WO2023104217A1 - Eu2+ doped tantalate red phosphor and preparation method therefor - Google Patents

Abstract

The invention belongs to the technical field of inorganic luminescent materials, and specifically relates to an Eu2+ doped tantalate red phosphor and a preparation method therefor. In the red ceramic phosphor capable of being excited by blue light, the oxide Sr3TaO5.5 serves as a phosphor matrix, and is doped with Eu2+ to achieve high-performance red light emission. The red ceramic phosphor applicable to high-power white-light LED illumination of the present invention shows a high luminous intensity and a very good thermal stability. When combined with a green-light or yellow-light ceramic phosphor in the prior art, the red ceramic phosphor is expected to achieve efficient white light under the excitation of blue light, and has an absolute improvement effect on optimizing the color rendering performance of a white-light LED.

Description

A kind of Eu2+ doped tantalate red phosphor and preparation method thereof technical field

The invention belongs to the technical field of inorganic luminescent materials, and specifically relates to a Eu ²⁺ doped tantalate red powder phosphor and a red ceramic phosphor that can be excited by blue light, and more specifically relates to a Eu ²⁺ doped red ceramic Phosphor powder preparation method.

Background technique

At present, due to the continuous optimization of light-emitting diodes (LEDs), especially InGaN chips in the 450-460nm band are already the most efficient chips. The development of phosphors that can be excited by blue light is an effective way to realize high-performance devices. In particular, the development of rare earth-doped luminescent materials has become a hot topic in the research field. White LED (WLED) has received more and more attention in recent years because of its huge application potential in the field of solid-state lighting, and is known as the fourth-generation green lighting source. At present, the light-converting white LEDs that can be industrialized are usually obtained by using blue-light InGaN chips to excite YAG:Ce ³⁺ yellow phosphor powder. This kind of white light LED has a simple manufacturing principle and high luminous efficiency, and has been applied in many fields. However, the obtained devices have a low color rendering index due to the lack of red light emission spectrum, which usually makes WLEDs have a low color rendering index (<80) and a high correlated color temperature (>4500K), which limits its application. Especially in some fields such as artistic lighting and medical lighting that have high requirements on color temperature and color rendering. Therefore, in order to meet the requirements of high-quality lighting, WLEDs must have high color rendering index (>80), high lumen efficiency (>90lm/W) and low correlated color temperature (2700-4500K).

The way to make white LEDs is mainly composed of blue LED chips and red/green phosphors or blue LED chips and yellow phosphors; based on considerations of device cost, ease of implementation, and light color quality, people often use these two methods. way to achieve white LED light emission. At present, the existing red phosphor systems for white LEDs include sulfide system red phosphors, silicon nitride (oxide) oxide system red phosphors, and silicates, borates, phosphates and scandates, etc. Red phosphor. However, the stability and anti-ultraviolet radiation ability of sulfide are poor, and the service life of white light LED is not long. At the same time, this type of phosphor is sensitive to humidity and has poor stability; Requires harsh conditions such as high temperature and high pressure, which increases the cost and safety hazards; the red phosphor of silicate, borate, phosphate and scandate system has good chemical stability and thermal stability, but the color rendering index of the packaged product is generally not tall. In addition, the current commercial red phosphors such as Mn ⁴⁺ doped fluoride red phosphors have the advantages of narrow emission spectrum and high color purity, but a large amount of corrosive HF is used in the synthesis process, and Poor stability in high humidity environment.

In summary, current solutions for fabricating high-quality pc-WLEDs ( R _a >80, CCT <4500 K) in solid-state lighting rely on red-emitting phosphors. Therefore, the present invention is committed to providing a novel red ceramic phosphor that can be excited by blue light, has high efficiency and good thermal stability, thereby complementing the missing red light band in white LEDs, increasing the service life of white LEDs, and improving Color rendering properties of white LEDs.

Conventional WLEDs, such as the combination of blue LEDs with yellow YAG:Ce phosphors, have R _a < 75 due to the insufficient spectrum in the red region. As we all know, the junction temperature of high-power WLEDs can reach 150-200°C under working conditions, which imposes strict requirements on the thermal characteristics of the encapsulants used. Generally, silicone resins or resins with low thermal conductivity (0.1-0.2 W/mK) and poor thermal stability will inevitably have serious yellowing and aging problems in high-temperature environments, resulting in decreased luminous efficiency and discoloration. Therefore, many researchers in industry and academia have devoted themselves to the development of all-inorganic phosphors.

Most high-efficiency red phosphors are rare earth ion-activated materials that have been used since the 1960s, and have been developed from the aspects of composition, performance, and preparation technology. As demand increases, solid-state lighting using LEDs begins to show a trend of accelerated development. People have accelerated the research on new substrates, developed new red phosphors, and improved the existing synthesis methods of red phosphors to meet the needs of large-scale applications. Eu ²⁺ doped alkaline earth metal sulfides CaS and SrS can generate red light excited by blue light (430~500 nm) (C. Guo, D. Huang, Q. Su, Mater. Sci. Engineering: B 2006, 130, 189.). Therefore, it can be excited by blue LED chips and act as the red component of white LEDs, with low color temperature and high color rendering. Nitride (Ca,Sr)AlSiN ₃ :Eu ²⁺ , (Y. Tsai, C. Chiang, W. Zhou, JF Lee, H. Sheu and R. Liu, J. Am. Chem. Soc., 2015, 137 , 8936-8939.), Sr[LiAl ₃ N ₄ ]:Eu ²⁺ , (P. Pust, AS Wochnik, E. Baumann, PJ Schmidt, D. Wiechert, C. Scheu and W. Schnick, Chem. Mater. , 2014, 26, 3544-3549.) and M ₂ Si ₅ N ₈ :Eu ²⁺ (M=Ca, Sr, Ba) (CW Yeh, WT Chen, RS Liu, SF Hu, HS Sheu, JM Chen and HT Hintzen, J. Am. Chem. Soc., 2012, 134, 14108-14117.) Phosphor powders have excellent photoluminescent properties, including broad excitation bands, high quantum efficiency, and good thermal stability. In addition, the quantum efficiency of M ₂ Si ₅ N ₈ :Eu ²⁺ can be improved by substituting Ca for Ba and Sr under blue light irradiation. The absorption efficiency, internal quantum efficiency and external quantum efficiency of Sr ₂ Si ₅ N ₈ :Eu ²⁺ (2mol%) are 82%, 87% and 71%, respectively. At 150 °C, the quantum efficiency hardly drops, indicating weaker thermal quenching. However, alkaline earth metal sulfide red phosphors have many deficiencies in terms of physical and chemical properties. The preparation conditions of nitride-based red phosphors are harsh. The luminescent material with garnet crystal structure is usually called garnet phosphor, and its composition can be represented by the general formula [A] ₃ [B] ₂ (C) ₃ O ₁₂ . These hosts exhibit excellent luminescent and lasing properties when doped with rare earth or transition metal ions. The garnet-structured Lu ₂ CaMg ₂ (SiGe) ₃ O ₁₂ :Ce ³⁺ exhibits a broadband red emission with a full width at half maximum of 150 nm and a center at 605 nm under excitation at 470 nm. (H. Lin, B. Wang, Q. Huang, F. Huang, J. Xu, H. Chen, Z. Lin, J. Wang, T. Hu and Y. Wang, J. Mater. Chem. C, 2016 , 4, 10329-10338.) A white LED obtained by combining with a 470 nm chip exhibits a color temperature of 3500 K. These red phosphors play a vital role in improving the performance of white LEDs. At present, Eu ²⁺ doped high-efficiency red phosphors have been widely disclosed, such as Sr ₂ Sc _0.5 Ga _1.5 O ₅ :Eu ²⁺ , literature (Z. Yang, Y. Zhou, J. Qiao, MS Molokeev, Z. Xia , Adv. Opt. Mater. 2021, 9, 2100131.), Sr ₂ LaTaO ₆ :Eu ³⁺ , (Q Tang, T Yang, H Huang, J Ao, B Guo. Optik Inter. J. Light and Electron Opt. , 2021, 240:166908.), due to the perovskite structure, there will be many similar characteristics, but there are great differences. Each matrix has unique properties. When doped Eu ²⁺ enters the matrix, the positions of the replaced atoms are different, and the luminescence performance will be different. For example, the peak position of luminescence is different, and the thermal stability of luminescence is different. It also has a great influence on the valence state of the activator Eu. For example, the luminescence of Eu ³⁺ in Sr ₂ LaTaO ₆ is completely different. It mainly emits some sharp lines and cannot be excited by blue light, so the luminous efficiency will be relatively low, which will limit its practical application in white LEDs.

Some documents also reported the structure of Sr ₃ TaO _5.5 (LH Brixner, J. Am. Chem. Soc. 1958, 80, 3214.), which is consistent with the structure of the present invention. The researchers of this document conducted a detailed study on the matrix structure , which laid the foundation for the development of luminescent materials. The present invention is researched on the basis of such documents. The difference of the present invention mainly lies in the activator Eu ²⁺ , and a small amount of addition will produce peculiar luminous characteristics. The present invention focuses on Eu ²⁺ to study the luminous performance, because Eu ²⁺ will produce strong red light emission phenomenon in Sr ₃ TaO _5.5 , thus satisfying the red light band missing in current white light lighting. The powder phosphor has some limitations in actual use, so the powder phosphor can be further transformed into a bulk phosphor, which can be used more widely. Most of the currently reported red-light ceramic phosphors are composite materials, for example, mixing phosphor powder with glass powder or ceramic powder, and then calcining to obtain red-light emitting glass or ceramics. The blocks obtained in this way The luminous efficiency of bulk materials is usually not too high, mainly because of the influence of impurities. It is because the impurities will absorb the light emitted by the phosphor, resulting in low luminous efficiency of this type of ceramic or glass. Therefore, the direct implementation of powder phosphor powder into ceramic phosphor powder is the fundamental reason for improving the luminous efficiency of bulk materials. Therefore, the present invention directly implements ceramic phosphors, thereby obtaining red light ceramics with high luminous efficiency (see FIG. 5a ) and good thermal stability (see FIG. 5b ).

technical solution

For this reason, the technical problem to be solved by the present invention is to provide a Sr ₃ TaO _5.5 :Eu ²⁺ red phosphor that can be excited by blue light, so as to solve the problem of unsatisfactory luminous efficiency and stability of the red phosphor in the prior art .

The second technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned Sr ₃ TaO _5.5 :Eu ²⁺ red ceramic phosphor that can be excited by blue light. It is expected to be used in LED devices, so as to complement the missing red light band in white LEDs, so as to increase the service life of WLEDs and improve the color rendering performance of WLEDs.

Technical scheme of the present invention is as follows:

In order to solve the above technical problems, the present invention provides a red phosphor that can be excited by blue light. The chemical composition of the red ceramic phosphor is Sr ₃ TaO _5.5 : x Eu ²⁺ , where 0.01≤x≤0.20 ; And take Eu ²⁺ as the luminescent center.

A preparation method of Eu ²⁺ doped tantalate red phosphor, using a high-temperature solid-phase method, annealing the raw material at 1400°C to obtain the red phosphor; the raw material includes strontium source, tantalum source and flux.

A method for preparing Eu ²⁺ doped tantalate red ceramic phosphors, using a high-temperature solid-phase method, annealing the raw materials at 1400°C, and then annealing at 1600°C to obtain red ceramic phosphors; Said raw materials include strontium source, tantalum source and flux.

In the above method, the strontium source used is at least one kind of strontium carbonate and a compound that can be converted into strontium oxide.

In the above method, the tantalum source used is at least one kind of tantalum pentoxide and a compound capable of being converted into tantalum pentoxide.

In the above method, the flux is diboron trioxide, or at least one compound that can be converted into diboron trioxide.

A preparation method of Eu ²⁺ doped tantalate red phosphor, comprising the following steps:

(1) Accurately weigh the raw materials according to the stoichiometric ratio of the general formula Sr ₃ TaO _5.5 :xEu ²⁺ , where 0.01≤x≤0.20, and weigh 0.5%-10% of the total mass of flux, and fully grind and mix , to obtain the raw material mixture;

(2) Calcining the raw material mixture obtained in step (1) in a reducing atmosphere.

In the above method, the specific calcining step includes: keeping the temperature at 1200-1400° C. for 4 hours, and then cooling down naturally, so as to obtain the powdery phosphor.

In the above method, the specific calcination steps include: keeping the temperature at 1200-1400° C. for 4 hours, raising the temperature again to 1500-1700° C. and keeping it for 8 hours, and then cooling down naturally to obtain the ceramic phosphor.

In the above method, the reducing atmosphere is a mixed gas with a concentration of 10-20% H ₂ to 80-90% N ₂ by volume as the reducing atmosphere.

Beneficial effect

The advantages of the present invention are:

The red ceramic phosphor that can be excited by blue light according to the present invention uses the oxide Sr ₃ TaO _5.5 as the ceramic phosphor matrix, and is doped with Eu ²⁺ to realize red light emission. It not only has a stable structure but also has excellent thermal stability. The color rendering properties of LEDs offer potential options.

The red ceramic phosphor powder of the present invention that can be used for high-power white LED lighting applications has high luminous intensity and excellent thermal stability. Combining it with green or yellow ceramic phosphors in the prior art is expected to achieve high-efficiency white light under blue light excitation, which will definitely improve the color rendering performance of white LEDs.

Description of drawings

Figure 1a is the phase diagram of Sr ₃ TaO _5.5 : x Eu ²⁺ , ( x =0.02) red powdery phosphor described in Example 1;

Figure 1b is the excitation and emission spectra of the Sr ₃ TaO _5.5 : x Eu ²⁺ , ( x =0.02) red powdery phosphor described in Example 1;

Figure 2 a shows the Sr ₃ TaO _5.5 : x Eu ²⁺ , ( x =0.06) red powder phosphor described in Example 2 and the Sr ₃ TaO _5.5 : x Eu ²⁺ described in Example 3, ( x =0.06) Phase diagram of ceramic-like phosphor;

Figure 2b shows the Sr ₃ TaO _5.5 : x Eu ²⁺ , ( x =0.06) red powder phosphor described in Example 2 and the Sr ₃ TaO _5.5 : x Eu ²⁺ , ( x =0.06) ceramics described in Example 3 Excitation and emission spectra of the phosphor powder;

Fig. 3 a is the phase diagram of Sr ₃ TaO _5.5 : x Eu ²⁺ , ( x = 0.08) red powdery phosphor described in Example 4;

Fig. 3b is the excitation and emission spectra of the red Sr ₃ TaO _5.5 : x Eu ²⁺ , ( x = 0.08) toner phosphor described in Example 4;

Fig. 4a is a quantum efficiency diagram of Sr ₃ TaO _5.5 : x Eu ²⁺ , ( x =0.06) ceramic-like phosphor described in Example 3.

Fig. 4b is the variable temperature spectrum of Example 3 Sr ₃ TaO _5.5 : x Eu ²⁺ , ( x =0.06).

Embodiments of the present invention

In order to make the content of the present invention more easily understood, the present invention will be described in further detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings

Example 1

Weigh 3.0 mmol of raw materials SrCO ₃ , 0.5 mmol of Ta ₂ O ₅ , 0.02 mmol of Eu ₂ O ₃ , and weigh 3% of B ₂ O ₃ with a total mass of 3%. In %H ₂ -80%N ₂ atmosphere, heat up to 1400°C for sintering for 6 hours, then cool down to room temperature, take it out, grind it into powder, and obtain the powdery red powder phosphor of this embodiment.

The red powdery fluorescent powder described in this embodiment exhibits light orange-yellow body color under natural light, and bright red color under 450nm excitation. The fluorescent powder of the present invention corresponds completely to the standard card, and the phase diagram is shown in Figure 1a. Show. Its excitation and emission spectra are shown in accompanying drawing 1b, monitor sample with 620nm wavelength, can obtain the excitation peak of a 250-600nm broadband, measure the excitation spectrum of sample with optimal excitation wavelength 450nm, obviously, in the scope of 540-800nm Inside there is a broadband transmitter.

Example 2

Weigh 3.0 mmol of raw materials SrCO ₃ , 0.5 mmol of Ta ₂ O ₅ , 0.06 mmol of Eu ₂ O ₃ , and weigh 3% of B ₂ O ₃ with a total mass of 3%. In %H ₂ -80%N ₂ atmosphere, heat up to 1400°C for sintering for 6 hours, then cool down to room temperature, take it out, grind it into powder, and obtain the powdery red powder phosphor of this embodiment.

The red powdery fluorescent powder described in this embodiment has a light orange-yellow body color under natural light, and a bright red color under 450nm excitation. The red powdery fluorescent powder described in this embodiment completely corresponds to the standard card, and the phase diagram As shown in Figure 2a. Its excitation and emission spectra are shown in accompanying drawing 2b, monitor sample with 620nm wavelength, can obtain the excitation peak of a 250-600nm broadband, measure the excitation spectrum of sample with optimal excitation wavelength 450nm, obviously, in the range of 540-800nm Inside there is a broadband transmitter.

Example 3

Weigh 3.0 mmol of raw materials SrCO ₃ , 0.5 mmol of Ta ₂ O ₅ , 0.06 mmol of Eu ₂ O ₃ , and weigh 3% of B ₂ O ₃ with a total mass of 3%. In %H ₂ -80% N ₂ atmosphere, heat up to 1400°C for sintering for 6 hours, continue to heat up to 1600°C for 6 hours, then cool down to 1100°C after 6 hours, naturally cool down to room temperature, and take it out to obtain the red ceramic fluorescent light of this example. pink.

The red ceramic fluorescent powder in this embodiment, under the irradiation of natural light and 450nm blue light, the ceramics appear orange-yellow and bright red. The red ceramic fluorescent powder described in this embodiment completely corresponds to the standard card; the phase diagram is shown in Figure 2a. Its excitation and emission spectra are shown in accompanying drawing 2b, monitor sample with 620nm wavelength, can obtain the excitation peak of a 250-600nm broadband, measure the excitation spectrum of sample with optimal excitation wavelength 450nm, obviously, in the range of 540-800nm Inside there is a broadband transmitter.

Example 4

Weigh 3.0 mmol of raw materials SrCO ₃ , 0.5 mmol of Ta ₂ O ₅ , 0.08 mmol of Eu ₂ O ₃ , and weigh 3% of B ₂ O ₃ with a total mass of 3%. In %H ₂ -80%N ₂ atmosphere, heat up to 1400°C for sintering for 6 hours, then cool down to room temperature, take it out, grind it into powder, and obtain the powdery red powder phosphor of this embodiment.

The red powdery fluorescent powder described in this embodiment has a light orange-yellow body color under natural light, and a bright red color under 450nm excitation. The red powdery fluorescent powder described in this embodiment completely corresponds to the standard card, and the phase diagram As shown in Figure 3a. Its excitation and emission spectra are shown in accompanying drawing 3b, monitor sample with 620nm wavelength, can obtain the excitation peak of a 250-600nm broadband, measure the excitation spectrum of sample with optimal excitation wavelength 450nm, obviously, in the scope of 540-800nm Inside there is a broadband transmitter.

Example 5

Weigh 3.0 mmol of raw materials SrCO ₃ , 0.5 mmol of Ta ₂ O ₅ , 0.10 mmol of Eu ₂ O ₃ , and weigh 3% of B ₂ O ₃ with a total mass of 3%. In %H ₂ -80%N ₂ atmosphere, heat up to 1400°C for sintering for 6 hours, then cool down to room temperature, take it out, grind it into powder, and obtain the powdery red powder phosphor of this embodiment.

The red powdery fluorescent powder described in this embodiment has a light orange-yellow body color under natural light, and a bright red color under 450nm excitation. The red powdery fluorescent powder described in this embodiment completely corresponds to the standard card, and the phase diagram As shown in Figure 4a. Its excitation and emission spectra are shown in accompanying drawing 4b, monitor sample with 620nm wavelength, can obtain the excitation peak of a 250-600nm broadband, measure the excitation spectrum of sample with optimum excitation wavelength 450nm, obviously, in the scope of 540-800nm Inside there is a broadband transmitter.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Within the spirit and principle of the present invention, any modification, ion equivalent replacement, improvement, etc., are included in the protection scope of the present invention.

Claims (10)

1. A Eu ²⁺ doped tantalate red phosphor, characterized in that its chemical composition formula is Sr ₃ TaO _5.5 : x Eu ²⁺ , 0.01≤x≤0.20 , and Eu ²⁺ is the luminescent center.
2. The method for preparing the Eu ²⁺ doped tantalate red phosphor according to claim 1 is characterized in that the red phosphor can be obtained by annealing the raw material at 1400° C. by using a high-temperature solid-phase method; the raw material Includes strontium source, tantalum source and flux.
3. The method for preparing the Eu ²⁺ doped tantalate red phosphor according to claim 1 is characterized in that the raw material is annealed at 1400°C by using a high-temperature solid-state method, and then annealed at 1600°C to obtain Red ceramic fluorescent powder; the raw materials include strontium source, tantalum source and flux.
4. The method according to claim 2 or 3, characterized in that the strontium source used is at least one of strontium carbonate and a compound that can be converted into strontium oxide.
5. The method according to claim 2 or 3, characterized in that the tantalum source used is at least one of tantalum pentoxide and a compound capable of being converted into tantalum pentoxide.
6. The method according to claim 2 or 3, characterized in that the flux is diboron trioxide, or at least one compound that can be converted into diboron trioxide.
7. According to the method described in any one of claims 2～6, it is characterized in that comprising the following steps:

   (1) Accurately weigh the raw materials according to the stoichiometric ratio of the general formula Sr ₃ TaO _5.5 : x Eu ²⁺ , where 0.01≤ x ≤0.20, and weigh 0.5%-10% of the total mass of flux, and fully grind and mix homogeneously to obtain a mixture of raw materials;

   (2) Calcining the raw material mixture obtained in step (1) in a reducing atmosphere.
8. The method according to claim 7, wherein the specific calcining step comprises: keeping the temperature at 1200-1400° C. for 4 hours, and then cooling down naturally, so as to obtain powdery phosphor.
9. The method according to claim 7, characterized in that the specific calcining step comprises: keeping the temperature at 1200-1400°C for 4 hours, then raising the temperature to 1500-1700°C for 8 hours, and then cooling down naturally to obtain the ceramic phosphor.
10. The method according to claim 7, characterized in that the reducing atmosphere is a mixed gas with a volume percent concentration of 10-20% H ₂ -80-90% N ₂ as the reducing atmosphere.

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