CN102732247A - Method for preparing silicate fluorescent powder and silicate fluorescent powder prepared by same - Google Patents

Abstract

The invention relates to a method for preparing silicate phosphor powder and the silicate phosphor powder prepared therefrom. The silicate phosphor powder has the general formula (Ba _2-xy M _x )SiO ₄ :Eu _y , Among them, 0≤2-xy<2.0, 0≤x<2.0, 0<y<0.5, and M is Mg, Ca or Sr or any combination thereof, and has improved heat resistance, moisture resistance and luminous intensity. The method includes providing a precursor and sintering the precursor, the precursor including a seed crystal of the silicate phosphor.

Description

Method for preparing silicate phosphor and silicate phosphor prepared therefrom

technical field

The present invention relates to a preparation with general formula (Ba _2-xy M _x )SiO ₄ :Eu _y (0≤2-xy<2.0, 0≤x<2.0, 0<y<0.5, and M is Mg, Ca or Sr or their combination in any proportion) method for silicate phosphor and the silicate phosphor produced therefrom; especially relate to a phosphor that uses the same general formula as the desired silicate phosphor as crystal A method for preparing silicate phosphor and the silicate phosphor thus prepared.

Background technique

White light-emitting diodes are known as "green lighting sources" because they are both energy-saving and environmentally friendly. Based on the environmental awareness of saving carbon and sustainable development, advanced countries in the world are gradually replacing traditional lighting equipment with white light-emitting diodes. Early white light-emitting diodes were composed of a variety of light-emitting diodes with different wavelengths. However, this type of device has disadvantages such as large size, poor luminous efficiency, and uneven color mixing, making it difficult to apply to lighting devices that require high illuminance.

As far as the principle of light emission is concerned, most of today's white light-emitting diodes are composed of a single-wavelength light source (light-emitting diode chip) and at least one phosphor powder that can be excited by the light source. The light emitted by the light source (not absorbed by the phosphor) is mixed into white light. As far as the structure is concerned, in the white light emitting diode, the phosphor powder and the encapsulating material such as epoxy resin are firstly mixed to form an encapsulating colloid, and then a light source is coated with the colloid to form a white light emitting diode.

The current range of phosphors is rather limited. Japan's Nichia Chemical Company discloses a cerium-doped yttrium aluminum garnet (Cerium-doped yttrium aluminum garnet; YAG: Ce) phosphor in US Patent No. 5,998,925A, which can be affected by blue light-emitting diodes (such as nitride Gallium diode) excites and emits yellow light with a wavelength of about 550 nanometers, which is further mixed with unabsorbed blue light to form white light. However, white light emitting diodes using only YAG:Ce are inferior to traditional lighting devices in terms of color rendering and color temperature due to the lack of a complete full-spectrum band. In addition to YAG:Ce phosphors, Toyoda Gosei Corporation disclosed a series of silicate phosphors in US patents US 6,943,380B2 and US 6,809,347B2, which can produce blue-green, yellow-green and yellow fluorescence. Among them, the luminous efficiency of yellow-emitting silicate phosphors can match that of YAG:Ce, while green-emitting silicate phosphors can be matched with blue LEDs and red phosphors to provide white with full-spectrum bands. led. Therefore, the industry currently regards silicate phosphor as another mainstream besides YAG:Ce phosphor.

At present, the solid state reaction method is mostly adopted to produce silicate phosphor, such as the process disclosed in the aforementioned US Patent No. 6,809,347B2. In the solid-state reaction method, the required precursors are mainly weighed according to the ratio of elements in the general formula of the desired phosphor, and after grinding and mixing, the precursor is heat-treated in a reducing atmosphere to provide the desired phosphor. However, phosphors synthesized by this process generally have poor heat resistance and humidity resistance, and there is still room for improvement in luminous intensity.

In view of this, the present invention provides a novel method for preparing silicate phosphor, which is to improve the characteristics of silicate phosphor prepared by traditional solid-state reaction method through the application of seed crystals.

Contents of the invention

The main purpose of the present invention is to provide a method for preparing silicate phosphor, the silicate has the general formula (Ba _2-xy M _x )SiO ₄ :Eu _y , where 0≤2-xy<2.0, 0≤ x<2.0, 0<y<0.5, and M is Mg, Ca or Sr or any combination thereof, the method includes providing a precursor and sintering the precursor, wherein the precursor includes a silicate phosphor of seed crystals.

Another object of the present invention is to provide a silicate phosphor prepared by the aforementioned method. Compared with the silicate phosphor prepared by the traditional solid-state reaction method without using seed crystals, The silicate phosphor has enhanced heat resistance and moisture resistance, and the luminous intensity can be increased by about 2% to 10%.

In order to make the above-mentioned purpose, technical features and advantages of the present invention more comprehensible, some specific implementations are described below in detail.

Description of drawings

Fig. 1 shows the scanning electron microscope image of the silicate phosphor powder of comparative example;

Fig. 2 shows the scanning electron microscope image of the silicate phosphor of the embodiment;

Fig. 3 shows the excitation spectrum and emission spectrum of the silicate fluorescent powder of embodiment and comparative example;

Fig. 4 shows the thermal characteristic trend figure of the silicate phosphor of embodiment and comparative example; And

FIG. 5 is a trend graph showing the moisture resistance of the silicate phosphors of the embodiment and the comparative example.

Detailed ways

Some specific implementations according to the present invention will be described in detail below; without departing from the spirit of the present invention, the present invention can still be practiced in many different forms, and the protection scope of the present invention should not be interpreted as being limited to what is stated in the description specific implementation. Furthermore, as used in this specification (and especially in the claims), "a", "the", and similar terms should be understood to include both the singular and the plural unless the context dictates otherwise.

The traditional solid-state reaction method is to uniformly mix the components of the precursor, and then sinter the precursor to obtain the desired silicate phosphor. The inventors of the present invention have found that when the traditional solid-state reaction method is used to prepare silicate phosphor, if the seed crystal of the silicate phosphor is added to the precursor, the properties of the prepared silicate phosphor can be improved. properties, especially in terms of heat resistance, moisture resistance and luminous intensity. Therefore, the present invention provides a method for preparing silicate phosphor, the silicate has the general formula (Ba _2-xy M _x )SiO ₄ :Eu _y , wherein 0≤2-xy<2.0, 0≤x< 2.0, 0<y<0.5, and M is Mg, Ca or Sr or any combination thereof (for example, when M is a combination of Mg and Ca, the composition of M is Mg _n Ca _1-n (0<n<1 )), and the method includes providing a precursor and performing a sintering process on the precursor, wherein the precursor includes a seed crystal having the same general formula as the desired silicate phosphor.

For convenience of description, hereinafter, the traditional solid-state reaction method (that is, the precursor does not contain crystal seeds) for the preparation of silicate phosphors is referred to as "primary growth"; The method of the present invention in which the prepared phosphor is used as a seed crystal to prepare the silicate phosphor is called "secondary growth".

In the method of the present invention, the heat treatment process involved is the heat treatment of the existing known solid-state reaction method, and is used to thermally decompose, oxidize or gasify the components of the precursor, so as to achieve the growth of desired silicate fluorescence. The purpose of powder grains. Therefore, the above object can be achieved by a single sintering step in the method of the present invention. However, in order to effectively control the quality stability of the obtained phosphor, it is preferable to perform a calcinating step on the precursor before the sintering step to oxidize and escape other undesirable substances, and then proceed to the calcination step. The sintering step ensures that the crystal can grow stably without impurity interference to form the desired silicate phosphor.

In addition, as shown in the specific implementation method of this specification, after the aforementioned sintering treatment, the sintering can be carried out again under a reducing atmosphere, so as to reduce Eu ³⁺ in the crystal to Eu ²⁺ and improve the silicic acid produced. The glow effect of salt phosphor.

In the method of the present invention, the operating conditions (such as heat treatment temperature, temperature rise/fall rate) involved in sintering and calcination are the methods adopted in the existing known solid-state reaction method, depending on the composition of the precursor used, and its temperature should be Not lower than the thermal decomposition temperature of each component of the precursor. For example, when BaCO ₃ , SrCO ₃ , SiO ₂ , and Eu ₂ O ₃ are used to mix desired precursors to form silicate phosphor, it can be carried out at about 900° C. to about 1100° C. under air atmosphere. temperature for a calcination treatment; and then a sintering treatment at a temperature of about 1100°C to about 1500°C in _an air atmosphere; finally, if necessary, at a _temperature of about 1100°C to about 1100°C to A second sintering is carried out at a temperature of about 1500°C. Those skilled in the art can select appropriate operating conditions to implement the heat treatment process of the present invention according to their common knowledge and according to the composition of the precursors used after viewing the disclosure in this specification.

In addition, considering that the powder usually produces agglomerates after heat treatment, it is possible to grind the powder obtained from each heat treatment during the heat treatment process and between different treatment stages (such as between calcination treatment and sintering treatment) to uniformly disperse Each component, but the degree of grinding applied is based on the principle that the characteristics of the silicate phosphor are not affected. In addition, the precursor may also be ground before the heat treatment process to assist the components of the precursor to mix uniformly. The above-mentioned grinding means can be realized by, for example, a mortar.

Without being limited by theory, the inventor believes that in the method of the present invention, the seed crystal used is used as the growth nucleus, and the surface of the crystal seed crystal has been formed to epitaxially grow larger in size and have higher crystallinity. silicate phosphor, and can reduce the surface defects of silicate phosphor. As shown in the specific embodiment of this specification, compared with the silicate phosphor prepared under the same conditions but without using a seed crystal, the luminous intensity of the silicate phosphor prepared by the method of the present invention can be increased by about 2%. to about 10%.

The seed crystal used in the method of the present invention can be prepared by any convenient method, as long as its general formula is (Ba _2-xy M _x )SiO ₄ :Eu _y . For example, the phosphor powder prepared by the traditional solid state reaction method can be used as the seed crystal. In a specific embodiment of the present invention, the solid-state reaction method using the same reaction temperature, time and atmosphere is used to prepare the used seed crystal and the final silicate phosphor product, and only the latter (that is, the final silicate phosphor product The reaction precursor of the product) additionally includes the former (ie, the seed crystal). That is to say, the silicate phosphor powder with the desired element ratio is first prepared with the selected precursor and heat treatment process as the seed crystal (one-time growth), and then the obtained seed crystal is mixed into the same phosphor by the method of the present invention. Precursor combination, and the same heat treatment conditions to prepare the desired silicate phosphor (secondary growth).

In the method of the present invention, considering the crystal growth benefit, based on the weight of the precursor, it is preferred to contain about 1% by weight to about 50% by weight, preferably about 5% by weight to about 20% by weight, in the phosphor precursor. Seed. If the content of the seed crystal is less than 1% by weight, the effect of adding the seed crystal cannot be shown; and if the content of the seed crystal is greater than 50% by weight, the content of other components of the precursor will be too low at this time, resulting in "secondary growth" effect is not obvious. There is no special limitation on the size of the seed crystals. Considering that the silicate phosphor used in today's white light emitting devices is usually micron-sized, it is preferable to use a seed crystal smaller than 50 microns. In one embodiment of the invention, seeds having a particle size of about 10 microns to about 20 microns are used.

In the method of the present invention, as the prior known solid-state reaction method, the phosphor precursor used can include Ba, M (Mg, Ca or Sr or their arbitrary ratio combination), Si and Eu's respective salts (comprising hydrates of their salts). Taking M as Sr as an example, the precursor may include: Si oxides, nitrates or carbonates or their mixtures; Eu oxides, nitrates or carbonates or their mixtures; Ba oxides, nitrates or carbonates or mixtures thereof; and oxides, nitrates or carbonates or mixtures thereof of Sr. The ratio of Ba salt, M salt, Si salt and Eu salt in the precursor depends on the desired silicate phosphor (Ba _2-xy M _x ) SiO ₄ :Eu _y (the type of M and x, y and the value of 2-xy as defined above) depends on the stoichiometric proportion of Ba, M, Si and Eu. For example, when using a precursor mixed with BaCO ₃ , SrCO ₃ , SiO ₂ and Eu ₂ O ₃ to prepare a silicate phosphor with the general formula (Ba _0.5 Sr _1.38 )SiO ₄ :Eu _0.12 , at this time Ba: The molar ratio of Sr:Si:Eu is 0.5:1.38:1:0.12, so the molar ratio of BaCO ₃ :SrCO ₃ :SiO ₂ :Eu ₂ O ₃ must be 0.5:1.38:1:0.06. Based on the teaching of this specification, those skilled in the art can use different raw materials and proportions according to their common knowledge, and use the method of the present invention to prepare the silicate phosphor with the desired general formula, which has improved properties.

Therefore, the present invention further provides a silicate phosphor, which is prepared by the method of the present invention. Compared with the phosphor prepared from the precursor without seed crystals, the phosphor of the present invention has improved heat resistance , moisture resistance and luminous intensity, it has great industrial application value.

The present invention is further illustrated by the following specific embodiments with reference to the corresponding drawings.

A. Preparation of silicate phosphor

[Comparative example: Silicate phosphor powder I grown at one time]

BaCO ₃ , SrCO ₃ , SiO ₂ , and Eu ₂ O ₃ were weighed in a molar ratio of 0.5:1.38:1:0.06, and the resulting mixture was ground to serve as a precursor. The precursor is placed in a high-temperature furnace, heated to about 1000°C at a rate of 5°C/min in an air atmosphere, and calcined at about 1000°C for about 6 hours, and then cooled to room temperature at a rate of 5°C/min. The resulting product was ground into a homogeneous powder with a mortar. Next, put the powder in a high-temperature furnace, heat up to about 1250°C at a rate of 5°C/min in an air atmosphere, and sinter at about 1250°C for about 6 hours, and then cool at a rate of 5°C/min After reaching room temperature, the obtained product was ground into a homogeneous powder with a mortar. Finally, put the powder in a high-temperature furnace, raise the temperature to about 1250°C at a rate of 5°C/min under H ₂ /N ₂ (5%/95%) atmosphere, and sinter at about 1250°C for about 6 hours, then cooled to room temperature at a rate of 5°C/min, and ground the obtained product into a uniform powder with a mortar to obtain a primary growth silicate phosphor I(Ba _0.5 Sr _1.38 )SiO ₄ :Eu _0.12 .

[Example: Silicate Phosphor Powder II of Secondary Growth]

The preparation process of the comparative example was repeated to prepare the secondary growth silicate phosphor II (Ba _0.5 Sr _1.38 )SiO ₄ :Eu _0.12 . The only difference in the preparation is that 10% by weight (based on the weight of the precursor) of silicate phosphor I prepared in the comparative example is added to the precursor as a seed crystal.

B. Analysis of silicate phosphor

Silicate phosphor I (comparative example) and silicate phosphor II (embodiment) are analyzed as follows respectively:

Using Hitachi S-2400 electron microscope to scan silicate phosphor I and silicate phosphor II, the images are shown in Figure 1 and Figure 2 respectively. It can be seen from Figure 1 that the average particle size of the silicate phosphor I grown once is about 10 microns to 20 microns, and it can be seen from Figure 2 that the average particle size of the silicate phosphor II grown secondary The particle size grows to 15 microns to 30 microns.

FluoroMax-3 spectrometer was used to test the excitation and emission spectra of silicate phosphor I and silicate phosphor II respectively, and the results are shown in FIG. 3 . Can be divided into left and right two curves in Fig. 3. The left curve (wavelength from 300 nm to about 530 nm) is the excitation spectrum of the silicate phosphor; the right curve (about 480 nm to 700 nm) is the emission spectrum of the silicate phosphor. From the emission spectrum in Figure 3 (right curve), the strongest emission wavelength of silicate phosphor (Ba _0.5 Sr _1.38 ) SiO ₄ :Eu _0.12 is about 540 nm. In terms of emission intensity at this wavelength, silicic acid The radiation intensity of the salt phosphor powder II is at least about 3% higher than that of the silicate phosphor powder I, which proves that the method of the present invention can indeed increase the luminous intensity of the prepared silicate phosphor powder.

FluoroMax-3 spectrometer was used to test the relationship between the radiation intensity of the silicate phosphor I and the silicate phosphor II and the temperature change, and the results are shown in FIG. 4 . It can be seen from FIG. 4 that when the temperature increases from 25° C. to 300° C., the luminous intensity of the silicate phosphor that has undergone primary growth or secondary growth will decrease as the temperature rises. However, it can be found in FIG. 4 that at high temperature (especially after 150° C.), the decline rate of the silicate phosphor II after the secondary growth is smaller than that of the silicate phosphor I after the primary growth. This shows that the silicate phosphor prepared by the method of the present invention has better heat resistance, which is beneficial to reduce the risk of failure of the light-emitting device at high temperature.

Use HANNA HI2300 to test the degree of dissociation of the distilled aqueous solution dispersed with silicate phosphor I and silicate phosphor II, and record the change of dissociation degree with time (measurement time 1 hour). The results are shown in Figure 5 shown. It can be seen from FIG. 5 that the dissociation rate of the silicate phosphor II (corresponding to the slope of conductivity versus time) is lower than that of the silicate phosphor I, which means it has better moisture resistance. This is because the secondary grown silicate phosphor II has better crystallinity, which is beneficial to the stability of the phosphor in long-term use.

The above-mentioned embodiments are only illustrative to illustrate the principles and effects of the present invention, and explain the technical features of the present invention, but are not intended to limit the scope of protection of the present invention. Any change or arrangement that can be easily accomplished by those skilled in the art without violating the technical principle and spirit of the present invention falls within the protection scope of the present invention.

Claims (10)

1. A method for preparing silicate phosphor, characterized in that, the silicate phosphor has the general formula (Ba _2-xy M _x ) SiO ₄ :Eu _y , wherein 0≤2-xy<2.0, 0 ≤x<2.0, 0<y<0.5, and M is Mg, Ca or Sr or any combination thereof, the method includes providing a precursor and sintering the precursor, wherein the precursor comprises the silicate phosphor Seed. 2. The method according to claim 1, further comprising calcining the precursor before the sintering step. 3. The method according to claim 2, wherein the calcining step is performed at a temperature of 900°C to 1100°C; and the sintering step is performed at a temperature of 1100°C to 1500°C. 4. The method according to any one of claims 1 to 3, wherein the precursor comprises: (1) oxides, nitrates or carbonates of Si or mixtures thereof; (2) Eu (3) Ba oxides, nitrates or carbonates or their mixtures; and (4) Sr oxides, nitrates or carbonates or their mixture. 5. The method according to claim 4, wherein the precursor comprises BaCO ₃ , SrCO ₃ , SiO ₂ and Eu ₂ O ₃ . 6. The method according to any one of claims 1-3, wherein based on the weight of the precursor, the content of the seed crystal is 1 wt% to 50 wt%. 7 . The method according to claim 6 , wherein based on the weight of the precursor, the content of the seed crystal is 5 wt % to 20 wt %. 8. The method according to any one of claims 1 to 3, wherein the particle size of the seed crystals is less than 50 microns. 9. A silicate phosphor produced by the method according to any one of claims 1 to 8. 10 . The silicate phosphor according to claim 9 , wherein the silicate phosphor is (Ba _0.5 Sr _1.38 )SiO ₄ :Eu _0.12 .

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