performed 10 times by the same production method of Example 1, the fluorescent powders of all synthesis examples had an average particle diameter of more than 2 μm, and the average value of internal quantum efficiency measured under 345 nm excitation light. Was 92.3%, the lowest value was 90.1%, and the highest value was 95.8%. In addition, it emits fluorescence over the entire range from 400 nm to 800 nm under blue to ultraviolet light of 440 nm or less, and has an internal quantum efficiency of 80% or more under excitation light of 390 nm and 60% or more under excitation light of 405 nm. Confirmed that.

Example 3
CsVO ₃ was synthesized using a solid phase method. Using Cs ₂ CO ₃ and NH ₄ VO ₃ as starting materials for Cs and V, respectively, weighed so that the composition ratio of Cs / V = 1.05 was obtained, and 15 wt% water was added to the total amount and mixed. Then, after leaving at room temperature (20 degreeC) for 1 hour, it dried at 60 degreeC for 2 hours, and calcined at 350 degreeC for 12 hours. After taking out to room temperature, 15 wt% water was added and mixed again, and it was calcined again at 350 ° C. for 12 hours. Then, it heated up to 450 degreeC and baked for 12 hours, and reaction was advanced. The obtained CsVO ₃ was washed with water, and excess Cs was dissolved in water and removed. Thereafter, the temperature was once again raised to 450 ° C. and baked for 12 hours to complete the reaction. The obtained CsVO ₃ fluorescent powder has an average primary particle size of 4 μm, exhibits fluorescence emission in the entire range of 400 nm to 800 nm under blue to ultraviolet light of 440 nm or less, and 92% or more under excitation light of 345 nm. It was confirmed that the internal quantum efficiency was 80% or more under excitation light of 390 nm and 60% or more under excitation light of 405 nm.

Example 4
CsVO ₃ was synthesized using a solid phase method. Cs ₂ CO ₃ and NH ₄ VO ₃ were used as starting materials for Cs and V, respectively, and weighed so that the composition ratio was Cs / V = 1.5, and 15 wt% water was added to the total amount and mixed. Then, after leaving at room temperature (20 degreeC) for 1 hour, it dried at 60 degreeC for 2 hours, and calcined at 350 degreeC for 12 hours. After taking out to room temperature, 15 wt% water was added and mixed again, and it was calcined again at 350 ° C. for 12 hours. Then, it heated up to 450 degreeC and baked for 12 hours, and reaction was advanced. The obtained CsVO ₃ was washed with water, and excess Cs was dissolved in water and removed. Thereafter, the temperature was once again raised to 450 ° C. and baked for 12 hours to complete the reaction. The obtained CsVO ₃ fluorescent powder has an average primary particle size of 4 μm, exhibits fluorescence emission in the entire range of 400 nm to 800 nm under blue to ultraviolet light of 440 nm or less, and 92% or more under excitation light of 345 nm. It was confirmed that the internal quantum efficiency was 80% or more under excitation light of 390 nm and 60% or more under excitation light of 405 nm.

Example 5
A rare earth-free white LED was produced by kneading the CsVO ₃ fluorescent powder produced by the method shown in Example 1 with a silicone resin and immobilizing it on a 385 nm near-ultraviolet LED. The produced white LED showed white light expressed by (0.32, 0.42) on the CIE chromaticity coordinates, and the color temperature was 6028K.

Comparative Example 1
A synthesis aimed at CsVO ₃ was performed using a solid phase method. Cs ₂ CO ₃ and NH ₄ VO ₃ were used as starting materials for Cs and V, respectively, and weighed so that the composition ratio was Cs / V = 1.0, and 15 wt% water was added to the total amount and mixed. Then, after leaving at room temperature (20 degreeC) for 1 hour, it dried at 60 degreeC for 2 hours, and calcined at 350 degreeC for 12 hours. After taking out to room temperature, 15 wt% water was added and mixed again, and it was calcined again at 350 ° C. for 12 hours. Then, it heated up to 450 degreeC and baked for 12 hours, and reaction was advanced. The obtained powder was out of the composition range of the present invention, an orange impurity phase considered to be V ₂ O ₅ was often observed, and high quantum efficiency was not obtained.

Comparative Example 2
CsVO ₃ was synthesized using a solid phase method. Cs ₂ CO ₃ and V ₂ O ₅ were used as starting materials for Cs and V, respectively, and weighed so that the composition ratio was Cs / V = 1.05, and 15 wt% water was added to the total amount and mixed. Then, after leaving at room temperature (20 degreeC) for 1 hour, it dried at 60 degreeC for 2 hours, and calcined at 350 degreeC for 12 hours. After taking out to room temperature, 15 wt% water was added and mixed again, and it was calcined again at 350 ° C. for 12 hours. Then, it heated up to 450 degreeC and baked for 12 hours, and reaction was advanced. Although the obtained powder was identified as CsVO ₃ , the average primary particle size was less than 2 μm, and high quantum efficiency exceeding 90% was not obtained under excitation light of 345 nm.

Comparative Example 3
CsVO ₃ was synthesized using a solid phase method. Using Cs ₂ CO ₃ and NH ₄ VO ₃ as starting materials for Cs and V, respectively, weighed so that the composition ratio of Cs / V = 1.0, and calcined at 350 ° C. for 12 hours without adding water. went. After taking out to room temperature, it mixed well again, heated up to 450 degreeC, baked for 12 hours, and reaction was advanced. Although the obtained powder was identified as CsVO ₃ , the average primary particle size was less than 2 μm, and high quantum efficiency exceeding 90% was not obtained under excitation light of 345 nm.

Comparative Example 4
A synthesis aimed at CsVO ₃ was performed using a solid phase method. Cs ₂ CO ₃ and NH ₄ VO ₃ were used as starting materials for Cs and V, respectively, and weighed so that the composition ratio was Cs / V = 1.0, and 15 wt% water was added to the total amount and mixed. Then, after leaving at room temperature (20 degreeC) for 1 hour, it dried at 60 degreeC for 2 hours, and calcined at 350 degreeC for 12 hours. After taking out to room temperature, 15 wt% water was added and mixed again, and it was calcined again at 350 ° C. for 12 hours. Then, it heated up to 450 degreeC and baked for 12 hours, and reaction was advanced. Thereafter, the powder obtained without washing with water was out of the composition range of the present invention, and its quantum efficiency was measured under excitation light of 345 nm, but a high quantum efficiency exceeding 90% was obtained. I couldn't.

Comparative Example 5
CsVO ₃ was synthesized using a solid phase method. Using Cs ₂ CO ₃ and V ₂ O ₅ as starting materials for Cs and V, respectively, weighed so that the composition ratio of Cs / V = 1.05, and calcined at 350 ° C. for 24 hours without adding water. went. After taking out to room temperature, it mixed well again, heated up to 450 degreeC, baked for 24 hours, and reaction was advanced. Although the obtained powder was identified as CsVO ₃ , synthesis was carried out 10 times by the same production method. In all synthesis examples, the average primary particle diameter was less than 2 μm and the internal quantum measured under excitation light of 345 nm. The average value of efficiency was 84.4%, and a high quantum efficiency exceeding 92% was not obtained. One of the 10 syntheses was 91.6%, but excluding it, all were less than 90% and the lowest value was 71.8%.

  If the material of this invention is used, it has a strong excitation spectrum in the range of 250-410 nm which can be excited by ultraviolet and near ultraviolet LED which is an excitation light source of white LED. Compared with the conventional fluorescent powder having the same chemical composition, the emission intensity in the near ultraviolet region (internal quantum efficiency: FIG. 1) is greatly improved by about 380 to 410 nm. A near-ultraviolet LED of ˜405 nm can be used as an excitation light source. The fluorescence spectrum emitted by this excitation light extends from 400 to 800 nm and emits white light. Therefore, it is suitable as a phosphor for white LED. Since this fluorescent powder does not contain mercury or lead, it has little adverse effect on the environment and human body. Therefore, the vanadium oxide fluorescent powder of the present invention is extremely useful as a white LED, and can be used as a lighting device such as a daily light or a display device such as a backlight used in various display devices.

Claims (2)

A (A is an alkali metal that necessarily contains Cs and may contain Li, Na, K, and Rb), V, and O, and A _d VO ₃ (d = 0.99 to 1.04) Vanadium oxide fluorescent powder having a compositional ratio of 1 to 2, characterized in that the average primary particle diameter is 2 μm or more, and exhibits fluorescence emission in the entire range of 400 nm to 800 nm under blue to ultraviolet light of 440 nm or less. Vanadium oxide fluorescent powder. A ₂ CO ₃ and NH ₄ VO ₃ are mixed in a ratio of 1 + f (mol): 2 (mol) (f> 0) (A / V> 1), and 1 wt% or more of H ₂ O is added to the mixed powder. After the addition, the reaction powder obtained by drying at a temperature of 0 ° C. or more and less than 100 ° C. and then firing at a temperature of 400 ° C. or more and less than 500 ° C. is cooled to room temperature, and A: V = 1: 1 The vanadium oxide fluorescent powder according to claim 1 obtained by dissolving excessively added A ions (corresponding to f) in water, washing, and firing again at a temperature of 400 ° C or higher and lower than 500 ° C. Production method.

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