In the case of converting light from an emitting medium to light containing a component having a longer wavelength light ray, there is generally used a color conversion layer (fluorescent medium layer) which absorbs light (for example, light in a blue range) from the fluorescent medium and emits fluorescence having a longer wavelength.
At this time, the color conversion cannot be effectively attained since the light from the emitting medium is not sufficiently absorbed by the color conversion layer and the fluorescence therefrom is hindered from being taken outside because of self-absorption of the fluorescent medium in the color conversion layer.
Incidentally, a structure wherein light-scattering particles are dispersed into a color conversion layer has been investigated. As a result, it is disclosed that the lifetime of a color conversion filter is improved (see, for example, Japanese Patent Application Laid-open No. 2002-216962).
However, more efficient color conversion cannot be attained only by dispersing light-scattering particles into a color converting layer.
A fluorescent material in a color conversion layer may interact with light-scattering particles to cause extinction of fluorescence, or the color conversion efficiency thereof may be lowered with the passage of time by light from an emitting medium.
Accordingly, it has been desired to make clear a physical range in which color conversion can be more efficiently attained and thus develop a color conversion layer which exhibits only a small deterioration with the passage of time.