Patent Description:
Light emitting diodes based on luminescent materials are known in the art. <CIT> describes a blue-green illumination system, including a semiconductor light emitter, and a luminescent material, wherein the system has an emission with CIE color coordinates located within an area of a of a pentagon on a CIE chromaticity diagram, whose corners have the following CIE color coordinates: i) x=<NUM> and y=<NUM>; ii) x=<NUM> and y=<NUM>; iii) x=<NUM> and y=<NUM>; iv) x=<NUM> and y=<NUM>; and v) x=<NUM> and y=<NUM>. The luminescent material includes two or more phosphors. The illumination system may be used as the green light of a traffic light or an automotive display.

<NPL>, describes the synthesis and characterization of green Zn-Ag-In-S and red Zn-Cu-In-S quantum dots for ultrahigh color quality of down-converted white LEDs.

<NPL>, describes oxo- and (oxo)nitridoberyllates as host lattices for application in illumination grade phosphor converted (pc)LEDs having narrow-band emission upon doping with Eu<NUM>+.

Semiconductor light emitting diodes and laser diodes (collectively referred to herein as "LEDs") are among the most efficient light sources currently available. The emission spectrum of an LED typically exhibits a single narrow peak at a wavelength determined by the structure of the device and by the composition of the semiconductor materials from which it is constructed. By suitable choice of device structure and material system, LEDs may be designed to operate at ultraviolet, visible, or infrared wavelengths.

LEDs may be combined with one or more wavelength converting materials (generally referred to herein as "phosphors") that absorb light emitted by the LED and in response emit light of a longer wavelength. For such phosphor-converted LEDs ("pcLEDs"), the fraction of the light emitted by the LED that is absorbed by the phosphors depends on the amount of phosphor material in the optical path of the light emitted by the LED, for example on the concentration of phosphor material in a phosphor layer disposed on or around the LED and the thickness of the layer.

Phosphor-converted LEDs may be designed so that all of the light emitted by the LED is absorbed by one or more phosphors, in which case the emission from the pcLED is entirely from the phosphors. In such cases the phosphor may be selected, for example, to emit light in a narrow spectral region that is not efficiently generated directly by an LED.

Alternatively, pcLEDs may be designed so that only a portion of the light emitted by the LED is absorbed by the phosphors, in which case the emission from the pcLED is a mixture of light emitted by the LED and light emitted by the phosphors. By suitable choice of LED, phosphors, and phosphor composition, such a pcLED may be designed to emit, for example, white light having a desired color temperature and desired color-rendering properties.

The present invention provides a light emitting device comprising:.

In the present invention, the optical output from the light emitting device, formed from the light emitted by the one or more phosphors, has an x,y color point with x < <NUM> and <NUM> < y < <NUM> in the <NUM> CIE color space.

In embodiments of the light emitting device, the combined phosphor emission spectrum has an x,y color point in the <NUM> CIE color space that does not satisfy x < <NUM> and <NUM> < y < <NUM>; and the optical output from the light emitting device comprises blue light from the LED that shifts the x,y color point of the optical output of the light emitting device from that of the combined phosphor emission spectrum to a color point for which x < <NUM> and <NUM> < y < <NUM>.

In embodiments of the light emitting device, the x,y color point of the optical output from the light emitting device does not comprise blue light emitted by the LED. In embodiments of the light emitting device, the one or more phosphors comprise a Sr<NUM>Al<NUM>O<NUM>:Eu<NUM>+ phosphor. In embodiments of the light emitting device, the one or more phosphors comprise only a Sr<NUM>Al<NUM>O<NUM>:Eu<NUM>+ phosphor and no other phosphors. In embodiments of the light emitting device, wherein the LED is or comprises an AlInGaN light emitting diode. In embodiments of the light emitting device: an optical output from the light emitting device, formed from the light emitted by the one or more phosphors and optionally including blue light from the LED, has an x,y color point with x < <NUM> and <NUM> < y < <NUM> in the <NUM> CIE color space; the LED is or comprises an AlInGaN light emitting diode; and the one or more phosphors comprise a Sr<NUM>Al<NUM>O<NUM>:Eu<NUM>+. In embodiments of the light emitting device, the one or more phosphors comprise only a Sr<NUM>Al<NUM>O<NUM>:Eu<NUM>+ phosphor and no other phosphors. In embodiments of the light emitting device: the LED is or comprises an AlInGaN light emitting diode; an optical output from the light emitting device is formed from the light emitted by the one or more phosphors and a blue light component emitted by the LED; the combined phosphor emission spectrum has an x,y color point in the <NUM> CIE color space that does not satisfy x < <NUM> and <NUM> < y < <NUM>; and the blue light component of the optical output from the light emitting device shifts the x,y color point of the optical output of the light emitting device from that of the combined phosphor emission spectrum to a color point for which x < <NUM> and <NUM> < y < <NUM>.

In yet a further aspect the invention provides a method of signaling the autonomous driving state of an automobile, the method comprising:.

In embodiments of the method, the LED is or comprises an AlInGaN light emitting diode. In embodiments of the method, the one or more phosphors comprise a Sr<NUM>Al<NUM>O<NUM>:Eu<NUM>+ phosphor. In embodiments of the method, the one or more phosphors comprise only a Sr<NUM>Al<NUM>O<NUM>:Eu<NUM>+ phosphor and no other phosphors. In embodiments of the method, the combined phosphor emission spectrum has an x,y color point in the <NUM> CIE color space that does not satisfy x < <NUM> and <NUM> < y < <NUM>; and the optical output from the light emitting device is formed from the light emitted by the one or more phosphors and a blue light component emitted by the LED; the blue light component of the optical output from the light emitting device shifts the x,y color point of the optical output of the light emitting device from that of the combined phosphor emission spectrum to a color point for which x < <NUM> and <NUM> < y < <NUM>.

In embodiments of the method, the light emitting device comprises the light emitting device as further defined herein (such as e.g. defined in claim <NUM>).

In specific embodiments, the one or more phosphors are selected from the group consisting of (a) M<NUM>B<NUM>O<NUM>:Eu<NUM>+ and (b) A<NUM>B<NUM>O<NUM>:Ce<NUM>+, wherein M comprises one or more of Sr and Ca, wherein A comprises one or more of Y, Gd, and Lu, and wherein B comprises one or more of Al, Ga, In and Sc. In embodiments, the one or more phosphors only comprise M<NUM>B<NUM>O<NUM>:Eu<NUM>+ and/or A<NUM>B<NUM>O<NUM>:Ce<NUM>+.

In embodiments, the one or more phosphors comprise M<NUM>B<NUM>O<NUM>:Eu<NUM>+, wherein M comprises Sr and optionally Ca, and wherein B comprises Al and optionally Sc. In embodiments, M may comprise equal to or less than <NUM> % Ca, especially at maximum <NUM>%, such as at maximum <NUM>%. In embodiments, M may comprise <NUM>-<NUM>%, such as <NUM>-<NUM>%, like especially <NUM>-<NUM>% Eu. Hence, M may in embodiments essentially comprise Sr (and some Eu). Eu is especially a dopant. In embodiments, B may comprise equal to or less than <NUM>% Sc, such as especially at maximum <NUM>%, like at maximum <NUM>% Sc. In embodiments, B may comprise at least <NUM>%, such as at least <NUM>% Sc. Scandium may provide a useful blue shift of the emission. Hence, in embodiments B may essentially comprise Al. Here, percentages refer to atom percentages.

In embodiments, the one or more phosphors comprise A<NUM>B<NUM>O<NUM>:Ce<NUM>+, wherein A comprises one or more of Y and Lu, and wherein B comprises one or more of Al and Ga. In embodiments, A may comprise <NUM>-<NUM>% Ce, such as <NUM>-<NUM>% Ce. In embodiments, A may essentially consist of one or more of Y and Lu (and some Ce). In embodiments, A may essentially consist of Y and Ce (with e.g. <NUM>-<NUM>% Ce). Alternatively, in embodiments A may essentially consist of Lu and Ce (with e.g. <NUM>-<NUM>% Ce). Alternatively, in embodiments A may essentially consist of Lu and Y and Ce (with e.g. <NUM>-<NUM>% Ce). In embodiments, B may comprise Al and optionally Ga. B may comprise at least <NUM>%, such as at least <NUM>% Al. In embodiments, B may comprise at maximum <NUM>% Ga, such as at maximum <NUM>%. For instance, A<NUM>B<NUM>O<NUM>:Ce<NUM>+ may comprise one or more of Lu<NUM>(Al<NUM>,Ga<NUM>)O<NUM>:Ce, (Lu,Y)<NUM>Al<NUM>O<NUM>:Ce, and Y<NUM>Al<NUM>O<NUM>:Ce. Here, percentages refer to atom percentages.

In specific embodiments, the one or more phosphors comprise a A<NUM>B<NUM>O<NUM>:Ce<NUM>+ phosphor. In other specific embodiments, the one or more phosphors comprise only a A<NUM>B<NUM>O<NUM>:Ce<NUM>+ phosphor and no other phosphors.

In yet other specific embodiments the one or more phosphors comprise M<NUM>B<NUM>O<NUM>:Eu<NUM>+ and A<NUM>B<NUM>O<NUM>:Ce<NUM>+, wherein relative to a total weight of the two (types of) phosphors A<NUM>B<NUM>O<NUM>:Ce<NUM>+ is available in an amount of <NUM>-<NUM> wt%, such as <NUM>-<NUM> wt%. Hence, in specific embodiments the one or more phosphors comprise M<NUM>B<NUM>O<NUM>:Eu<NUM>+ and A<NUM>B<NUM>O<NUM>:Ce<NUM>+, wherein relative to a total weight of the phosphors, A<NUM>B<NUM>O<NUM>:Ce<NUM>+ is available in a weight percentage of <NUM>-<NUM> wt%. Adding garnet to the M<NUM>B<NUM>O<NUM>:Eu<NUM>+ phosphor appears to increase the flux but also surprisingly allows a lower loading in a resin, such as a silicone resin. In embodiments, the weight percentage of the one or more phosphors in a resin is less than <NUM> wt% (relative to the total weight of resin including the phosphors). Hence, in embodiments the one or more phosphors are comprised by a resin, wherein relative to a total weight of the resin and phosphors, the one or more phosphors are available in a weight percentage of less than <NUM> wt%. The resin may be a host for the phosphor(s). Here, the percentages refer to weight percentages.

The use of M<NUM>B<NUM>O<NUM>:Eu<NUM>+ appeared to surprisingly provide a LED with a color point that stays within the desired (narrow) cyan color box, even at operating temperatures, and also over a long period of operation time.

In embodiments, the LED has a peak wavelength selected from the range of <NUM>-<NUM>.

Schematic drawings, if any, may not necessarily be to scale.

The following detailed description should be read with reference to the drawings, in which identical reference numbers refer to like elements throughout the different figures. The drawings, which are not necessarily to scale, depict selective embodiments and are not intended to limit the scope of the invention.

This specification discloses pcLEDs having color-stable emission within a defined portion of the cyan range of the CIE <NUM> color space. These pcLEDs may have applications as signaling lights in the automobile industry, as well as other uses.

Colors for signaling and illumination in the automobile industry are defined in a CIE color space, for example in the CIE <NUM> color space. Between the color space definitions for blue and green signaling in the automobile industry, a small region is free and currently proposed for use for signaling the autonomous driving states of automobiles. In CIE <NUM> color space coordinates, this cyan range is <NUM> ≤ y ≤ <NUM> and x ≤ <NUM>. <FIG> shows this cyan region <NUM> plotted in a CIE <NUM> x,y chromaticity diagram, along with a portion of the monochromatic locus <NUM> and selected wavelengths of light along the monochromatic locus.

It is challenging to manufacture and operate LEDs having direct emission within cyan region <NUM>. As shown in <FIG>, the dominant wavelengths (extending along the monochromatic locus <NUM>) for cyan region <NUM> range only from about <NUM> nanometers (nm) to about <NUM>. In production of cyan emitting AlInGaN LEDs, for example, typically the range of dominant wavelengths emitted by individual devices manufactured on a single wafer is a multiple of this range. Further, the dominant wavelength shift of an AlInGaN LED with driving current is about -<NUM> per Ampere, and with temperature about <NUM> per <NUM> of temperature change. Consequently, it is difficult to achieve sufficient color stability during operation of a direct cyan emitting LED to stay within cyan region <NUM> over the likely range of operating temperature and drive current conditions.

The inventors have determined that a pcLED comprising a light emitting diode or laser diode and one or more phosphor materials can provide stable emission in cyan region <NUM>. The peak emission wavelength of the LED may range from deep ultraviolet up to about <NUM> in wavelength. The one or more phosphor materials may convert only a fraction of the light emitted by the LED to light of longer wavelengths, or convert essentially all of the light emitted by the LED to light of longer wavelengths. That is, the light emitted by the pcLED may comprise a mixture of light emitted by the LED and light emitted by the one or more phosphor materials resulting in an emission spectrum from the pcLED with color point inside cyan region <NUM> defined above. Alternatively, the light emitted by the pcLED may include only light emitted by the one or more phosphors, resulting in an emission spectrum from the pcLED with color point inside cyan region <NUM>.

The emission spectrum from the one or more phosphor materials typically has a defined peak wavelength with a full width at half maximum (FWHM). <FIG> shows a <NUM> CIE x,y chromaticity diagram as in <FIG>, on which are plotted the color points of phosphor emission spectra for different locations of peak wavelength and FWHM. The color points indicated by an "x" symbol are for phosphor emission spectra peaking at the labeled wavelength, with FWHM of <NUM>. The color points indicated by a solid square are for phosphor emission spectra peaking at the labeled wavelength, with FWHM of <NUM>. The light emission of the phosphor material may come from one material, or a mixture of different phosphor materials, which in total result in FWHM and peak position as indicated in <FIG>.

As demonstrated by <FIG>, only some combinations of phosphor emission spectrum peak wavelength and FWHM result in color points that fall within cyan region <NUM>. For those cases in which the color point of the phosphor emission spectrum falls within cyan region <NUM>, the pcLED may be configured so that little or none of the light emitted by the LED is present in the light emission from the pcLED. Alternatively, in some cases in which the color point of the phosphor emission spectrum falls outside of region <NUM> because the peak wavelength of the phosphor emission spectrum is long, the pcLED may be configured so that some unabsorbed blue light emitted by the LED is mixed with the phosphor emission to shift the color point of the pcLED emission spectrum into region <NUM>.

<FIG> shows two example phosphor emission spectra from color points shown in <FIG>. Phosphor emission spectrum <NUM> (full line) has a peak wavelength of <NUM> and a FWHM of <NUM>. Phosphor emission spectrum <NUM> (dashed line) has a peak wavelength of <NUM> and a FWHM of <NUM>.

From data similar to that shown in <FIG> the inventors have determined that a pcLED having an emission spectrum with a color point falling within cyan region <NUM> may be constructed using one or more phosphors providing a total phosphor emission spectrum having a peak wavelength λpk and a FWHM satisfying the following inequalities, with λpk and FWHM expressed in nm: <MAT>.

For longer λpk cyan color region <NUM> can be realised with addition of blue light from the LED. However, for λpk above about <NUM> the y-coordinate of the phosphor emission rapidly decreases. The amount of blue light from the LED mixed into the pcLED output can be characterized by the ratio PR of the power of blue LED light emission in the output to the power of phosphor light emission in the output: PR= (blue power) / (phosphor power). Typically, <NUM> ≤ PR ≤ <NUM>, or <NUM> ≤ PR ≤ <NUM>. Preferably, <NUM> ≤ PR ≤<NUM>. More preferably, <NUM> ≤ PR ≤ <NUM>. For λpk = <NUM> and FWHM = <NUM>, PR = <NUM>. For λpk = <NUM> and FWHM = <NUM>, PR = <NUM>. For λpk = <NUM> and FWHM = <NUM>, PR = <NUM>.

In phosphor-converted LEDs providing an emission spectrum with a color point in cyan region <NUM>, the light emitting diode or laser diode may be, for example, a conventional AlInGaN light emitting diode or laser diode. Any other suitable light emitting diode or laser diode may be used instead. The phosphor may be or comprise a Sr<NUM>Al<NUM>O<NUM>:Eu<NUM>+ (SAE) phosphor, for example, which is a known material used in fluorescent lighting applications. In general flux can be increased by addition to the SAE phosphor of a garnet phosphor of the general formula (Y,Lu)<NUM>(Al,Ga)<NUM>O<NUM>:Ce, a garnet material with a preferably greener emission than a standard YAG material. An example of such a garnet phosphor is GaLuAG activated with Cerium. Other suitable phosphors that may be combined with SAE include β-SiSlON:Eu<NUM>+, BOSE (Eu doped Sr,Ba orthosilicate), and nitride green phosphors such as or similar to Ba<NUM>,Si<NUM>,O<NUM>:Eu. Any other suitable phosphor may be used in addition or instead.

An example pcLED providing the desired cyan output was constructed using a conventional mid-power AlInGaN LED package with a Sr<NUM>Al<NUM>O<NUM>:Eu<NUM>+ phosphor dispersed in silicone. The phosphor silicone mixture was made with <NUM> mass% of the silicone, that is, the mass of the phosphor was <NUM> times the mass of the silicone.

The AlInGaN LED emission spectrum peaked at <NUM> with a FWHM of <NUM>. This is a very long blue wavelength with little overlap with the absorption band of SAE. At room temperature, the phosphor emission spectrum had a peak wavelength of <NUM> with a FWHM of <NUM>. <FIG> shows the AlInGaN LED emission spectrum <NUM> and the resulting pcLED cyan emission spectrum <NUM> with the SAE phosphor and silicone mixture in the package. Some blue light emitted by the LED is present in the pcLED output. The power ratio PR in this example is about <NUM>.

<FIG> shows a <NUM> CIE x,y chromaticity diagram similar to that of <FIG>, on which are plotted the color points of the example cyan pcLED of <FIG> as a function of operating temperature and drive current. The color points were determined from measured pcLED emission spectra for socket temperatures of <NUM>, <NUM> and <NUM>, and at drive currents of <NUM> mA, 10mA, 50mA, 100mA, 150mA, 200mA and 350mA. This data demonstrates that over this range of temperature and driving conditions the cyan emission of the example pcLED is always well with the defined cyan color region <NUM>.

Another example pcLED providing the desired cyan output was constructed using a conventional mid-power AlInGaN LED package with a mixture of Sr<NUM>Al<NUM>O<NUM>:Eu<NUM>+ phosphor and a green emitting Cerium activated GaLuAG phosphor dispersed in silicone. The SAE phosphor component of the silicone mixture was <NUM> mass% of the silicone, and the GaLuAG phosphor component was <NUM> mass% of the silicone. The AlInGaN LED emission spectrum peaked at <NUM> with a FWHM of <NUM>.

<FIG> shows the AlInGaN LED emission spectrum <NUM> and the resulting pcLED cyan emission spectrum <NUM>, as well as the SAE phosphor emission contribution <NUM> to the cyan emission, the LED blue light contribution <NUM> to the cyan emission, and the GaLuAG phosphor emission contribution <NUM> to the cyan emission. The different contributions in optical power fraction to the pcLED output are: SAE = <NUM>%, GaLuAG = <NUM>%, and LED = <NUM>%. The power ratio is PR = <NUM>. This pcLED has a luminous equivalent (LE) of <NUM> lm/W, CIE <NUM> color space coordinates x = <NUM> and y = <NUM>, and a luminous flux of <NUM> lumens at <NUM> mA drive current. In contrast, a similar pcLED built with a blue LED having the same peak emission wavelength and FWHM but using only SAE phosphor has a LE of <NUM> lm/W, CIE <NUM> color space coordinates x = <NUM> and y = <NUM>, a luminous flux of <NUM> lumens at <NUM> mA drive current, and a PR of <NUM>. These examples show that adding the GaLuAG phosphor advantageously increases the x coordinate of the pcLED output and provides a luminous flux gain of about <NUM>%. Here, λpk = <NUM>, and the FWHM is <NUM>.

Another example pcLED providing the desired cyan output was constructed using a conventional mid-power AlInGaN LED package with a mixture of Sr<NUM>Al<NUM>O<NUM>:Eu<NUM>+ phosphor and a yellow-green emitting Cerium activated YAG phosphor dispersed in silicone. The SAE phosphor component of the silicone mixture was <NUM> mass% of the silicone, and the YAG phosphor component was <NUM> mass% of the silicone. The AlInGaN LED emission spectrum peaked at <NUM>.

<FIG> shows the AlInGaN LED emission spectrum <NUM> and the resulting pcLED cyan emission spectrum <NUM>, as well as the SAE phosphor emission contribution <NUM> to the cyan emission, the LED blue light contribution <NUM> to the cyan emission, and the YAG phosphor emission contribution <NUM> to the cyan emission. The different contributions in optical power fraction to the pcLED output are: SAE = <NUM>%, YAG = <NUM>%, and LED = <NUM>%. The power ratio is PR = <NUM>. This pcLED has a luminous equivalent (LE) of <NUM> lm/W, CIE <NUM> color space coordinates x = <NUM> and y = <NUM>, and a luminous flux of <NUM> lumens at <NUM> mA drive current. This example shows that also adding the YAG phosphor advantageously increases the x coordinate of the pcLED output and provides a luminous flux gain of about <NUM>%. Here, λpk = <NUM> and the FWHM is <NUM>.

In the pcLEDs, the one or more phosphor materials may be arranged with respect to the LED in any suitable manner. Referring to <FIG>, for example, a pcLED <NUM> may comprise an LED <NUM> disposed in a reflective structure (e.g., a reflective cup) <NUM>, which also contains a substantially transparent material <NUM> in which are dispersed phosphor particles <NUM>. Material <NUM> and phosphor particles <NUM> are disposed around LED <NUM>. During operation of pcLED <NUM>, at least a portion of the blue or ultraviolet light emitted by LED <NUM> excites phosphor particles <NUM> which in response emit longer wavelength light. Reflective cup <NUM> reflects some unabsorbed light from the LED back to phosphor particles <NUM> and thus enhances the conversion of light from the LED to phosphor emission. Reflective cup <NUM> also directs the light emitted by the phosphor particles, and optionally some unabsorbed light emitted by LED <NUM>, away from LED <NUM> to form an optical output of pcLED <NUM>. Optionally, more than one LED <NUM> may be disposed in reflective structure <NUM>. Transparent material <NUM> may be or comprise a silicone, for example. Any other suitable transparent material may be used instead.

In the example of <FIG>, a pcLED <NUM> comprises an LED <NUM> on which has been deposited a phosphor layer comprising phosphor particles <NUM> dispersed in a substantially transparent material <NUM>. The phosphor layer may be deposited by screen printing or stenciling, for example. LED <NUM> is disposed in a reflective structure <NUM> similarly to the example of <FIG>. Optionally, more than one LED <NUM> may be disposed in reflective structure <NUM>.

The one or more phosphor materials may optionally be disposed in a separate wavelength converting structure formed separately from the LED and then arranged with respect to the LED. Such a wavelength converting structure may be formed, for example, as a luminescent ceramic slab or as a sheet of transparent material in which phosphor particles are dispersed. The wavelength converting structure may, for example, be bonded directly to the LED, bonded to the LED by an adhesive layer, or spaced apart from the LED.

In the example of <FIG>, a wavelength converting structure <NUM> is disposed directly on and bonded to an LED <NUM>. In the example of <FIG>, a wavelength converting structure <NUM> is disposed in close proximity to LED <NUM> but not directly connected to LED <NUM>. For example, the wavelength converting structure <NUM> may be separated from the LED by an adhesive layer <NUM>, a small air gap, or any other suitable structure. The spacing between the LED and the wavelength converting structure may be, for example, less than <NUM>. In the example of <FIG>, a wavelength converting structure <NUM> is spaced apart from LED <NUM>. The spacing between the LED and the wavelength converting structure may be, for example, on the order of millimeters. Such a device may be referred to as a "remote phosphor" device. Remote phosphor arrangements may be used, for example, in backlights for displays.

Claim 1:
A light emitting device comprising:
an LED (<NUM>) emitting ultraviolet or blue light; and
one or more phosphors (<NUM>) excited by the ultraviolet or blue light and in response emitting longer wavelength light to provide a combined phosphor emission spectrum having an emission peak at wavelength λpk with a full width at half maximum of FWHM,
the wavelength λpk satisfying <NUM> ≥ λpk ≥ <NUM> * FWHM + <NUM> with λpk and FWHM expressed in nm, and the combined phosphor emission spectrum having an x,y color point in the <NUM> CIE color space that does not satisfy x < <NUM> and <NUM> < y < <NUM>;
optical output from the light emitting device, formed from at least the light emitted by the one or more phosphors and including blue light emitted by the LED, having an x,y color point with x < <NUM> and <NUM> < y < <NUM> in the <NUM> CIE color space;
the blue light from the LED shifting the x,y color point of the optical output of the light emitting device from that of the combined phosphor emission spectrum to the color point for which x < <NUM> and <NUM> < y < <NUM>;
and
the one or more phosphors being selected from the group consisting of (a) M<NUM>B<NUM>O<NUM>:Eu<NUM>+ + (b) A<NUM>B<NUM>O<NUM>:Ce<NUM>+, wherein M comprises one or more of Sr and Ca, wherein A comprises one or more of Y, Gd, and Lu, and wherein B comprises one or more of Al, Ga, In and Sc.