Light emitting device

Abstract

An object of the present invention is to provide a light emitting device which emits light of deep yellowish color with high luminance. The light emitting device of the present invention comprises a light emitting element having a peak emission wavelength shorter than 490 nm, a fluorescent material for wavelength conversion which absorbs light from the light emitting element and emits light of a wavelength longer than that of the light from the light emitting element, and a filter which cuts off a part of a mixed light produced by mixing the light of the light emitting element and the light of the fluorescent material, wherein the light transmitted through the filter has a chromaticity coordinate on the chromaticity diagram according to CIE 1931 plotted in a region defined by a first point (x=0.450, y=0.450), a second point (x=0.250, y=0.650), a third point (x=0.350, y=0.750) and a fourth point (x=0.250, y=0.750) and in the region defined by a closed curve consisting of the monochromatic locus and the purple boundary.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically showing the light emitting device according to an embodiment.

FIG. 2 shows chromaticity diagram (CIE 1931) and the range of the chromaticity coordinates of the light emitted by the light emitting device according to the embodiment.

FIG. 3 is a graph showing the transmittance of filter used in Examples 1 to 29.

FIG. 4 is an emission spectrum of (Y, Gd)₃Al₅O₁₂:Ce fluorescent material excited with light having wavelength of 450 nm.

FIGS. 5A and 5B are emission spectra of the light emitting device according to Examples 1 to 7, the emission spectra being measured on the mixed light yet to pass the filter. The fluorescent material was excited by the light emitted by the light emitting element.

FIG. 6 shows the chromaticity diagram (CIE 1931) in which chromaticity coordinates of the light emitted by the light emitting device according to Examples 1 to 7 are plotted, the color being measured on light emitted by the fluorescent material that was excited by the light emitted by the light emitting element and yet to pass the filter.

FIG. 7 shows the chromaticity diagram (CIE 1931) in which chromaticity coordinates of the light emitted by the light emitting device according to Examples 1 to 7 and passed the filter are plotted.

FIG. 8 is an emission spectrum of Y₃(Al, Ga)₅O₁₂:Ce fluorescent material excited with light having wavelength of 450 nm.

FIGS. 9A and 9B are emission spectra of the light emitting device according to Examples 8 to 12, the emission spectra being measured on the mixed light yet to pass the filter. The fluorescent material was excited by the light emitted by the light emitting element.

FIG. 10 shows the chromaticity diagram (CIE 1931) in which chromaticity coordinates of the light emitted by the light emitting device according to Examples 8 to 12 are plotted, the color being measured on light emitted by the fluorescent material that was excited by the light emitted by the light emitting element and yet to pass the filter.

FIG. 11 shows the chromaticity diagram (CIE 1931) in which chromaticity coordinates of the light emitted by the light emitting device according to Examples 8 to 12 and passed the filter are plotted.

FIG. 12 is an emission spectrum of Sr₅Si₃O₁₁:Eu fluorescent material excited with light having wavelength of 450 nm.

FIGS. 13A to 13C are emission spectra of the light emitting device according to Examples 13 to 22, the emission spectra being measured on the mixed light yet to pass the filter. The fluorescent material was excited by the light emitted by the light emitting element.

FIG. 14 shows the chromaticity diagram (CIE 1931) in which chromaticity coordinates of the light emitted by the light emitting device according to Examples 13 to 22 are plotted, the color being measured on light emitted by the fluorescent material that was excited by the light emitted by the light emitting element and yet to pass the filter.

FIG. 15 shows the chromaticity diagram (CIE 1931) in which chromaticity coordinates of the light emitted by the light emitting device according to Examples 13 to 22 and passed the filter are plotted.

FIG. 16 is an emission spectrum of SrGa₂S₄:Eu fluorescent material excited with light having wavelength of 450 nm.

FIGS. 17A and 17B are emission spectra of the light emitting device according to Examples 23 to 29, the emission spectra being measured on the mixed light yet to pass the filter. The fluorescent material was excited by the light emitted by the light emitting element.

FIG. 18 shows the chromaticity diagram (CIE 1931) in which chromaticity coordinates of the light emitted by the light emitting device according to Examples 23 to 29 are plotted, the color being measured on light emitted by the fluorescent material that was excited by the light emitted by the light emitting element and yet to pass the filter.

FIG. 19 shows the chromaticity diagram (CIE 1931) in which chromaticity coordinates of the light emitted by the light emitting device according to Examples 23 to 29 and passed the filter are plotted.

Claims

1. A light emitting device comprising: a light emitting element having a peak emission wavelength shorter than 490 nm;a fluorescent material for wavelength conversion which absorbs light emitted by said light emitting element and emits light of a wavelength longer than that of the light from said light emitting element; anda filter which cuts off a part of a mixed light produced by mixing the light from said light emitting element and the light from said fluorescent material, whereinthe light transmitted through the filter has of chromaticity coordinate on the chromaticity diagram according to CIE 1931plotted in a region defined by a first point (x=0.450, y=0.450), a second point (x=0.250, y=0.650), a third point (x=0.250, y=0.750) and a fourth point (x=0.550, y=0.450) and in a region defined by a closed curve consisting of the monochromatic locus and the purple boundary.

2. The light emitting device according to claim 1, wherein said filter transmits light of wavelengths shorter than 480 nm at a rate of about 10% or less when a maximum transmittance to light of wavelengths ranging from 380 nm to 730 nm is assumed to be 100%.

3. The light emitting device according to claim 1, wherein the mixed light before passing said filter has the ratio of an intensity of a peak emission wavelength of said fluorescent material to an intensity of peak emission wavelength of said light emitting element is about 1.0 or higher and not higher than about 20.

4. The light emitting device according to claim 1, wherein the mixed light before passing said filter consists of a light component having a peak emission wavelength of said light emitting element and a light component having a peak emission wavelength of said fluorescent material, and has a y value of a chromaticity coordinate on the chromaticity diagram according to CIE 1931not lower than about 0.400.