SMOOTHING PHOSPHORS FOR AC LED LIGHTING

Abstract

Disclosed are smoothing phosphors for AC LED lighting that are capable of prolonging the light emission time of an AC LED (or array of AC LEDs) during a cycle response to a phase change of the alternating current to substantially reduce flicker. The smoothing phosphor of the present teachings comprises a matrix represented by the formula: M.sub.(l-k-r-v)X.sub.(m-p)Al.sub.2(n-0.5x-0.5y)O.sub.3(n-0.5x-0.5y): Mn.sub.(x+p)O.sub.(x+p), Si.sub.yO.sub.2y, Eu.sub.k, R.sub.r, Li.sub.v wherein M is at least one of La.sub.2O.sub.3, Ce.sub.2O.sub.3, Gd.sub.2O.sub.3, Lu.sub.2O.sub.3, Ba.sub.2OF.sub.2, Sr.sub.2OF.sub.2, Ca.sub.2OF.sub.2, Ba.sub.2OCl.sub.2, Sr.sub.2OCl.sub.2, Ca.sub.2OCl.sub.2, BaO, SrO, CaO, or ZnO; provided that when M comprises BaO, SrO, CaO, or ZnO, M does not comprise La.sub.2O.sub.3, Ce.sub.2O.sub.3, Gd.sub.2O.sub.3, Lu.sub.2O.sub.3, Ba.sub.2OF.sub.2, Sr.sub.2OF.sub.2, Ca.sub.2OF.sub.2, Ba.sub.2OCl.sub.2, Sr.sub.2OCl.sub.2, or Ca.sub.2OCl.sub.2; X is at least one of MgO or ZnO; R is at least one of Sm, Pr, Tb, Dy, Er, or Ho; m=0 to 2; n=4 to 11; x=0.005 to 1; y=0.005 to 1; p=0 to 1; k=0 to 0.2; r=0 to 0.2; and v=0 to 0.2.

Claims

1. A smoothing phosphor for AC LED lighting, said smoothing phosphor comprising a matrix represented by the formula: M.sub.(l-k-r-v)X.sub.(m-p)Al.sub.2(n-0.5x-0.5y):O.sub.3(n-0.5x-0.5y):Mn.sub.(x+p)O.sub.(x+p), Si.sub.yO.sub.2y, Eu.sub.k, R.sub.r, Li.sub.v wherein: M is at least one of La.sub.2O.sub.3, Ce.sub.2O.sub.3, Gd.sub.2O.sub.3, Lu.sub.2O.sub.3, Ba.sub.2OF.sub.2, Sr.sub.2OF.sub.2, Ca.sub.2OF.sub.2, Ba.sub.2OCl.sub.2, Sr.sub.2OCl.sub.2, Ca.sub.2OCl.sub.2, BaO, SrO, CaO, or ZnO; provided that when M comprises BaO, SrO, CaO, or ZnO, M does not comprise La.sub.2O.sub.3, Ce.sub.2O.sub.3, Gd.sub.2O.sub.3, Lu.sub.2O.sub.3, Ba.sub.2OF.sub.2, Sr.sub.2OF.sub.2, Ca.sub.2OF.sub.2, Ba.sub.2OCl.sub.2, Sr.sub.2OCl.sub.2, or Ca.sub.2OCl.sub.2; X is at least one of MgO or ZnO; R is at least one of Sm, Pr, Tb, Dy, Er, or Ho; m=0 to 2; n=4 to 11; x=0.005 to 1; y=0.005 to 1; p=0 to 1; k=0 to 0.2; r=0 to 0.2; and v=0 to 0.2.

2. The smoothing phosphor of claim 1, wherein M is at least one of La.sub.2O.sub.3, Ce.sub.2O.sub.3, Gd.sub.2O.sub.3, Lu.sub.2O.sub.3, Ba.sub.2OF.sub.2, Sr.sub.2OF.sub.2, Ca.sub.2OF.sub.2, Ba.sub.2OCl.sub.2, Sr.sub.2OCl.sub.2, or Ca.sub.2OCl.sub.2, m=0, n=11, and p=0, and the matrix is represented by the formula: M.sub.l-k-r)Al.sub.(22-x-y)O.sub.(33-1.5x-1.5y):Mn.sub.xO.sub.x, Si.sub.yO.sub.2y, Eu.sub.k, R.sub.r, Li.sub.v.

3. The smoothing phosphor of claim 1, wherein M is at least of BaO, SrO, CaO, or ZnO, m=2, n=8, and the matrix is represented by the formula: M.sub.(l-k-r-v)X.sub.(2-p)Al(.sub.16-x-y)O.sub.(24-1.5x-1.5y):Mn.sub.(x+p)O.sub.(x+p), Si.sub.yO.sub.2y, Eu.sub.k, R.sub.r, Li.sub.v.

4. The smoothing phosphor of claim 1, wherein M is at least of BaO, SrO, CaO, or ZnO, m=1, n=5, and the matrix is represented by the formula: M.sub.(l-k-r-v)X.sub.(l-p)Al.sub.(10-x-y))O.sub.(15-1.5x-1.5y):Mn.sub.x+p)O.sub.(x+p), Si.sub.yO.sub.2y, Eu.sub.k, R.sub.r, Li.sub.v.

5. The smoothing phosphor of claim 1, wherein M is at least of BaO, SrO, CaO, or ZnO, m=1, n=7, and the matrix is represented by the formula: M.sub.(l-k-r-v)X.sub.(l-p)Al.sub.(14-x-y)O.sub.(21-1.5x-1.5y):Mn.sub.(x+p)O.sub.(x+p), Si.sub.yO.sub.2y, Eu.sub.k, R.sub.r, Li.sub.v.

6. The smoothing phosphor of claim 1, wherein M is at least of BaO, SrO, CaO, or ZnO, m=0, n=6, p=0, and the matrix is represented by the formula: M.sub.(l-k-r-v)Al.sub.(12-x-y)O.sub.(18-1.5x-1.5y):Mn.sub.xO.sub.x, Si.sub.yO.sub.2y, Eu.sub.k, R.sub.r, Li.sub.v.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The present teachings are illustratively shown and described in reference to the accompany drawings, in which

[0007] FIG. 1 shows the emission and excitation spectra of LaAl.sub.11O.sub.18:Mn.sub.0.15, showing that La.sup.3+ aluminate compounds are suitable hosts for Mn.sup.2+ for use as smoothing phosphors in blue AC LED lighting applications;

[0008] FIG. 2 shows the emission and excitation spectra (a) of an exemplary smoothing phosphor represented by the formula LaAl.sub.11O.sub.18:Mn.sub.0.20, Si.sub.0.20, compared to the excitation and emission spectra (b) of LaAl.sub.11O.sub.18:Mn.sub.0.20 to illustrate the impact of charge compensation with Si.sup.4+;

[0009] FIG. 3 shows a series of emission spectra of exemplary smoothing phosphors represented by the formula LaAl.sub.11O.sub.18:Mn.sub.x, Si.sub.y, where the Mn.sup.2+ content, x, and the Si.sup.4+ content, y, was varied as follows, x=y=0.075, 0.175, 0.20, 0.275, 0.30, 0.35, and 0.425, to investigate the role that Mn.sup.2+content has on emission intensity;

[0010] FIG. 4 shows the excitation and emission spectra of an exemplary smoothing phosphor having the formula LaAl.sub.11O.sub.18:Mn.sub.0.425, Si.sub.0.425 to illustrate the red emission bands produced from Mn-Mn pairs;

[0011] FIG. 5 shows the excitation and emission spectra of an exemplary smoothing phosphor having the formula LaAl.sub.11O.sub.18:Mn.sub.0.30, Si.sub.0.30, SI.sub.0.03 to illustrate the effect of further co-doping with Sm.sup.3+;

[0012] FIG. 6 shows the excitation and emission spectra of an exemplary smoothing phosphor having the formula LaAl.sub.11O.sub.18:Mn.sub.0.30, Si.sub.0.30, EU.sub.0.10 to investigate the impact on excitation intensity of Mn.sup.2+ emission with the further co-doping of Eu.sup.2+;

[0013] FIG. 7 shows the emission and excitation spectra of an exemplary smoothing phosphor having the formula CeAl.sub.11O.sub.18:Mn.sub.0.28, Si.sub.0.28;

[0014] FIG. 8A shows the emission and excitation spectra of an exemplary smoothing phosphor having the formula BaAl.sub.11O.sub.17F:Mn.sub.0.30, Si.sub.0.30;

[0015] FIG. 8B shows the emission and excitation spectra of an exemplary smoothing phosphor having the formula BaAl.sub.11O.sub.17F:Mn.sub.0.30, Si.sub.0.30, Eu.sub.0.06;

[0016] FIG. 9 shows the emission and excitation spectra of an exemplary smoothing phosphor having the formula BaAl.sub.11O.sub.17Cl:Mn.sub.0.30, Si.sub.0.30;

[0017] FIG. 10 shows the emission and excitation spectra of an exemplary smoothing phosphor having the formula Ba.sub.0.5Ca.sub.0.5Al.sub.11O.sub.17F:Mn.sub.0.20, Si.sub.0.20;

[0018] FIG. 11 shows the emission and excitation spectra of an exemplary smoothing phosphor having the formula BaMg.sub.2Al.sub.16O.sub.27:Mn.sub.0.85, Si.sub.0.28;

[0019] FIG. 12 shows the emission and excitation spectra of an exemplary smoothing phosphor having the formula BaMg.sub.2Al.sub.16O.sub.27:Mn.sub.0.85, Si.sub.0.28, Eu.sub.0.10;

[0020] FIG. 13 shows the emission and excitation spectra of an exemplary smoothing phosphor having the formula BaAl.sub.12O.sub.19:Mn.sub.0.30, Si.sub.0.30; and

[0021] FIG. 14 shows the emission and excitation spectra of an exemplary smoothing phosphor having the formula SrAl.sub.12O.sub.19:Mn.sub.0.30, Si.sub.0.30.

DETAILED DESCRIPTION OF THE INVENTION

[0022] The present teachings are directed to the creation of smoothing phosphors for AC LED lighting that are capable of reducing flicker of an AC LED (or array of LEDs). The smoothing phosphor of the present teachings comprises a matrix represented by the general formula: M.sub.(l-k-r-y)X.sub.(m-p)Al.sub.2(n-0.5x-0.5y)O.sub.3(n-0.5x-0.5y):Mn.sub.(x+p)O.sub.(x+p), Si.sub.yO.sub.2y, EU.sub.k, R.sub.r, Li.sub.v, wherein M is at least one of La.sub.2O.sub.3, Ce.sub.2O.sub.3, Gd.sub.2O.sub.3, Lu.sub.2O.sub.3, Ba.sub.2OF.sub.2, Sr.sub.2OF.sub.2, Ca.sub.2OF.sub.2, Ba.sub.2OCl.sub.2, Sr.sub.2OCl.sub.2, Ca.sub.2OCl.sub.2, BaO, SrO, CaO, or ZnO; provided that when M comprises BaO, SrO, CaO, or ZnO, M does not comprise La.sub.2O.sub.3, Ce.sub.2O.sub.3, Gd.sub.2O.sub.3, Lu.sub.2O.sub.3, Ba.sub.2OF.sub.2, Sr.sub.2OF.sub.2, Ca.sub.2OF.sub.2, Ba.sub.2OCl.sub.2, Sr.sub.2OCl.sub.2, or Ca.sub.2OCl.sub.2; X is at least one of MgO or ZnO; R is at least one of Sm, Pr, Tb, Dy, Er, or Ho; m=0 to 2; n=4 to 11; x=0.005 to 1; y=0.005 to 1; p=0 to 1; k=0 to 0.2; r=0 to 0.2; and v=0 to 0.2.

[0023] When an LED (or array of LEDs) are directly pumped or operated from AC, typically 110V/60 Hz or 230V/50 Hz, the instantaneous AC voltage applied has to exceed a minimum threshold value in order for current to flow through the LED (or array of LEDs), making the LED turn on and emit light. Given the AC LED (or array of AC LEDs) minimum threshold value, along with the sinusoidal waveform of AC, the AC LED turns on and off at the same frequency, causing the AC LED (or array of AC LEDs) to flicker when directly connected to an AC power source, thereby affecting the observed quality of light produced.

[0024] Flicker is the periodic change in the instantaneous light output of a light source. Flicker is measured using two different metrics, i.e. percent flicker and flicker index. Percent flicker, sometimes referred to as modulation index, is defined as the ratio of the maximum light intensity output value minus the minimum light intensity output value divided by the sum of the maximum and minimum light intensity output values for one AC cycle. Flicker index is defined as the ratio of the area under the light intensity output curve above the average light intensity output value to the total area of the light intensity output curve for one AC cycle. Although both metrics for flicker measurement are relative measures of the cyclic variation in light output of a light source, percent flicker does not take into account the waveform of the light source, nor the duty cycle, whereas flicker index does. Nonetheless, the presence of flicker can substantially impact the quality of light produced and thus perceived by a human observer.

[0025] By employing smoothing phosphors in accordance with the present invention, the light emission time of the AC LED (or array of LEDs) is prolonged during a cycle response to a phase change of the AC such that flicker can be reduced. Generally speaking, an AC LED operating at 50 to 120 Hz has an off period that is normally about 1 ms to about 10 ms. When a smoothing phosphor is used, the AC LED continues to emit light during this off period such that the flicker, otherwise produced, is substantially minimized. In order for a smoothing phosphor to be effective in the reduction of flicker of an AC LED, the smoothing phosphor should have an emission lifetime that is substantially similar to the off period of the AC LED. Ions having such an emission lifetime include Mn.sup.2+, Fe.sup.3+, 4f rare earth ions, or ions with s electrons in the out-shell, such as Bi.sup.3+ (6s.sup.2), Tl.sup.+ (6s.sup.2), Sb.sup.3+ (5s.sup.2), S.sub.n.sup.2+ (5.sub.s.sup.2), all of which involve spin-forbidden transitions, and thus provide a longer lifetime of emission. However, based on the emission spectrum of an AC LED, along with additional requirements for practical applications of AC LED lighting, Fe.sup.3+, 4f rare earth ions, or ions with s electrons in the out-shell are not suitable.

[0026] In general, Mn.sup.2+ ions emit light that is characteristically in the green or red region of the electromagnetic spectrum. Mn.sup.2+ has 5 electrons in its 3d shell, labeled as 3d.sup.5. The ground state of Mn.sup.2+ is S-state with zero total orbital angular momentum, total spin 5/2, and the spin multiplet, indicated as a superscript, of 6, thus labeled as .sup.6S.sub.0. The first excited state of free Mn.sup.2+ ions is .sup.4G. Above .sup.4G, are .sup.4P, .sup.4D, .sup.2I, .sup.4F, .sup.2D, etc. In the cubic crystal field, .sup.6S.sub.0 is represented as .sup.6A.sub.1. The excited state .sup.4G, having 9-fold orbital degeneracy, is split into .sup.4T.sub.1, .sup.4T.sub.2, .sup.4E, and .sup.4A.sub.1 in the cubic representation. A is an orbital singlet, E is a doublet, and Ts are triplets. It can be noticed that all spin-multiplets (S=4 or 2) of excited states are different from the ground state (S=6). Therefore, all the electronic transitions of Mn.sup.2+ are spin forbidden and thus illustrate an emission lifetime of Mn.sup.2+ that is substantially similar to the off period of an AC LED (or array of AC LEDs).

[0027] Furthermore, this also implies that the electronic transition probability of Mn.sup.2+ is relatively low, and thus the excitation of Mn.sup.2+ with that of AC LED emission is weaker than that of a spin allowed transition. To aid in the excitation of Mn.sup.2+ with that of AC LED emission, a host matrix with strong absorption of AC LED emission through Mn.sup.2+ was investigated. In addition, the host matrix should also entail a strong, broad, efficient emission in the spectral emission range of Mn.sup.2+, an emission lifetime that is also substantially similar to the off period of the AC LED, and have a high concentration quenching onset level of the emissive Mn.sup.2+ ions. In light of the foregoing characteristics, it was determined that suitable host matrices for Mn.sup.2+ is that of aluminate-based compounds having the general formula: M.sub.(l-k-r-v)X.sub.(m-p)Al.sub.2(n-0.5x-0.5y)O.sub.3(n-0.5x-0.5y), wherein M is at least one of La.sub.2O.sub.3, Ce.sub.2O.sub.3, Gd.sub.2O.sub.3, Lu.sub.2O.sub.3, Ba.sub.2OF.sub.2, Sr.sub.2OF.sub.2, Ca.sub.2OF.sub.2, Ba.sub.2OCl.sub.2, Sr.sub.2OCl.sub.2, Ca.sub.2OCl.sub.2, BaO, SrO, CaO, or ZnO; provided that when M comprises BaO, SrO, CaO, or ZnO, M does not comprise La.sub.2O.sub.3, Ce.sub.2O.sub.3, Gd.sub.2O.sub.3, Lu.sub.2O.sub.3, Ba.sub.2OF.sub.2, Sr.sub.2OF.sub.2, Ca.sub.2OF.sub.2, Ba.sub.2OCl.sub.2, Sr.sub.2OCl.sub.2, or Ca.sub.2OCl.sub.2; X is at least one of MgO or ZnO; m=0 to 2; n=4 to 11; x=0.005 to 1; y=0.005 to 1; p=0 to 1; k=0 to 0.2; r=0 to 0.2; and v=0 to 0.2. These suitable host matrices have hexagonal symmetry and contain Al-O spinel blocks, in which Al.sup.3+ occupies either tetrahedral or octahedral sites of the spinel blocks. Thus, when doped with Mn.sup.2+, M.sup.3+ of the host matrix is partially or fully replaced with that of Mn.sup.2+.

[0028] FIG. 1 shows the excitation and emission spectrum of LaAl.sub.11O.sub.18:Mn.sub.0.15under 450 nm blue LED excitation, in which all excitation peaks are labeled in cubic field representations. The excitation is strong at around 450 nm with spectral width at around 20 nm and the peak of the emission is at around 520 nm, which is characteristically in the green region of the electromagnetic spectrum. This shows that certain Mn.sup.2+ doped aluminate phosphors are suitable for use in blue AC LED lighting applications.

[0029] It was further determined that the Mn.sup.2+ doped aluminate phosphors, possess a charge defect as a result of the oxygen vacancies created by the partial or full substitution of Mn.sup.2+ for that of Al.sup.3+. A charge defect refers to defects in the crystalline matrix of a phosphor as a result of the replacement, partial or full, of one atom for another in the matrix that is not an exact match in charge (valence state), thereby resulting in altered photoluminescent characteristics, such as e.g., decrease of emission intensity. Thus, in order to minimize the charge defects produced by such substitution, the smoothing phosphors of the present teachings are also further co-doped with Si.sup.4+. As an example, FIG. 2 shows the excitation and emission spectra (a) of an exemplary smoothing phosphor represented by the formula LaAl.sub.11O.sub.18:Mn.sub.0.20, Si.sub.0.20 compared to the excitation and emission spectra (b) of LaAl.sub.11O.sub.18:Mn.sub.0.20 under 450 nm blue LED excitation, to investigate the effect the incorporation of Si.sup.4+ has on emission intensity. The emission intensity of LaAl.sub.11O.sub.18:Mn.sub.0.20, Si.sub.0.20 is more than approximately 20% greater than that of LaAl.sub.11O.sub.18:Mn.sub.0.20. This further illustrates the impact the presence of charge defect(s) within the crystalline matrix of a phosphor has on emission intensity and the effectiveness of charge compensation.

[0030] The concentration of Mn.sup.2+ within the smoothing phosphor should be as a high as possible to maximize the excitation intensity of Mn.sup.2+. However with too high Mn.sup.2+ content, concentration quenching can occur, thereby reducing the emission intensity of the smoothing phosphor. Thus, there is a balance that exists between the excitation intensity, the emission intensity, and Mn.sup.2+ content of the smoothing phosphor. The role that Mn.sup.2+ content has on the emission intensity of the smoothing phosphors of the present teachings was investigated. FIG. 3 depicts a series of emission spectra of exemplary smoothing phosphors represented by the formula LaAl.sub.11O.sub.18:Mn.sub.x, Si.sub.r, under 450 nm blue LED excitation, where the Mn.sup.2+ content, x, and the Si.sup.4+ content, y, was varied as follows, x=y=0.075, 0.175, 0.20, 0.275, 0.30, 0.35, and 0.425. As illustrated in FIG. 3, the maximum emission intensity reached before concentration quenching occurs is shown to be at a Mn.sup.2+ content of about 0.30 mols. Furthermore, as shown in FIG. 3, as concentration quenching begins to occur, a decrease in emission intensity results.

[0031] FIG. 4 is the excitation and emission spectra of an exemplary smoothing phosphor having the formula LaAl.sub.11O.sub.18:Mn.sub.0.425, Si.sub.0:425. As seen in FIG. 4, at a Mn.sup.2+ content of about 0.425 mol, the emission peak at about 675 nm becomes strong and broad, which can be beneficial in white lighting applications. The emission intensity increases nonlinearly and rapidly with Mn.sup.2+ content. Therefore, the emission of Mn.sup.2+ in the red region of the electromagnetic spectrum is not due to other high field sites, but rather is presumably due to Mn-Mn pairs. The number of pairs should increase as squared concentration. It should be noted that in some instances where the contribution of Mn.sup.2+ emission in the red region of the electromagnetic spectrum is considered, concentration quenching resulting in the reduction of emission intensity at about 520 nm may not substantially impact the overall emission intensity of the smoothing phosphor. Furthermore, it should be noticed that the excitation spectrum of the red emission band is similar to the excitation spectrum of single Mn.sup.2+ ions, and therefore indicates that the emission of the Mn-Mn pairs results from the energy transfer through single-Mn.sup.2+ ions, along with having an emission lifetime as long as single-Mn.sup.2+ ions.

[0032] Alternatively or in addition to the Mn-Mn pairs emission, the smoothing phosphors of the present teachings may also emit light in the red region of the electromagnetic spectrum with the further co-doping of rare earths such as Sm.sup.3+, Tb.sup.3+, Dy.sup.3+, Er.sup.3+, or Ho.sup.3+. For example, FIG. 5 illustrates the excitation and emission spectra of an exemplary smoothing phosphor having the formula LaAl.sub.11O.sub.18:Mn.sub.0.30, Si.sub.0.30, Sm.sub.0.03. As seen in FIG. 5, the presence of Sm.sup.3+ adds three narrow emission peaks at around 560 nm, 598 nm, and 645 nm. It should be noted that the excitation spectrum monitoring at Sm.sup.3+ emission peaks is similar to that of the Mn.sup.2+ excitation spectrum, thereby implying that the Sm.sup.3+ emission results from energy transfer from Mn.sup.2+, along with the Sm.sup.3+ emission lifetime being substantially similar to the emission lifetime of Mn.sup.2+. In other words, Sm.sup.3+ not only contributes to the smoothing phosphors emission of light in the red region of the electromagnetic spectrum, which is beneficial in white lighting applications, but also to the reduction of flicker of an AC driven LED (or array of LEDs). It should be noted that in some instances, the smoothing phosphors of the present teachings may also be further co-doped with Li.sup.+ to function as a charge compensator for the charge defect that may result with the presence of Sm.sup.3+.

[0033] In another aspect of the present teachings, the smoothing phosphors may be further co-doped with Eu.sup.2+ so as to enhance the excitation intensity, and thus the emission intensity, of Mn.sup.2+. The emission spectrum of Eu.sup.2+ overlaps with the excitation spectrum of Mn.sup.2+, therefore it is possible through energy transfer from Eu.sup.2+ to Mn.sup.2+ to increase excitation in the spectral range of about 360 to 410 nm of the smoothing phosphors of the present teachings. As an example, FIG. 6 illustrates the excitation and emission spectra of an exemplary smoothing phosphor having the formula LaAl.sub.11O.sub.18:Mn.sub.0.30, Si.sub.0.30, Eu.sub.0.10 under 450 nm blue LED excitation. As shown in FIG. 6, the energy transfer that occurs between Eu.sup.2+ and Mn.sup.2+ is efficient, thereby increasing the excitation intensity of the Mn.sup.2+ emission in the spectral range of about 365-380 nm. This increase of Mn.sup.2+ excitation intensity indicates that such material is an exemplary smoothing phosphor that is also suitable for use in UV AC LED lighting applications.

[0034] Other exemplary smoothing phosphors in accordance with the present teachings are illustrated in FIGS. 7-10, in which La.sub.2O.sub.3 is partially or fully replaced with at least one of Ce.sub.2O.sub.3, Gd.sub.2O.sub.3, Lu.sub.2O.sub.3, Ba.sub.2OF.sub.2, Sr.sub.2OF.sub.2, Ca.sub.2OF.sub.2, Ba.sub.2OCl.sub.2, Sr.sub.2OCl.sub.2, or Ca.sub.2OCl.sub.2. FIG. 7 shows the emission and excitation spectra of an exemplary smoothing phosphor having the formula CeAl.sub.11O.sub.18:Mn.sub.0.28, Si.sub.0.28 under 450 nm blue LED excitation. The strong excitation peak at about 310 nm originates from Ce.sup.3+5d transition. Since this excitation peak appears in the excitation spectrum of Mn.sup.2+ emission, energy transfer from Ce.sup.3+ to Mn.sup.2+ is indicated. Furthermore, when such smoothing phosphor was pumped at the excitation peak of Ce.sup.3+ at about 310 nm, the residual weak emission from Ce.sup.3+ that results also indicates that energy transfer from Ce.sup.3+ to Mn.sup.2+ occurred. FIG. 8A shows the emission and excitation spectra of an exemplary smoothing phosphor having the formula BaAl.sub.11O.sub.17F:Mn.sub.0.30, Si.sub.0.30 under 450 nm blue LED excitation. It can be seen that a strong excitation peak appears at about 450 nm which is similar to the exemplary smoothing phosphor lanthanum aluminate co-doped with Mn.sup.2+ and Si.sup.4+. FIG. 8B shows the emission and excitation spectra of an exemplary smoothing phosphor having the formula BaAl.sub.11O.sub.17F:Mn.sub.0.30, Si.sub.0.30, Eu.sub.0.06 under 450 nm blue LED excitation. It can be seen that a strong excitation peak appears at about 330 nm, and strong energy transfer from Eu.sup.2+ to Mn.sup.2+ occurs. FIG. 9 shows the emission and excitation spectra of an exemplary smoothing phosphor having the formula BaAl.sub.11O.sub.17Cl:Mn.sub.0.30, Si.sub.0.30 under 450 nm blue LED excitation. FIG. 10 shows the emission and excitation spectra of an exemplary smoothing phosphor having the formula Ba.sub.0.5Ca.sub.0.5Al.sub.11O.sub.17F:Mn.sub.0.20, Si.sub.0.20 under 450 nm blue LED excitation.

[0035] Other exemplary smoothing phosphors in accordance with the present teachings are illustrated in FIGS. 11-14, in which La.sub.2O.sub.3 is fully replaced with at least one of BaO, SrO, CaO, or ZnO. In other words, in instances where at least one of BaO, SrO, CaO or ZnO is incorporated into the host matrix of the smoothing phosphor of the present teachings, La.sub.2O.sub.3, Ce.sub.2O.sub.3, Gd.sub.2O.sub.3, Lu.sub.2O.sub.3, Ba.sub.2OF.sub.2, Sr.sub.2OF.sub.2, Ca.sub.2OF.sub.2, Ba.sub.2OCl.sub.2, Sr.sub.2OCl.sub.2, or Ca.sub.2OCl.sub.2 are not present within the host matrix. FIG. 11 shows the emission and excitation spectra of an exemplary smoothing phosphor having the formula BaMg.sub.2Al.sub.16O.sub.27:Mn.sub.0.85, Si.sub.0.28 under 450 nm blue LED excitation. The emission peak is located at about 520 nm, which is similar to the exemplary smoothing phosphor lanthanum aluminate co-doped with Mn.sup.2+ and Si.sup.4+, and the excitation peak at about 450 nm remains strong, but a broad and strong excitation band of Mn.sup.2+ is at about 330 nm. FIG. 12 shows the emission and excitation spectra of an exemplary smoothing phosphor having the formula BaMg.sub.2Al.sub.16O.sub.27:Mn.sub.0.85, Si.sub.0.28, Eu.sub.0.10 under 450 nm blue LED excitation. It can be seen that a strong and broad excitation band of Eu.sup.2+ overlaps with the Mn.sup.2+ excitation band of about 330 nm and extends to about 410 nm. The emission peak at about 520 nm is measured by pumping the overlapped band at about 400 nm. Thus, when compared to the excitation peak of Mn.sup.2+ at about 450 nm, the intensity of the emission peak indicates that the energy transfer from Eu.sup.2+ to Mn.sup.2+ contributes to most of the emission of the Mn.sup.2+ ions. This increase of Mn.sup.2+ excitation intensity indicates that such exemplary smoothing phosphor is also suitable for use in UV AC LED lighting applications. FIG. 13 shows the emission and excitation spectra of an exemplary smoothing phosphor having the formula BaAl.sub.12O.sub.19:Mn.sub.0.30, Si.sub.0.30 under 450 nm blue LED excitation. The strongest excitation peak is located at about 450 nm, which is similar to the smoothing phosphor lanthanum aluminate co-doped with Mn.sup.2+ and Si.sup.4+. FIG. 14 shows the emission and excitation spectra of an exemplary smoothing phosphor having the formula SrAl.sub.12.sup.O.sub.19:Mn.sub.0.30, Si.sub.0.30 under 450 nm blue LED excitation. Similar to that of FIG. 13, the strongest excitation peak of this exemplary smoothing phosphor is located at about 450 nm.

[0036] A number of methods may be used to synthesize the smoothing phosphors of the present teachings such as, liquid mixing methods, solid chemical reaction methods, etc. Liquid mixing methods include methods such as co-precipitation and sol-gel techniques. In solid chemical reaction methods, a flux, such as H.sub.3BO.sub.3 or B.sub.2O.sub.3, is used to stimulate the solid chemical reaction. A solid chemical reaction method may include admixing various starting materials in a predetermined ratio and pre-sintering them in a furnace, followed by grinding and sintering in the furnace at a higher temperate. For example in instances of lab scale, one method may include weighing the starting materials of the smoothing phosphor into a weighing dish, followed by admixing the materials and grinding into a mortar with a pestle until uniform. The ground material is then placed in an alumina combustion boat and placed in an oven at around 900 C. in air or in a forming gas mixture of 97% N.sub.2, and 3% H.sub.2 at a rate of 50 cm.sup.3/min for four hours. The material is then cooled and ground again in a mortar with a pestle, followed by again placing the material into an alumina combustion boat and sintered at around 1350 C. to 1450 C. for four hours in the forming gas mixture of 97% N.sub.2 and 3% H.sub.2 at a rate of 50 cm.sup.3/min. The material is then cooled and ground to a powder of the desired particle size to yield a smoothing phosphor in accordance with the present teachings.

[0037] For the purposes of describing and defining the present teachings, it is noted that the term substantially is utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement or other representation. The term substantially is also utilized herein to present the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.

[0038] Although the teachings have been described with respect to various embodiments, it should be realized that these teachings are also capable of a wide variety of further and other embodiments within the spirit and scope of the appended disclosure.