Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
  • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
  • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
  • C09K11/7766—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals
  • C09K11/7774—Aluminates
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B33/00—Electroluminescent light sources
  • H05B33/12—Light sources with substantially two-dimensional radiating surfaces
  • H05B33/14—Light sources with substantially two-dimensional radiating surfaces characterised by the chemical or physical composition or the arrangement of the electroluminescent material, or by the simultaneous addition of the electroluminescent material in or onto the light source

Definitions

• Embodiments of the present disclosure are directed in to yellow-green to yellow- emitting phosphors based on aluminates that contain the rare earth terbium (Tb).
• Tb rare earth terbium
• Such phosphors are applicable to a number of different technologic areas, including general lighting systems, white light illumination systems based on white LEDs, signal lights; indicator lights, etc., as well as display applications such as display backlighting, plasma display panels, LED- based display panels, and the like.
• Embodiments of the present invention are directed to aluminate-based phosphors that, when activated by cerium, and when doped with the rare earth terbium (Tb) emit visible light in the yellow-green to yellow portion of the electromagnetic spectrum.
• the phosphor may also include the rare earths lutetium (Lu) and/or gadolinium (Gd).
• the phrase "visible light in the yellow-green to yellow portion of the electromagnetic spectrum" is defined to mean light having a peak emission wavelength of about 550 nm to about 600 nm.
• Such phosphors may be used in commercial markets where white light is generated using so-called "white light LEDs,” noting as an aside that this term is somewhat of a misnomer, since light emitting diodes emit light of a specific monochromatic color and not a combination of wavelengths perceived as white by the human eye. The term is nonetheless entrenched in the lexicon of the lighting industry.
• YAG:Ce yittrium aluminate garnet activated with cerium
• YAG:Ce has a relatively high absorption efficiency when excited by blue light, is stable in high temperature and humidity environments, and has a high quantum efficiency (QE>95%), all the while displaying a broad emission spectrum.
• YAG:Ce cerium doped Lu 3 AI 5 0i2 compound
• LAG:Ce cerium doped Lu 3 AI 5 0i2 compound
• LAG:Ce exhibits a different peak emission wavelength than its YAG counterpart; in the lutetium case, this peak wavelength is at about 540 nm. This emission wavelength is still not short enough, however, to be ideal for certain applications such as backlighting applications, and general lighting applications, where appropriate.
• a phosphor with a structure comparable to a garnet in terms of temperature and humidity stability, but having at the same time a peak emission wavelength ranging from about 550 nm to about 600 nm.
• these challenges may be addressed by providing lutetium (Lu) aluminate-based phosphors that include the rare earth terbium (Tb).
• the phosphors may also include the rare earth gadolinium (Gd).
• Embodiments of the present disclosure are directed to yellow-green and yellow- emitting, lutetium aluminate-based phosphors containing terbium (Tb) and in some embodiments gadol inium (Gd) in addition to Tb. These phosphors may be used in white LEDs, in genera! lighting applications, and in LED and backlighting displays.
• Tb terbium
• Gd gadol inium
• the phosphor may comprise a cerium- activated, yellow-green to yellow-emitting lutetium aluminate-based phosphor comprising terbium (Tb), aluminum (A ), and oxygen (O), wherein the phosphor is configured to absorb excitation radiation having a wavelength ranging from about 380 nm to about 480 nm, and to emit light having a peak emission wavelength ranging from about 550 nm to about 600 nm.
• the yellow-green to yellow-emitting aluminate-based phosphor may be excited by radiation having a wavelength ranging from about 420 nm to about 480 nm.
• the phosphor may have the formula (Lui -x Tb x )3AlsOi2:Ce, wherein x ranges from about 0.1 to less than 1.0, and wherein the phosphor is configured to absorb excitation radiation having a wavelength ranging from about 380 nm to about 480 nm, and to emit light having a peak emission wavelength ranging from about 550 nm to about 565 nm.
• the phosphor may further include the rare earth element gadolinium (Gd) and have the formula (Lui -x- y b x Gd y ) AI 5 0 i 2:Ce, whereinx ranges from about 0.
• the Tb-containing phosphors may have a shift in CIE coordinates of less than 0.005 for both x and y coordinates over a temperature range from 20 °C to 220 °C - specific examples of such phosphors include (Lu 0 .6iTbo.3Ce 0 .o )3Al50i2, (Luo ⁇ iTbo.sCeo.o ⁇ AlsOu and (Luo.4iGdo.2Tbo.3Ceo,o )3Al50 t2.
• the phosphor comprises a cerium- activated, yellow-green to yellow-emitting aluminate-based phosphor having the formula (Lu ! -X- y A x Cey)3B z AI 5 0 i2C2 Z ; wherein A is Tb; B is at least one of Mg, Sr, Ca, and Ba; C is at least one of F, CI, Br, and I; 0.001 ⁇ x ⁇ 1.0; 0.001 ⁇ y ⁇ 0.2; and 0 ⁇ z ⁇ 0.5. .
• the phosphor comprises a cerium- activated, yellow-green to yellow-emitting aluminate-based phosphor represented by the formula (Luo.9i-xA x Ceo.o )3Al 5 Oi2-
• A is Tb, and may further include Gd; and x ranges from about 0.00 1 to about 1.0.
• a white light illumination system may comprise: an excitation source with emission wavelength within a range of 200nm to 480nm; at least one of a red-emitting phosphor or a green-emitting phosphor; and a cerium- activated, yellow-green to yellow-emitting lutetium aluminate-based phosphor comprising terbium, wherein the phosphor is configured to emit light having a peak emission wavelength ranging from about 550 nm to about 565 nm.
• the cerium-activated, yellow-green to yellow- emitting lutetium aluminate-based phosphor may be configured to absorb excitation radiation having a wavelength ranging from about 380 nm to about 480 nm.
• the cerium-activated, yellow-green to yellow-emitting lutetium aluminate-based phosphor may further comprise gadolinium.
• FIG. 1 shows the SEM morphology of Lu 2 , iCeo.o A lsOi2 with different MgF 2 additive concentrations, illustrating that particle sizes become larger and more homogeneous as the amount of the gF 2 additive is increased;
• FIG. 2 is a series of x-ray diffraction (XRD) patterns of exemplary Y2.9iCeo.o9Al 5 Oi 2 phosphors with different MgF 2 additive concentrations;
• FIG.3 is a series x-ray diffraction (XRD) patterns of exemplary Lu 2 ⁇ Ceo ⁇ AlsO ⁇ phosphors with different MgF 2 additive concentrations;
• FIG. 4 is a series of the x-ray diffraction (XRD) patterns of exemplary Lu2. i Ce 0 .o Al 5 Oi 2 phosphors having a 5 wt% MgF 2 additive and a 5 wt% SrF 2 additive;
• FIG. 5 is the emission spectra of a series of exemplary Y 2 9i Ce 0 .09Al5O] 2 phosphors with different levels of MgF 2 additive, the emission spectra are obtained by exciting the phosphors with a blue LED;
• FIG. 6 is the normalized emission spectra of a series of exemplary Lu 2 .9i Ceo.o9Al 5 O i 2 phosphors with different MgF 2 additive concentrations under blue LED excitation;
• FIG. 7 is the emission spectra of Lu 2 .9iCeo.o9Al 5 Oi 2 phosphors with different MgF 2 additive concentrations under blue LED excitation;
• FIG. 8 is the normalized emission spectra of Lu2. i Ceo,o Al 5 0
• FTG. 9 is a normalized emission spectra of a phosphor with 5wt% gF 2 and 5wt%SrF 2 additives where the phosphor has been excited with a blue LED; the results are compared with a control sample that contains no halogenated salt additives; the results illustrate that the emission peak shifts to shorter wavelengths with the MgF 2 synthesized compound than it does for the SrF 2 synthesized compound;
• FIG. 10 shows how the emission wavelength of a series of exemplary Lu2. i Ce 0, o9AI 5 Oi 2 p osphors decreases as the concentration of an SrF2 additive is increased;
• FIG. 1 1 is the normalized excitation spectra of a series of exemplar Lu 2, 9iCeo . o5AlsOi2 phosphors with different MgF 2 additive concentrations, showing that the excitation spectrum becomes narrower as the MgF 2 additive concentration is increased;
• FIG. 12 shows the temperature dependence of an exemplary Lu2. iCeo.o 9 AlsO
• FIG. 15 is the spectra of the white LED systems of FIG 14, in this instance measured at 3,000 K;
• FIGS. 16A-B shows that the peak emission wavelength of these halogenated aluminates ranged overall from about 550 nm to about 580 nm as the Gd level was increased, where the Ba level was fixed stoichiometrically at 0. 15 for the Ba series, and where the Sr level was fixed stoichiometrically at 0.34;
• FIGS. 1 7A-B are the x-ray diffraction patterns of both the Ba series and the Sr series of phosphors whose luminosity data was depicted in FIGS. I 6A-B;
• FIGS. 18-20 are photoemission spectra of representative Tb and/or Gd-containing phosphors excited by a blue light source, according to the present embodiments; the spectra plot photoluminescent intensity as a function of photoemission wavelength;
• FIG. 2 1 is is a plot of peak emission wavelength versus either Gd or Tb concentrations, and thus shows the effect of the amount of Gd and/or Tb inclusion on peak photoemission wavelength;
• FIG. 22 is a plot of photoluminescent intensity versus peak emission wavelength for the same series of phosphors with varying Gd concentration and Tb concentration studied in FIG. 21 ;
• FIG. 23 is a graph of the CIE y-coordinate plotted against CIE x-coordinate for a series of exemplary phosphors being subjected to an increase in temperature; the data shows that increasing temperature leads to a decrease in the value of the CIE y-coordinate CIE y-coordinate, and an increase in the CIE x-coordinate.
• a yttrium aluminum garnet compound activated with the rare earth cerium (YAG:Ce) has been, historically, one of the most common choices of phosphor material made if the desired application was either high power LED lighting, or cool white lighting of a non-specific, general nature. As one might expect, there is a requirement in general lighting for highly efficient components, both in the case of the LED chip supplying the blue light component of the resultant white light, and the excitation radiation for the phosphor, where the phosphor typically supplies the yellow/green constituent of the resulting product white light.
• YAG:Ce demonstrates this desired high efficiency, having a quantum efficiency greater than about 95 percent, and it would therefore appear to be a difficult task to improve upon this number.
• the efficiency of an LED chip increases with a decrease in emission wavelength, and thus it would appear, in theory anyway, that the efficiency of a general lighting system will be enhanced if a phosphor paired with an LED chip emitting at shorter wavelengths may be excited by those shorter wavelengths.
• the problem with this strategy is that the emission efficiency of a YAG:Ce phosphor decreases when the wavelength of its blue excitation radiation is reduced to a level below about 460 nm.
• one of the objects of the present invention include altering the structure and nature of this anionic polyhedron to shift the excitation range the phosphor "desires" to see to shorter wavelengths relative to that of the traditional YAG:Ce, while maintaining in the meantime (or even improving) the enhanced properties that many garnets display.
• the present disclosure will be divided into the following sections: first, a chemical description (using stoichiometric formulas) of the present halogenated aluminates will be given, followed by a brief description of viable synthetic methods that may be used to produce them. The structure of the present halogenated aluminates will be discussed next, along with its relationship to experimental data comprising wavelength and photoluminescent changes upon the inclusion of certain halogen dopants. Finally, the role these yellow-green and yellow-emitting phosphors may play in white light illumination, general lighting, and backlighting applications will be presented with exemplary data,
• the yellow to green-emitting, aluminate-based phosphors of the present invention contain both alkaline earth and halogen constituents. These dopants are used to achieve the desired photoemission intensity and spectral properties, but the fact that simultaneous alkaline earth and halogen substitutions provide a sort of self-contained charge balance is fortuitous as well. Additionally, there may be other advantageous compensations having to do with the overall changes to the size of the unit cell: while substitutions of any of Sc, La, Gd, and/orTb for Lu (either individually, or in combinations) may tend to expand or contract the size of the cell, the opposite effect may occur with substitutions of halogen for oxygen.
• a green emitting, cerium-doped, aluminate-based phosphor may be described by the formula (Lui. a-b-c Y fl b A c )3(AI
• the "A” element which may be any of the alkaline earth elements Mg, Sr, Ca, and Ba, used either solely or in combination, is very effective in shifting emission wavelength to shorter values. These compounds will be referred to in the present disclosure as “halogenated LAG- based” aluminates, or simply “halogenated aluminates.”
• the present yellow to green-emitting, aluminate-based phosphors may be described by the formula (Y,A) 3 (Al,B)5(0,C)i 2:Ce 3+ , where A is at least one of Tb, Gd, Sm, La, Lu, Sr, Ca, and Mg, including combinations of those elements, wherein the amount of substitution of those elements for Y ranges from about 0.1 to about 100 percent in a stoichiometric manner.
• B is at least one of Si, Ge, B, P, and Ga, including combinations, and these elements substitute for A I in amounts ranging from about 0.1 to about 100 percent stoichiometrical ly.
• C is at least one of F, CI, N, and S, including combinations, substituting for oxygen in amounts ranging from about 0. 1 to about 100 percent stoichiometrically.
• the present yellow to green-emitting, aluminate-based phosphors may be described by the formula (Y i-x B x)3Al5(Oi -y Cy)i2:Ce 3+ , where x and y each range from about 0.001 to about 0.2.
• a yellow-green to green-emitting, aluminate-based phosphor may be described by the formula (A where A is selected from the group consisting of Y, Sc, Gd, Tb, and Lu;B is selected from the group consisting of Mg, Sr, Ca, and Ba; C is selected from the group consisting of F, CI, and Br;0 ⁇ x ⁇ 0.5 ;0 ⁇ y ⁇ 0.5 ;2 ⁇ m ⁇ 4; and l 0 ⁇ n ⁇ 14.
• a yellow-green to green-emitting, aluminate-based phosphor may be described by the formula (Ai. x B x j m ls(Oi- y * C y ' ) n :Ce , where A is selected from the group consisting of Y, Sc, Gd, Tb, and Lu;B is selected from the group consisting of Mg, Sr, Ca, and Ba; C is selected from the group consisting of F, CI , and Br; 0 ⁇ x ⁇ 0.5;0 ⁇ y ⁇ 0.5;2
• a yellow-green to green-emitting, aluminate-based phosphor may be described by the formula (A i.x 3+ B x 2+ ) m Als(Oi .y Z" Cy' ' ) n :Ce 3+ , where A is selected from the group consisting of Y, Sc, Gd, Tb, and Lu;B is selected from the group consisting of Mg, Sr, Ca, and Ba; C is selected from the group consisting of F, CI, and Br;0 ⁇ x ⁇ 0.5;0 ⁇ y ⁇ 0.5 ;2
• a yellow to green-emitting, aluminate-based phosphor may be described by the formula (Lu i -x-y A x Ce y )3B z A l50i 2C2z, where A is at least one of Sc, La, Gd, and Tb; B is at least one of the alkaline earths Mg, Sr, Ca, and Ba; C is at least one of the halogen elements F, C, Br, and I; and the values of the parameters x, y, z are 0 ⁇ x ⁇ 0.5; 0.001 ⁇ y ⁇ 0.2; and 0.001 ⁇ z ⁇ 0.5.
• the amount of C is less than 2z in the formula of paragraph [0045] by an amount of up to 5 percent by number. In various other embodiments, the amount of C is less than 2z by an amount of up to 10, 25, and 50 percent stoichiometrically.
• Any number of methods may be used to synthesize the present yellow-green to yellow-emitting, aluminate-based phosphors, methods that may involve both solid state reaction mechanisms as well as liquid mixing techniques.
• Liquid mixing includes such methods as co- precipitation and sol-gel techniques.
• One embodiment of preparation involves a solid state reaction mechanism comprising the steps:
• step (b) the mix of starting powders from step (a) is dry-mixed using any conventional method, such as ball milling, and typical mixing times using ball milling are greater than about 2 hours (in one embodiment about 8 hours);
• step (c) sintering the mixed starting powders from step (b) at a temperature of about 1400°C to about 1600°C for about 6 to about 12 hours in a reducing atmosphere (the purpose of this atmosphere is for a reduction of the ammonia-based compounds);
• the present aluminates may be synthesized by liquid mixing techniques.
• An example of the synthesis of a non-halogenated LAG compound having the formula Lu 2 . 85Ceo.oi5Al50i2iising co-precipitation has been described by H.-L. Li et al. in an article titled "Fabrication of Transparent Cerium-Doped Lutetium Aluminum Garnet Ceramics by Co- Precipitation Routes," J. Am. Ceram. Soc.S9 [7] 2356-2358 (2006).
• non-halogenated LAG compounds contained no alkaline earth constituents.
• the article is incorporated herein in its entirety, as it is contemplated that a similar co-precipitation method may be used to produce the hatogenated LAGs of the present disclosure with alkaline earth constituents.
• FIG. 1 shows the SEM morphology of an exemplary Lu 2 . i Ceo.o9 l50 i2 phosphors with different MgF 2 additive concentrations, synthesized via the solid state mechanisms described above.
• the morphology as revealed by scanning electron microscope (SEM) shows that particle sizes become larger, and more homogeneous, as the amount of the MgF2 additive is increased.
• the phosphor particles are roughly 10 to 1 microns in diameter.
• the crystal structure of the present yellow-green to yellow aluminates is similar to that of the yttrium aluminum garnet, Y3AI5O 12, and in keeping with this well studied YAG compound, the present aluminates may belong to the space group Ia3d (no. 230).
• This space group as it pertains to YAG, has been discussed by Y. uru et al. in an article titled "Yttrium Aluminum Garnet as a Scavenger for Ca and Si," J. Am. Ceram. Soc.91 [1 1] 3663-3667 (2008). As described by Y.
• YAG has a complex crystal consisting of 160 atoms (8 formula units) per unit cell, where the Y 3+ occupy positions of multiplicity 24, Wyckoff letter "c,” and site symmetry 2.22, and the O 2" atoms occupy positions of multiplicity 96, Wyckoff letter "h,” and site symmetry 1.
• Two of the Al ions are situated on octahedral 16(a) positions, whereas the remaining three Al 3+ ions are positioned on tetrahedral 24(d) sites,
• FIG. 2 shows the x-ray diffraction (XRD) patterns of a series of exemplary Y2.9iCeo.o9AI 5 Ot2 phosphors with different MgF 2 additive concentrations, showing how the addition of an alkaline earth and a halogen (MgF 2 ) component shifts high angle diffraction peaks to higher values of 2 ⁇ .
• MgF 2 halogen
• FIG.3 shows the x-ray diffraction (XRD) pattern of a series of exemplary phosphors in an analogous manner to FIG. 2, except that this time the series of compounds are Lu2.9i Ceo o9Alf O i 2 phosphors with different MgF 2 additive concentrations, where lutetium-based compounds are being studied, rather than yttrium-based compounds.
• XRD x-ray diffraction
• FIG. 4 shows the x-ray diffraction (XRD) pattern of a series of exemplary Lu 2 9iCeo o9Al 5 Oi 2 phosphors having either a 5 wt% MgF 2 and 5 wt% SrF 2 additive: this experiment shows a comparison of the Mg constituent versus an Sr constituent.
• the data shows that with the MgF 2 additive in the Lu2.9i Ce 0 .o9Al 5 Oi2 lattice, high angle diffraction peak move to greater values of 2 ⁇ , meaning that lattice constants become smal ler.
• Ce 3+ is the luminescent activator in the aluminate-based phosphor.
• the transition between the 4f and 5d energy levels of the Ce 3+ ion corresponds to excitation of the phosphor with blue light; green light emission from the phosphor is a result from the same electronic transition.
• the Ce 3+ is located at the center of an octahedral site formed by a polyanionic structure of six oxygen ions. It will be appreciated by those skilled in the art that according to crystal field theory, the surrounding anions (which may also be described as ligands) induce an electrostatic potential on the 5d electron of the central cation.
• the 5d energy level splitting is l ODq, where Dq is known to depend on the particular ligand species. From the spectrochemical series it may be seen that the Dq of a halide is smaller than that of oxygen, and thus it follows that when oxygen ions are replaced by halide ions, the Dq will decrease correspondingly.
• the emitted luminescence will have a shorter wavelength than otherwise would have occurred.
• the cation replacing Lu is a larger cation, such as Sr or Ba
• the result will be a shift of the emission peak towards the red end of the spectrum.
• the emitted luminescence will have a longer wavelength.
• Mg as an alkaline earth substituent will be a better choice than Sr if a blue-shift is desired, and this will be shown experimentally in the following portions of the present disclosure.
• the LAG emission peak is a doublet due to spin-orbit coupling. As the blue-shift occurs, the emission with shorter wavelength is biased and its intensity increases correspondingly. This trend is not only helpful to the blue-shift of the emission, but also enhances photoluminescence.
• FIG. 5 is the emission spectra of a series of exemplary Y2. i Ceo.o Al50i2 phosphors with different levels of MgF 2 additive, the emission spectra obtained by exciting the phosphors with a blue LED.
• This data shows that with increasing amounts of MgF2 the photoluminescent intensity increases and the peak emission wavelength shifts to shorter values.
• the present inventors have data for a 5 wt% addition of BaF 2 to the starting powders: this phosphor showed a significant increase in photoluminescent intensity relative to the three magnesium-containing phosphors, and a peak emission wavelength that the same about as that of the I wt% sample.
• FIG. 6 is the normalized emission spectra of the same series of exemplary L ⁇ .si Ceo.ogAlsOn phosphors with different MgF 2 additive concentrations under blue LED excitation, but where normalizing the photoluminescent intensity to a single value highlight that the emission peak of Y2 iCe 0 o9Al 5 Oi 2Shifts to short wavelength with increasing amounts of the MgF 2 additive.
• FIG. 7 is the emission spectra of a series of exemplary Lu 2 . i Ceo.o9Al50i2 phosphors with different levels of MgF 2 additive, the emission spectra obtained by exciting the phosphor with a blue LED.
• This data is analogous to that of FIG. 5, except that lutetium-based rather than yttrium-based compounds are being studied. As with the yttrium data, this data for lutetium shows similar trends for the shift in emission wavelength, though those trends for photoluminescent intensity are not, perhaps, as similar.
• 2 emission spectra of FIG. 7 has been normalized to emphasize the effect of the addition of halogen salt on peak emission wavelength; the normalized version of the data is shown in FIG. 8.
• peak emission shifts to shorter wavelength with increasing amounts of MgF 2 additive; that is to say, the greater the amount of the MgF 2 additive, the shorter emission peak wavelength.
• the amount of wavelength shift upon increasing the amount of the MgF2 additive from zero (no additive) to about 5 wt% of the additive was observed to be about 40 nm; from about 550 nm to about 5 10 nm.
• FIGS. 5-8 have plotted their respective spectra as a series of phosphor compositions with increasing additive concentration, starting at no additive, and ending with the highest concentration of the series at 5 wt%.
• SrF 2 additive with the MgF 2 additive; in other words, a phosphor with an Sr alkaline earth and fluorine content with a phosphor having a Mg alkaline earth and fluorine content
• the phosphors have been plotted together in FIG. 9: a phosphor with no additive, a phosphor with 5 wt% SrF 2 , and a phosphor with 5 wt% gF 2 .
• the phosphor is based on the sample Lu2. iCeo.o9 l50i 2 .
• the emission spectra data in FIG. 9 has been normalized to better emphasize the effects on optical properties rendered by the inclusion the halogen and alkaline earths.
• the result illustrates that the emission peak shift to shorter wavelengths with the addition of MgF 2 and SrF 2 .
• the Lu 2 . iCe 0 0 l5O i 2 sample with no additive shows a peak emission wavelength at about 550 nm; with a 5 wt% SrF 2 additive the peak emission wavelength shifts to about 535 nm, and with a 5 wt% MgF2additive the wavelength shifts even further to about 5 10 nm,
• FIG. 10 shows how the emission wavelength of a series of exemplary Lu 2 9iCeo.o Al 5 Oi 2 phosphors decreases as the concentration of an SrF 2 additive is increased.
• Peak emission wavelength has been plotted as a function of the amount of the SrF 2 additive; samples having an SrF 2 additive content of 1 , 2, 3, and 5 wt% were tested. The results show that the peak emission wavelength was about the same for the 1 and 2 wt% samples, the wavelength being about 535 nm; as the SrF 2 additive is increased to 3 wt% the peak emission wavelength decreases to about 533 nm. With a further increase of SrF 2 additive to 5 wt% peak wavelength drops precipitously to about 524 nm.
• FIG. I I is the normalized excitation spectra of a series of exemplary Lu 2 .9 i Ceo.o9Al50i2 phosphors with different MgF 2 additive concentrations, showing that the excitation spectra becomes more narrow when the MgF 2 additive concentration is increased.
• the data shows that the present green emitting, aluminate-based phosphors exhibit a wide band of wavelengths over which the phosphors may be excited, ranging from about 380 to about 480 nm.
• the thermal stability of the present garnet phosphors is exemplified by the lutetium containing compound ⁇ iCecosAlsO with a 5wt% MgF 2 additive; its thermal stability is compared with the commercially available phosphor Ce 3+ :Y3Al50i2 in FIG. 12. It may be observed that the thermal stability of the Lu2.9iCeo 0 9Al50
• the present green emitting, aluminate-based phosphors may be used in white light il lumination systems, commonly known as "white LEDs," and in backlighting configurations for display applications.
• white light illumination systems comprise a radiation source configured to emit radiation having a wavelength greater than about 280 nm; and a halide anion-doped green aluminate phosphor configured to absorb at least a portion of the radiation from the radiation source, and emit light having a peak wavelength ranging from 480 nm to about 650 nm.
• FIG.13 shows the spectra of a white LED that includes an exemplary green-emitting, aluminate-based phosphor having the formula Lu .9iCeo . o9AlsOi 2 with a 5 wt% SrF 2 additive.
• This white LED further includes a red phosphor having the formula (Cao 2 Sr 0 S )AlSiN3:Eu 2+ .
• FIG. 14 is the spectra of a white LED with the following components: a blue InGaN LED, a green garnet having the formula Lu2 . iCeo . o AlsO
• a blue InGaN LED a green garnet having the formula Lu2 . iCeo . o AlsO
• a red nitride having the formula (Cao. 2 Sro . s)AlSiN3 :Eu 2+ or a silicate having the formula (Sro Bao 5) 2 Si0
• the sample that shows the most prominent double peak is the one labeled "EG3261 + R640," where the EG3261 designation represents the (Sro sBao s ⁇ SiG Eu 2 * phosphor, in combination with the red R640 (Cao. 2 Sro. 8 )AISiN3:Eu phosphor emitting at about 640 nm.
• the two peaks labeled LAG (3 wt% MgF 2 ) + R640 and LAG (5 wt% SrF 2 ) + R640 demonstrate a much more uniform emission of perceived white light over the wavelength range 500 to 650 nm, an attribute desirable in the art.
• FIG. 15 is the spectra of the white LED systems of FIG 14, in this instance measured at 3,000 .
• the red nitride that may be used in conjunction with the green aluminate may have the general formula (Ca,Sr)AlSiN 3 :Eu 2+ , where the red nitride may further comprise an optional halogen, and wherein the oxygen impurity content of the red nitride phosphor may be less than equal to about 2 percent by weight.
• the yellow-green silicates may have the general formula (Mg,Sr,Ca,Ba) 2 Si04:Eu 2+ , where the alkaline earths may appear in the compound either individually, or in any combination, and wherein the phosphor may be halogenated by F, CI, Br, or I (again, either individually, or in any combination).
• Tablesl & 2 A summary of exemplary data is tabulated in Tablesl & 2.
• Table 1 is the testing results of a Lu 2 .9iCeo.o9AI 5 O i2 based phosphor with three different MgF 2 additive levels.
• Table 2 tabulates the testing results of a Lu 2 .9i Ceo.o9AlsO i 2 based compound with four different SrF 2 additive.
• MgF 2 and SrF 2 additives in Lu 2 .9iCeo,o Al50i 2 shift the emission peak wavelength to shorter wavelengths, where the emission intensity is increased with increasing MgF 2 and SrF 2 concentration.
• the particle size also increases with the increasing MgF 2 and SrF 2 additive concentration.
• Table I Testing results of Lu 2 . i Ceo.o Al 5 Oi 2 with different MgF 2 levels of additive
• A is at least one of Sc, La, Gd, and Tb; B is at least one of the alkaline earths Mg, Sr, Ca, and Ba; C is at least one of the halogen elements F, C, Br, and I; and the values of the parameters x, y, z are 0 ⁇ x ⁇ 0.5; 0.001 ⁇ y ⁇ 0.2; and 0.001 ⁇ z ⁇ 0.5.
• the rare earth dopant was Gd
• the alkaline earth was either Ba or Sr.
• the halogen was F in all of the compounds tested in this series of experiments.
• a green emission will be defined as having a peak emission wavelength of from about 500 nm to about 550 nm. Emissions extending from about 550 nm to about 600 nm may be described as containing wavelengths that change from a yellow- green color to a yellow color.
• the addition of Gd doping converts the phosphor from a substantially green-emitting sample to a substantially yellow sample in the experiments described; though not shown, increasing the Gd concentration even further (from about 0.33 for Ba samples and from about 0.13 for Sr samples) shifts the emission further towards and into the yellow region of the electromagnetic spectrum.
• the halogenated aluminates in the present disclosure are defined to emit in the yellow-green to the yellow region of the electromagnetic spectrum, at wavelengths from about 550 nm to about 600 nm. Green-emitting halogenated aluminates emit at peak wavelengths ranging substantially from about 500 nm to about 550 nm. For green-emitting aluminates, see US. Pat. Application No. 13/18 1 ,226 filed July 12, 201 1 , assigned to the same assignee as the present application, and hereby incorporated herein in its entirety.
• the peak emission wavelength increased from 554 nm to 565 nm to 576 nm as the Gd amount was increased stoichiometrically from 0.07 to 0.17 to 0.33, respectively.
• the peak emission wavelength increased from 55 1 nm to 555 nm to 558 nm as the Gd amount was increased stoichiometrically from 0.03 to 0.07 to 0.13, respectively.
• FIGS. 17A-B Shown in FIGS. 17A-B are the x-ray diffraction patterns of both the Ba series and the Sr series of phosphors whose luminosity data was depicted in FIGS. 16A-B. [0094] YeHow-emittine,aluminate-based phosphors featuring terbium (Tb) and/or gadolinium (Gd).
• Tb terbium
• Gd gadolinium
• the yellow-green to yellow emitting halogenated aluminates featured the rare earth element terbium (Tb).
• Tb rare earth element
• the present inventors have conducted experiments comparing the relative effects of terbium and gadolinium in the composition where A represents at least one of Gd and Tb, either individually, or in combinations.
• Terbium is adjacent to gadolinium in the periodic table: the former (Tb) has atomic number 65, and electronic structure [Xe]4f 9 6s 2 , whereas the latter (Gd) has atomic number 64, and electronic structure [Xe]4f 7 5d6s 2 .
• the formula shows that both terbium and gadolinium substitute for the rare earth lutetium (Lu), atomic number 71 , electronic structure [Xe]4f M 5d6s 2 .
• Methods of fabricating the novel aluminate-based phosphors disclosed herein are not limited to anyone fabrication method, but may, for example, be synthesized in a three step process that includes: 1 ) blending starting materials, 2) firing the starting material mix, and 3) various processes to be performed on the fired material, including pulverizing and drying.
• the starting materials may comprise various kinds of powders, such as alkaline earth metal compounds, aluminum compounds and lutetium compounds.
• alkaline earth metal compounds include alkaline earth metal carbonates, nitrates, hydroxides, oxides, oxalates, halides, etc.
• aluminum- containing compounds include nitrates, fluorides and oxides.
• lutetium compounds include lutetium oxide, lutetium fluoride, and lutetium chloride.
• the starting materials are blended in a manner such that the desired final composition is achieved.
• the alkaline-earth, aluminum-containing compounds and lutetium compounds are blended in the appropriate ratios, and then fired to achieve the desired composition.
• the blended starting materials may be fired in a second step, and a flux may be used to enhance the reactivity of the blended materials (at any or various stages of the firing),
• the flux may comprise various kinds of halides and boron compounds, examples of which include strontium fluoride, barium fluoride, strontium chloride, barium chloride and combinations thereof.
• boron-containing flux compounds include boric acid, boric oxide, strontium borate, barium borate and calcium borate.
• the flux compound is used in amounts where the number of mole percent ranges from between about 0.01 to 0.2 mole percent, where values may typically range from about 0.01 to 0.1 mole percent, both inclusive.
• Various techniques for mixing the starting materials include, but are not limited to, using a mortar, mixing with a ball mill, mixing using a V-shaped mixer, mixing using a cross rotary mixer, mixing using a jet mill and mixing using an agitator.
• the starting materials may be either dry mixed or wet mixed, where dry mixing refers to mixing without using a solvent.
• Solvents that may be used in a wet mixing process include water or an organic solvent, where the organic solvent may be either methanol or ethanol.
• the mix of starting materials may be fired by numerous techniques known in the arl. A heater such as an electric furnace or gas furnace may be used for the firing.
• the heater is not limited to any particular type, as long as the starting material mix is fired at the desired temperature for the desired length of time.
• firing temperatures may range from about 800 to 1600° C.
• the firing time may range from about 10 minutes to 1000 hours.
• the firing atmosphere may be selected from among air, a low pressure atmosphere, a vacuum, an inert-gas atmosphere, a nitrogen atmosphere, an oxygen atmosphere and an oxidizing atmosphere.
• the compositions may be fired in a reducing atmosphere at between about 100°C to about 1600°C for between about 2 and about 10 hours.
• the phosphors disclosed herein may be prepared using a sol-gel method or a solid reaction method.
• metal nitrates are used to provide the divalent metal component of the phosphor, as well as the aluminum component of the aluminate-based phosphor.
• the metal nitrate that supplies the divalent metal component may be Ba(N0 3 )2, Mg( 0 ) 2 or Sr(N0 3 ) 2 and the metal nitrate that provides the aluminum may be A1( 0 3 ) 3 .
• This method may further include the step of using a metal oxide to provide the oxygen component of the aluminate-based phosphor.
• An example of the method includes the following steps: a) providing raw materials selected from the group consisting of Ba(N0 3 ) 2 , Mg(N0 3 )2, Ca(N0 3 ) 2l Sr(N0 3 ) 2 , ⁇ ( ⁇ 0 3 ) 3> and Lu 2 0 3 ; b) dissolving the Lu 2 0 3 in a nitric acid solution and then mixing a desired amount of the metal nitrates to form an aqueous-based nitrate solution; c) heating the solution of step b) to form a gel; d) heating the gel of step c) to between about 500° C and about 1000° C to decompose the nitrate mixture to an oxide mixture; and e) sintering the powder of step d) in a reducing atmosphere at a temperature of between about 1000° C and about 1
• Table 4 Yellow-emitting, alummate-based phosphors featuring terbium (Tb) and/or gadolinium (Gd)
• their compositions are and (Luo . ⁇ iiTbo.5Ceo.o )3Als0 1 2, respectively. They emit with the highest relative photoluminescent intensities of the compounds in Table 4, excepting YAG 1 and YAG2.
• the third composition from the top in Table 4 contains both Gd and Tb in concentrations of 0.2 and 0.3, respectively, and thus its stoichiometry is (Luo 4
• This compound, with the designation TG I emitted with a peak emission wavelength that was almost as high as (Luo xiTbo sCeo o ⁇ lsO ⁇ (555.4 nm versus 555.8 nm, respectively), although its photoluminescent intensity was not as high as either of the two compounds containing Tb only and no Gd.
• FIG. 1 8 is a plot of the photoluminescent intensity of two compounds labeled "G l " and "T l .”
• the peak emission wavelength is at about 550 nm.
• the two compounds in FIG. 19 have about the same photoluminescent intensity as the compounds in FIG. 18, but the peak emission wavelengths in FIG. 19 are shifted slightly to longer wavelengths.
• FIG. 20 Compounds with slightly longer wavelengths of emission, relative to FIGS. 19 and 18, are shown in FIG. 20.
• the upper curve in the graph corresponds to the sample labeled "TG I ,” where the Gd concentration is 0.2 and the Tb concentration is 0.3, such that the phosphor has the formula
• the lower curve in the graph corresponds to the sample labeled "G3,” where the Gd concentration is 0.5.
• This compound has no Tb, so the formula is (Luo. ⁇ j
• FIG. 21 The effect of changing either the Gd concentration or the Tb concentration in a compound having the general formula (Luo. i.xAxCeo.o )3A l50i2, is shown in FIG. 21.
• A is either Gd or Tb, but it is emphasized that according to embodiments of the present invention, Gd and Tb may be present either individually or in combinations.
• FIG. 22 The relationship between photoluminescent intensity and peak emission wavelength that the Gd-containing series of compounds have, versus the Tb-containing series of compounds, is shown in FIG. 22.
• relative photoluminescent intensity on the ordinate (y-axis) is plotted against peak emission wavelength (in nm, on the x-axis).
• peak emission wavelength in nm, on the x-axis.
• the relative photoluminescent intensity decreases as the Gd or Tb concentration increases(and, concomitantly, as the peak emission wavelength increases), with photoluminescent intensity decreasing faster in the Gd-containing series of samples than in the Tb-containing samples.
• FIG. 23 The thermal stability of exemplary Tb-containing, and Tb and Gd-containing compounds is shown in FIG. 23. Also shown for comparison are Gd-containing phosphor compounds containing Gd but no Tb.
• the CIE y chromaticity coordinate is plotted on the y-axis against the CIE x chromaticity coordinate on the x-axis.
• the data points are collected at 20 degree temperature intervals from 20 °C to 220 °C - a temperature range that includes the operating temperatures of the phosphor materials for most applications.
• the data is shown in Tables 7(i) & 7(ii).
• a shift in CIE coordinates of less than 0.005 is preferred over the temperature range tested - it is notable that only the Tb-containing materials show a shift of CIE coordinates within this range for both x and y coordinates. Specifically, only Tl , T2 and TG I exhibit the preferred temperature stability. The better temperature stability of the terbium- containing phosphor materials compared with the phosphor materials with gadolinium and no terbium is an unexpected result.
• the phosphor may comprise a cerium- activated, yellow-green to yellow-emitting aluminate-based phosphor having the formula (Lu] .
• A is at least one of Sc, La, Gd, and Tb; B is at least one of Mg, Sr, Ca, and Ba; C is at least one of F, CI, Br, and 1; 0.00 1 ⁇ x ⁇ 1.0; 0.001 ⁇ y ⁇ 0.2; and 0 ⁇ z ⁇ 0.5, and the phosphor in this embodiment contains at least some Tb.
• the phosphor comprises a cerium- activated, yellow-green to yellow-emitting aluminate-based phosphor having the formula (Lui. x A x ) 3 Al50i2:Ce, where A is at least one rare earth selected from the group consisting of Gd and Tb, either individually or in combinations; x ranges from about 0.001 to about 1.0; and the phosphor contains at least some Tb.
• the phosphor comprises a cerium- activated, yellow-green to yellow-emitting aluminate-based phosphor represented by the formula (Luo.9].
• A is at least one rare earth selected from the group consisting of Gd and Tb; and x ranges from about 0.001 to about 1 .0. As with the embodiment disclosed in the previous paragraph, this phosphor also contains at least some Tb.
• the present invention has been particularly described with reference to yellow-green to yellow emitting aluminate-based phosphors, the teaching and principles of the present invention apply also to phosphors in which the Al has been replaced, in whole or in part, by Ga, Si or Ge - for example, silicate-, galliate- and germanate-based phosphors.
• the embodiments of the phosphor materials containing halogens may have the halogen: ( 1 ) contained within the crystal substitutionally; (2) contained within the crystal interstitially; and/or (3) contained within grain boundaries that separate crystalline grains, regions and/or phases.
• the Lu aluminate materials in Table 8 have been made and tested, as described above.
• An example is provided of a representative procedure for making a compound with the formula Lu 2 0 3 (272.664 g), Ce0 2 (7.295 g), Al 2 0 3 ( 120.041 g) and a flux (20.000 g) are mixed for between 4 and 20 hours with a mixer and then added to a crucible.
• the crucible is placed into a continuous furnace and sintered at between 1500 °C and 1700 °C for between 2 and 10 hours under reduced atmosphere.
• the sintered material is converted into a powder with a crushing machine.
• a white light illumination system may comprise: an excitation source with emission wavelength within a range of 200nm to 480nm;at least one of a red-emitting phosphor or a green-emitting phosphor; and a cerium-activated, yellow-green to yellow-emitting lutetium aluminate-based phosphor comprising terbium, wherein the phosphor is configured to emit light having a peak emission wavelength ranging from about 550 nm to about 565 nm.
• the cerium-activated, yellow-green to yellow-emitting lutetium aluminate-based phosphor may be configured to absorb excitation radiation having a wavelength ranging from about 380 nm to about 480 nm. Yet furthermore, the red-emitting phosphor may have an emission wavelength within a range of 600 nm to 660 nm. Furthermore, the green-emitting phosphor may have an emission wavelength within a range of 500 nm to 545 nm. Yet furthermore, the red-emitting phosphor may be a nitride.
• the nitride may be at least one of (Ca,Sr)AISiN 3 :Eu 2+ , (Ca,Sr) 2 N 5 N 8 :Eu 2+ , and (Ca,Sr)AlSi 4 N 7 :Eu 2+ .
• the green-emitting phosphor may be a silicate.
• the silicate may have the formula (Sr,Ba, g) 2 Si0 4 :Eu 2+ .

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• 2012
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