CN102092951A - Transparent glass ceramic material for ultraviolet excited white LED and preparation technique thereof - Google Patents

Abstract

The invention discloses a transparent glass ceramic material used for ultraviolet light to excite white light LEDs and a preparation technology thereof. The composition of the glass ceramics is SiO ₂ : 40-60mol%; Al ₂ O ₃ : 10-30mol%; CeF ₃ : 5-25mol%; NaF: 0-15mol%; LiF: 0-15mol%; ReF ₃ : 0.01-5mol%; MSO ₄ : <0.5%; Fe: <0.02%. Among them, Re represents rare earth ions (such as Eu, Tb, Dy, etc.), M represents Mg or Ca or Ba or Sr; the content of NaF and LiF is not zero at the same time. The preparation process of the glass ceramics includes two steps of preparation of precursor glass by melt quenching method and subsequent crystallization treatment of precursor glass. By changing the rare earth doping, the glass-ceramic of the present invention can produce intense multicolor (including white light) tunable luminescence under the excitation of ultraviolet light, which is expected to be developed and applied to the construction of new white light LED devices excited by ultraviolet chips.

Description

Transparent glass-ceramic material and its preparation technology for white light LED excited by ultraviolet light

technical field

The invention relates to the field of solid luminescent materials, in particular to a rare earth-doped transparent glass ceramic capable of realizing multicolor (including white light) tunable luminescence under ultraviolet light excitation conditions and its preparation technology.

technical background

In recent years, white light-emitting diode (LED) lighting, which has unique advantages such as energy saving and durability, has attracted great attention from people. At present, it has gradually become a trend to replace traditional incandescent and fluorescent lamps with white LEDs. Currently common commercial white LEDs are made by encapsulating blue GaN chips and Ce ³⁺ -doped yttrium aluminum garnet (YAG) phosphors, which are mixed in epoxy resin and coated on the chips. Part of the blue light emitted by the GaN LED chip is absorbed by the phosphor, causing it to be excited to emit yellow light, and the unabsorbed blue light is mixed with the yellow light emitted by the phosphor to obtain white light. Because the luminous life of the blue light chip and the YAG phosphor is different, after a period of use, the luminous color of the LED will produce color difference. In order to solve this problem, white light LEDs can be manufactured by coating special phosphor powder with ultraviolet light chips. At this time, the ultraviolet light emitted by the chip that cannot be seen by the naked eye is completely absorbed by the phosphor, so that the phosphor is stimulated to emit blue light and yellow light (or red, green, and blue three-color light), and white light is obtained after mixing. Using this technology can basically avoid chromatic aberration, but due to the aging of epoxy resin under long-term ultraviolet light irradiation, the service life of white light LED devices will be shortened. Research and development of new solid luminescent materials that emit intense white light under the excitation of ultraviolet light and are resistant to ultraviolet light irradiation (stable structure and performance) is the latest direction in the development of white light LED technology in the world [Y. Zheng, AG Clare, Phys. Chem. Glasses ., 46, 467 (2005)].

Rare earth-doped transparent oxyfluoride glass-ceramic is obtained by partial crystallization of inorganic glassy materials, and its structural feature is that specific fluoride nanocrystals are evenly embedded in the glass matrix. As a new type of solid luminescent material, it combines the advantages of fluoride crystals and glass materials. It can have optical properties similar to or even better than crystals, and has the advantages of simple preparation technology, thermal stability and chemical stability similar to glass materials. high advantage. The transparent glass-ceramic that emits intense white light under the excitation of ultraviolet light can be processed into a flat plate and directly covered on the chip. Therefore, it is expected to be used to replace conventional phosphors to build new white LED devices. Compared with conventional LED devices, this new device will have the remarkable advantages of stable light color and long service life.

The invention relates to a kind of transparent glass ceramics containing cerium fluoride (CeF ₃ ) nanocrystals doped with rare earth ions and its preparation technology. In the present invention, rare earth ions are doped into CeF ₃ nano crystal glass ceramics as luminescent centers, and the rare earth ions enter CeF ₃ nano crystals by controlling the crystallization conditions of CeF ₃ . The reason for choosing CeF ₃ as the matrix of the rare earth luminescent center is that Ce ³⁺ ions have a 4f-5d transition allowed by the electric dipole in the ultraviolet region, so they have a very strong absorption cross section for ultraviolet light. In addition, Ce ³⁺ ions are easy to transfer the absorbed UV light energy to other rare earth ions to produce efficient visible light emission. The test results show that after the Ce ³⁺ ions in the glass ceramics of the present invention are excited by ultraviolet light, they transfer energy to the rare earth ions enriched in the CeF ₃ nanocrystals, thereby producing efficient multicolor (including white light) tunable luminescence.

Contents of the invention

The present invention proposes a rare earth-doped CeF ₃ nanocrystal-containing transparent glass ceramic component and its preparation process, with the purpose of preparing a solid luminescent material that is expected to be applied to a new type of white light LED device and has multi-color tunable luminous characteristics.

Component and mole percentage of transparent glass-ceramic of the present invention are as follows:

SiO ₂ : 40-60mol%; Al ₂ O ₃ : 10-30mol%; CeF ₃ : 5-25mol%; NaF: 0-15mol%; LiF: 0-15mol%; ReF ₃ : 0.01-5mol%; MSO ₄ Fe: <0.5%; Fe: <0.02%. Among them, Re represents rare earth ions (such as Eu, Tb, Dy, etc.), M represents Mg or Ca or Ba or Sr; the content of NaF and LiF is not zero at the same time. The glass ceramic has the following microstructural features: CeF ₃ nanocrystals with a hexagonal structure are uniformly distributed in a glass matrix, the grain size is 10-15 nanometers, and doped rare earth ions are segregated in the CeF ₃ nanocrystals.

The glass ceramics of the present invention are prepared by melt quenching and subsequent heat treatment.

The melt quenching method and subsequent heat treatment adopted in the present invention include two steps of precursor glass preparation and precursor glass crystallization treatment. During the crystallization process of the precursor glass, the heat treatment temperature is 600°C-720°C.

By changing the rare earth doping, the glass ceramics of the present invention can produce intense multicolor (including white light) tunable luminescence under the excitation of ultraviolet light.

The glass-ceramic of the present invention has simple preparation process, low cost, non-toxicity and pollution-free, good thermal and chemical stability, and is expected to be developed and applied to construct novel white light LED devices excited by ultraviolet chips.

Description of drawings

Fig. 1 is the X-ray diffraction spectrum of example 1 glass ceramics;

Fig. 2 is the high-resolution transmission electron microscope bright-field image of example 1 glass ceramics;

Fig. 3 is the excitation spectrogram corresponding to 407 nanometers of emission of example 1 glass ceramics;

Fig. 4 is the fluorescence spectrogram of example 1 glass-ceramic under the excitation of 335 nanometer wavelength;

Fig. 5 is the excitation spectrogram corresponding to 591 nanometers emission of example 2 glass ceramics;

Fig. 6 is the fluorescence spectrogram of example 2 glass ceramics under the excitation of 394 nanometer wavelength;

Fig. 7 is the excitation spectrogram corresponding to 543 nanometers emission of example 3 glass ceramics;

Fig. 8 is the fluorescence spectrogram of example 3 glass ceramics under the excitation of 335 nanometer wavelength;

Fig. 9 is the excitation spectrogram corresponding to 578 nanometers emission of example 4 glass ceramics;

Fig. 10 is a fluorescence spectrum diagram of the glass-ceramic of Example 4 excited at a wavelength of 335 nm.

Detailed ways

Weigh various powder raw materials according to a certain composition ratio, mix and grind them in an agate mortar, put them in a crucible, put them in a resistance furnace, heat them to 1300-1700°C, keep them warm for 1-12 hours to melt them, and then , Take out the molten glass and quickly pour it into a copper mold to form a bulk precursor glass; put the obtained precursor glass into a resistance furnace for annealing to eliminate internal stress. The glass is subjected to differential thermal analysis, and its glass transition temperature and first crystallization temperature are measured. A temperature is selected between the glass transition temperature and the first crystallization temperature, and isothermal heat treatment is carried out on the above glass for 1 to 10 hours to partially crystallize it to obtain transparent glass ceramics.

The crucible used in the preparation process can be a platinum crucible or a corundum crucible.

By adopting the above material components and preparation process, a transparent glass ceramic in which CeF ₃ nanocrystals are evenly embedded in an oxide glass matrix can be obtained. Electron spectroscopy and spectral analysis results show that the doped rare earth ions enter the nanocrystalline phase. According to different rare earth doping conditions, the glass-ceramic materials respectively produce intense polychromatic light emission under the excitation of ultraviolet light.

Example 1: The analytically pure SiO ₂ , Al ₂ O ₃ , NaF and CeF ₃ powders were accurately weighed according to the ratio of 50SiO ₂ : 25Al ₂ O ₃ : 15NaF : 10CeF ₃ (molar ratio) and placed in the agate laboratory. In the bowl, grind for more than half an hour to make it evenly mixed, then put it into a platinum crucible, heat it to 1400°C in a program-controlled high-temperature box-type resistance furnace, and keep it warm for 3 hours, then quickly pour the molten glass into a copper mold to form; The obtained precursor glass was put into a resistance furnace, annealed at 530°C for 2 hours, and then cooled with the furnace to eliminate internal stress. According to the results of differential thermal analysis, the annealed glass was kept at 650°C for 2 hours to obtain taupe transparent glass ceramics. X-ray diffraction results (as shown in Figure 1) show that the CeF _crystal phase of hexagonal structure is separated out in the glass matrix; transmission electron microscope observation (as shown in Figure 2) shows that a large number of sizes in this glass ceramics are 10-15 nanometers CeF ₃ grains are evenly distributed in the glass matrix.

The samples were polished, and their excitation and emission spectra at room temperature were measured with a FLS920 fluorescence spectrometer. On monitoring the excitation spectrum of the 407 nm emission of Ce ³⁺ ions, an excitation band corresponding to the ultraviolet band (225-385 nm) of Ce ³⁺ : 4f→5d transition was detected (as shown in FIG. 3 ). On the emission spectrum excited at 335 nm, there appears a strong blue light emission corresponding to the Ce ³⁺ : 5d→4f transition (center wavelength is 407 nm) (as shown in FIG. 4 ).

Example 2: Analytical pure SiO ₂ , Al ₂ O ₃ , LiF, CeF ₃ and EuF ₃ powders with a purity of 99.99%, according to 0.1EuF ₃ : 50SiO ₂ : 25Al ₂ O _{3 :} 9.9LiF : 15CeF ₃ (mol ratio) and placed in an agate mortar after being accurately weighed, ground for more than half an hour to make it evenly mixed, then placed in a platinum crucible, heated to 1350°C in a program-controlled high-temperature box-type resistance furnace, and kept for 6 hours, then , quickly pour the glass melt into a copper mold to form it; put the obtained precursor glass into a resistance furnace, anneal at 500°C for 2 hours and then cool with the furnace to eliminate internal stress; according to the results of differential thermal analysis, the annealed glass It was kept at 600° C. for 2 hours to obtain taupe transparent glass ceramics. The results of X-ray diffraction showed that CeF ₃ crystal phase with hexagonal structure was precipitated in the glass matrix; transmission electron microscope observation showed that a large number of CeF ₃ grains with a size of 10-15 nanometers in the glass ceramics were uniformly distributed in the glass matrix; And spectral analysis showed that rare earth ions Eu ³⁺ segregated in CeF ₃ nanocrystals.

The samples were polished, and their excitation and emission spectra at room temperature were measured with a FLS920 fluorescence spectrometer. On monitoring the excitation spectrum of Eu ³⁺ ions emitted at 591 nanometers, an excitation band (as shown in Figure 5) corresponding to the ultraviolet-visible band (350-480 nanometers) of Eu ³⁺ : 4f → 4f transition is detected; at 394 On the nano-excited emission spectrum, an emission peak corresponding to the Eu ³⁺ : 4f→4f transition appears (as shown in FIG. 6 ), and the glass-ceramic sample emits bright red light when observed with naked eyes.

Example 3: Analytical pure SiO ₂ , Al ₂ O ₃ , NaF, CeF ₃ and TbF ₃ powders with a purity of 99.99%, according to 0.5TbF ₃ : 55SiO ₂ : 25Al ₂ O _{3 :} 12.5NaF : 7CeF ₃ (mol ratio) and put it in an agate mortar, grind it for more than half an hour to make it evenly mixed, then put it into a platinum crucible, heat it to 1500°C in a program-controlled high-temperature box-type resistance furnace, and keep it warm for 6 hours, then , quickly pour the glass melt into a copper mold to form it; put the obtained precursor glass into a resistance furnace, anneal at 550°C for 2 hours and then cool with the furnace to eliminate internal stress; according to the results of differential thermal analysis, the annealed glass It was kept at 670° C. for 2 hours to obtain taupe transparent glass ceramics. X-ray diffraction results show that the hexagonal CeF ₃ crystal phase is precipitated in the glass matrix; transmission electron microscope observation shows that a large number of CeF ₃ grains with a size of 10-15 nanometers in the glass ceramics are uniformly distributed in the glass matrix; And spectroscopic analysis showed that rare earth ions Tb ³⁺ segregated in CeF ₃ nanocrystals.

The samples were polished, and their excitation and emission spectra at room temperature were measured with a FLS920 fluorescence spectrometer. In monitoring the excitation spectrum of Tb ³⁺ ion emission at 543 nanometers, the excitation bands corresponding to the UV-visible band (225-500 nanometers) of Ce ³⁺ : 4f→5d transition and Tb ³⁺ : 4f→4f transition were detected ( As shown in Figure 7), it shows that there is effective energy transfer of Ce ³⁺ ions to Tb ³⁺ ions in glass ceramics; on the emission spectrum excited at 335 nm, there is an emission peak corresponding to Tb ³⁺ : 4f→4f transition (As shown in Figure 8), the glass-ceramic sample emits bright green light when observed with the naked eye.

The energy transfer efficiency from Ce ³⁺ ions to Tb ³⁺ ions can be improved by optimizing the concentration of rare earth doping, thereby enhancing the green emission of glass ceramics. The experimental results show that as the doping concentration of Tb ³⁺ increases from 0.1 mol% to 2.0 mol%, the luminescence intensity and lifetime of Ce ³⁺ ions at 407 nm decrease monotonously, while the green luminescence intensity of Tb ³⁺ ions monotonically increased, indicating that the energy transfer efficiency from Ce ³⁺ to Tb ³⁺ increased gradually. The highest energy transfer efficiency of the system can reach 80%.

Example 4: The analytically pure SiO ₂ , Al ₂ O ₃ , NaF, CeF ₃ and DyF ₃ powders with a purity of 99.99% were mixed according to 1.0 DyF ₃ : 44SiO ₂ : 28Al ₂ O _{3 :} 16NaF : 11CeF ₃ (molar ratio ) was accurately weighed and placed in an agate mortar, ground for more than half an hour to make it evenly mixed, then placed in a platinum crucible, heated to 1400°C in a program-controlled high-temperature box-type resistance furnace, and kept for 1 hour, then, The molten glass was quickly poured into a copper mold to form it; the obtained precursor glass was placed in a resistance furnace, annealed at 550°C for 2 hours and then cooled with the furnace to eliminate internal stress; according to the results of differential thermal analysis, the annealed glass was 650 ° C for 4 hours to obtain taupe transparent glass ceramics. The results of X-ray diffraction showed that CeF ₃ crystal phase with hexagonal structure was precipitated in the glass matrix; transmission electron microscope observation showed that a large number of CeF ₃ grains with a size of 10-15 nanometers in the glass ceramics were uniformly distributed in the glass matrix; And spectroscopic analysis showed that rare earth ions Dy ³⁺ segregated in CeF ₃ nanocrystals.

The samples were polished, and their excitation and emission spectra at room temperature were measured with a FLS920 fluorescence spectrometer. In monitoring the excitation spectrum of Dy ³⁺ ion emission at 578 nm, the excitation bands corresponding to Ce ³⁺ : 4f→5d transition and Dy ³⁺ : 4f→4f transition in the ultraviolet-visible band (225-500 nm) were detected ( As shown in Figure 9), it shows that there is effective energy transfer of Ce ³⁺ ions to Dy ³⁺ ions in glass ceramics; on the emission spectrum excited at 335 nm, there is an emission peak corresponding to Dy ³⁺ : 4f→4f transition (As shown in Figure 10), the glass-ceramic sample emits bright white light when observed with naked eyes. The luminous color of the glass-ceramic sample is represented by the 1931-CIE chromaticity coordinate diagram, and the calculation results show that the chromaticity coordinate values are CIE-X=0.348, CIE-Y=0.366, which are very close to the standard equal-energy white light emission coordinates.

The energy transfer efficiency from Ce ³⁺ ions to Dy ³⁺ ions can be improved by optimizing the doping concentration of rare earths, thereby enhancing the white light emission of glass ceramics. The experimental results show that as the Dy ³⁺ doping concentration increases from 0.1 mol% to 2.0 mol%, the luminescence intensity and lifetime of Ce ³⁺ ions at 407 nm decrease monotonously, while the white light luminescence intensity of Dy ³⁺ ions monotonically increases , indicating that the energy transfer efficiency from Ce ³⁺ to Dy ³⁺ increases gradually. The highest energy transfer efficiency of the system can reach 85%.

Claims (3)

1. a class can realize comprising the tunable luminous rare earth doping transparent glass-ceramic of polychrome of white light under the ultraviolet excitation condition, and its component is SiO ₂: 40-60mol%, Al ₂O ₃: 10-30mol%, CeF ₃: 5-25mol%, NaF:0-15mol%, LiF:0-15mol%, ReF ₃: 0.01-5mol%, MSO ₄:＜0.5%, Fe:＜0.02%; Wherein, Re represents rare earth ion Eu, Tb or Dy, and M represents Mg, Ca, Ba, Sr; NaF and LiF content are not 0 simultaneously; This glass-ceramic has following micro-structural feature: the CeF of uniform distribution hexagonal structure in glass basis ₃Nanocrystalline, crystal particle scale is the 10-15 nanometer, and the Doped Rare Earth ion aggregation is in CeF ₃In nanocrystalline.

2. the preparation method of transparent glass ceramics as claimed in claim 1 comprises the steps:

(1) forerunner's glass melt quench preparation;

(2) crystallization and thermal treatment of forerunner's glass.

3. the preparation method of transparent glass ceramics as claimed in claim 2, it is characterized in that: in the crystallization process of described forerunner's glass, thermal treatment temp is 600 ℃-720 ℃.

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