TWI474967B - Improvements to phosphors - Google Patents

Description

Improvements in phosphors

A first aspect of the invention relates to a solution for improving the properties of a phosphor, and a second aspect relates to the use of a phosphor to convert UV-visible light, in particular ultraviolet (UV) or blue light, into light suitable for use herein. Electroluminescent device.

While the primary industrial application of the present invention resides in a device that is based on conversion to white light, it can be advantageously used if the transformation of interest is selected from a narrow band of rays (i.e., colored rays) of the visible spectrum.

Phosphors for converting UV light are used in a wide variety of devices, the most common of which are discharge lamps, fluorescent lamps, phosphor white LEDs, and displays for viewing information (especially plasma displays).

One of the problems faced by phosphors is that they may decompose due to the action of H ₂ O in the same device as used. Further information on the effect of H ₂ O on phosphors can be found in the paper "Investigation on fluorescence degradation mechanism of hydrated BaMgAl ₁₀ :Eu ²⁺ phosphor" by Mishra et al., published in Electrochemical Society, No. 152, p. 183-190. To solve this problem, the use of zeolite as a phosphor is described in the patent application published in JP 2008069290, wherein the fluorescent matrix is subjected to ion exchanged zeolite with rare earth ions derived from a salt solution. In this patent application, since the description of the fluorescent nano zeolite (i.e., zeolite particles having a nanometer size in a single direction) is not effective in the emission of light rays, the zeolite crystallizes into a hexagonal plate shape. Furthermore, the patent application JP2008069290 requires that the ion exchange rate of the zeolite be at least 20%.

International Patent Application WO 2009/123498 addresses the problem of phosphor decomposition by the application of zeolite and nanostructured metal oxides, and Guochofeng et al., "Study on the stability of phosphor SrAl ₂ O ₄ , Eu ²⁺ , Dy ^{3 +} , in water and method to improve its moisture resistance", published in 2007 by Material Chemistry and Physics, No. 106, p. 268-272 suggests coating the phosphor with an insulating material.

Instead, the use of a nanostructured H ₂ O in an electroluminescent organic device is disclosed in the published patent application EP 1 655 792, which describes the use of a light-transmissive layer to remove H ₂ O from a metal salt having a size below 100 nm or oxidized. The composition of the object to ensure its light transmission.

The object of the present invention is to improve the properties of a phosphor which not only faces the decomposition problem due to the presence of H ₂ O but also improves the quality by improving the radiation emitted by the phosphor, and in its first aspect, relates to a use To convert a ray (in the most common case, a wavelength in the range of 210 nm to 800 nm) into a composite layer of visible light comprising a layer of phosphor combined with a nano-sized zeolite characterized by 95% of these nanoparticles The size of the zeolite is between 60 and 400 nm.

In general, when describing a reference particle size, it will mean that at least 95% of the particles are included within the specified size range.

In particular, the inventors have found that by using a particular type of H ₂ O absorber having a specified (nano) particle size, i.e., zeolite, not only extends its lifetime, but also improves the emission properties of the phosphor.

It is important that most of the zeolites have a specified size and that a small fraction (less than 5%) of the acceptable size is outside the specified range (ie, 60-400 nm).

Regarding the method of use thereof, the nano zeolite can be obtained by a suitable dispersing agent (such as water, methanol, isopropanol, ethyl cellulose, n-butanol, xylene, hydroxypropylmethylcellulose, polyvinylpyrrolidone, Polyvinyl methyl ether, polyacrylic acid, polyethylene oxide, which are all removed after curing by curing treatment. Alternatively, the nano zeolite can be used in a form that is dispersed in a polymeric matrix (which must be transparent, the incident light transmittance of the substrate is at least 90%, and must also ensure light transmission in the UV range). In this case, it is preferred to use a polydialkyl decane resin. Alternatively, the nano zeolite may also be dispersed by an inorganic binder such as alumina or alumina coated cerium oxide spheres.

In particular, three possible preferred embodiments were found, each of which provides a particular advantage.

According to their first, the zeolite is mixed with the phosphor; in this case, an improvement in the uniformity of luminescence and a slight increase thereof are observed. In this embodiment, the preferred size of the nano zeolite is between 80 and 150 nm and the particle distribution peak is at about 100 nm (i.e., 95% zeolite is in the range of 90-110 nm) to give the best results.

According to a second embodiment, the nano zeolite forms a coating overlying the phosphor such that the coating faces the interior of the device.

In a device in which mercury is present, such as a fluorescent lamp, this particular configuration is particularly advantageous because of the protective effect of nano zeolite on H ₂ O and mercury vapor which also causes decomposition of the phosphor, such as a patent application. As shown in US 2009/0050848, it discloses a protective layer, but does not take into account the effect on particle size selection used to form this layer.

Therefore, the use of the nano zeolite according to the present invention also has an additional effect of reducing mercury consumption due to the presence of water and its decomposition products (OH ⁺ and H ^- radicals). This mechanism of action between mercury and water and its derivatives, such as the paper "The effect of contaminants on the mercury consumption of fluorescent lamps", I. Bakk et al., J. Phys. D: Appl. Phys. 42 (2009) 095501, not only includes the necessity of using a higher amount of Hg which is not desired, but also reduces the luminous intensity compared to the initial value. According to the invention, in this embodiment, the preferred size of the nano zeolite is between 250 and 350 nm. In particular, the particle distribution peak is located at about 300 nm, i.e., 95% of the nano zeolite is in the range of 280-320 nm, and the best results are obtained.

The third variant provides that the nano zeolite layer is placed on the phosphor layer as an intermediate layer between the surface of the device (usually vitreous and transparent) and the phosphor layer, whereby it is no longer in direct contact with the inside of the device. In this case, the nano zeolite can also be mixed with alumina or other oxide particles to enhance the protection of the glass. There are two advantages in this case: on the one hand, a barrier to water is formed by degassing the glass, thereby protecting the phosphor. In addition to this effect, it has been surprisingly found in this case to use a particle size between 80 and 400 nm (hence, as explained above, 95% of the zeolite used is within this range) Rice zeolite provides advantages with respect to luminescence intensity. These nanostructures with sizes between 60 and 100 nanometers are more effective in this particular configuration. In particular, the particle distribution peak is located at about 80 nm (i.e., 95% nano zeolite is in the range of 70-90 nm), and the best results are obtained.

The use of preferred particle sizes for the three different configurations shows that advantages and unexpected effects are also obtained from any possible combination between the particle sizes of the foregoing examples and nano zeolites.

The foregoing three embodiments may be combined with each other in various ways: for example, the phosphor layer may be interposed between two layers of nano zeolite (the first layer acts as an interface between the phosphor and the device surface, and the second layer acts as a phosphor and Between the interfaces between the internal environments of the devices).

Preferred methods for making the nano zeolite layer are spray coating, dip coating or spray drying techniques, see, for example, "The Chemistry of Artificial Lighting Devices-lamps, Phosphors and Cathode Ray Tubes", RC Ropp. ed. Elsevier 1993. Phosphor deposition techniques described on page 363.

Considering the use of a dispersant, a curing or Lehring process (heating in an air stream) can be combined with these deposition methods and used to remove the dispersant in those embodiments of the invention, or in some cases, if the nano zeolite is dispersed In a matrix that is not completely crosslinked or contains a polymeric matrix precursor, the polymeric matrix is polymerized. In some embodiments, the curing process has the dual purpose of removing the dispersant and curing the polymer matrix containing the nano zeolite.

In a second aspect of the invention, the invention relates to an electroluminescent device comprising a composite layer for converting UV light or blue light into visible light, the composite layer comprising a layer of phosphor combined with nano-sized zeolite, characterized in that The size of the 95% nano zeolite is between 60 and 400 nm.

The most interesting devices for applying the subject matter of the present invention are displays for viewing information (especially plasma displays), fluorescent lamps, discharge lamps, and phosphor white LEDs.

Example 1

Preparation of commercially available three-wavelength phosphor varnish for fluorescent lamps BaMg ₂ Al ₁₆ O ₂₇ :Eu ²⁺ (Ce _0.67 Tb _0.33 )MgAl ₁₁ O ₉ (Y _0.9 Eu _0.11 ) ₂ O ₃ , 400 g of phosphor mixed Containing 2 wt/wt% resin (POLYOX WSR N-750, Dow Chemical Company), 0.5 g surfactant (TERGINOL NP-6, Dow Chemical Company), 10 g triethanolamine and 0.1 g organic defoamer (commercial product) , under the trade name SAG 275B). This coating was deposited on a flat glass substrate by spray coating and heated at 350 ° C for 5 minutes to obtain a 15 nm thick layer (Sample 1). The conversion performance of the phosphor layer was measured by a 254 nm UV excitation using a fluorescence spectrometer with an integrating sphere. The measured conversion performance is about 60%.

Two other samples were prepared by applying a coating to the phosphor layer. Sample 2 was obtained using a 800 nm thick conversion layer having a peak size of 300 nm nano zeolite. Instead, zeolites having an average size of 2 microns were deposited into a 4 micron thick layer to give Sample 3. For the two samples, the zeolite deposition method was a blade coating technique of an aqueous dispersion of a generally known zeolite (concentration of about 10% by weight/weight), followed by coagulation treatment at 100 ° C for 30 minutes.

The conversion efficiency measured by Sample 2 was improved by more than 10% compared to the efficiency observed from Sample 1, and the conversion efficiency measured by Sample 3 was reduced by more than 10% compared to the efficiency observed from Sample 1. The results are summarized in Table 1.

Claims (18)

A composite layer for converting UV light or blue light into visible light, comprising a layer of phosphor combined with nano-sized zeolite, characterized in that the size of the 95% nano zeolite is between 60 and 400 nm. The composite layer of claim 1, wherein the nano zeolite is dispersed in a transparent polymerizable matrix. The composite layer of claim 1, wherein the nano zeolite is uniformly dispersed together with the phosphor. The composite layer of claim 3, wherein 95% of the nano zeolite has a size between 80 and 150 nm. The composite layer of claim 4, wherein 95% of the nano zeolite has a size between 90 and 110 nm. The composite layer of claim 1, wherein the nano zeolite forms a coating overlying the phosphor layer. The composite layer of claim 6 wherein 95% of the nano zeolite has a size between 250 and 350 nm. For example, in the composite layer of claim 7, wherein 95% of the nano zeolite has a size between 280 and 320 nm. The composite layer of claim 1, wherein the nano zeolite forms an intermediate layer between the phosphor layer and the transparent substrate. A composite layer according to claim 9 wherein 95% of the nano zeolite has a size between 60 and 100 nm. The composite layer of claim 10, wherein 95% of the nano zeolite has a size between 70 and 90 nm. An electroluminescent device comprising a composite layer for converting UV light or blue light into visible light, the composite layer comprising a layer of phosphor combined with nano-sized zeolite, characterized in that the size of the 95% nano zeolite is between 60 and 400 Between the rice. The electroluminescent device of claim 12, wherein the nano zeolite forms a coating overlying the phosphor layer, the cladding being internal to the device. An electroluminescent device according to claim 12, wherein the nano zeolite forms an intermediate layer between the phosphor layer and the transparent substrate. An electroluminescent device according to claim 12, wherein the device is a plasma display. An electroluminescent device according to claim 12, wherein the device is a fluorescent lamp. An electroluminescent device according to claim 12, wherein the device is a discharge lamp. An electroluminescent device according to claim 12, wherein the device is a phosphor white LED.