Patent number 8524118 is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "The present disclosure relates to a nitride phosphor, a method of preparing the same, and a white light-emitting device using the same, and more particularly, to a nitride phosphor having a wide full width at half maximum ('FWHM').
"An optical system may include a fluorescent lamp and an incandescent lamp. Fluorescent lamps, however, cause environmental problems due to mercury (Hg) included therein. Also, such optical systems have very short lifetimes and low efficiencies and thus are unsuitable for saving energy. Therefore, much research is being performed to develop more efficient white light-emitting devices.
"Such white light-emitting devices may produce white light by using at least one of the four following methods. Red, green and blue phosphors may be excited by an ultraviolet ('UV') light emitting diode ('LED') to produce white light, blue and green phosphors may be excited by a UV LED to produce white light, red and green phosphors may be excited by a blue LED to produce white light, or a yellow phosphor may be excited by a blue LED to produce white light.
"A commercially available green phosphor for a UV LED has an emission peak at about 535 nanometers (nm) and a full width at half maximum (`FWHM') of about 80 nm. If the green phosphor is used with a blue phosphor having an emission peak at about 450 nm and a FWHM of about 50 nm to form a white light, a light emission valley may occur near from about 470 to about 510 nm. Accordingly, color rendering of the white light may be undesirable.
"In a white light-emitting device using a UV LED as a light source, reabsorption of blue phosphor emission by a green phosphor and reabsorption of blue and green phosphor emission by a red phosphor deteriorate the overall efficiency of the white light-emitting device. Accordingly, in order to develop a phosphor for an LED, it is desirable that the phosphor have insubstantial or no reabsorption.
"When a white light is provided by exciting a single white phosphor using a UV LED as a light source, color rendering of the white light may be desirable because a light emission valley near 480 nm is reduced compared to when a blue LED and a yellow phosphor are used, or when a blue LED and a green phosphor are used. In addition, reabsorption that occurs when using two or three phosphors is avoided. Also, even when the single white phosphor is used with another phosphor, the single white phosphor has a wide FWHM, and thus excellent color rendering is obtained compared to when the single white phosphor is not used.
"Commercially available methods of preparing a nitride phosphor require process conditions which include a high temperature and high nitrogen gas pressure, e.g., more than 0.1 megaPascals (MPa). Thus, a special apparatus designed to withstand high temperature and high pressure is used. Moreover, unstable materials are used as starting materials, and thus, more stringent of conditions are desirably used to handle the starting materials. Accordingly, there remains a need for an improved nitride phosphor that is more easily synthesized."
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