1. Technical Field
Devices and compositions consistent with the present invention relate to phosphors and, more particularly, to phosphors that are efficiently excited by ultraviolet light or short-wavelength visible light to emit light, and a light emitting device using the phosphor.
2. Description of the Related Art
Various light emitting devices have been known that are configured to obtain desired color light by combining light emitting elements and phosphors, which are excited by light emitted from the light emitting elements and generate light having a wavelength range different from the wavelength range of the light emitted from the light emitting elements.
Particularly, in recent years, a light emitting device, which is configured to obtain white light by combining a semiconductor light emitting element, such as a light-emitting diode (LED) or a laser diode (LD), and a phosphor, has attracted attention as a white light emitting device that has long life and low power consumption. The semiconductor light emitting element emits ultraviolet light or short-wavelength visible light, and the phosphor uses ultraviolet light or short-wavelength visible light as an excitation light source.
As a specific example of the white light emitting device, a light emitting device has been known in which an LED for emitting ultraviolet light or short-wavelength visible light is combined with a plurality of phosphors that is excited by the ultraviolet light or short-wavelength visible light and respectively emits color light, such as blue light or yellow light (see e.g., JP-A-2009-38348 and its counterpart U.S. Pat. Pub. No. US2009/0015138 A1)
However, the emission spectrum of the phosphor, which is used for the above-mentioned white light emitting device and emits yellow light, does not correspond to a luminosity curve, and the peak wavelength of the emission spectrum of the phosphor is shifted toward a long wavelength side as compared to a wavelength where luminosity becomes maximum. For this reason, the conversion efficiency of a single phosphor is good, but the white light emitting device has been needed to be improved in terms of luminous flux and light emission efficiency.
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