Light emitting film, luminescent device, method for manufacturing light emitting film and method for manufacturing luminescent device

#The present invention relates to a luminescent film and a light emitting apparatus, which can be applied to a light source for lighting, an LED display, a back light source, a signal light, an illuminated switch, various sensors, various indicators, and so on, and a method for production of the luminescent film and light emitting apparatus.

#A light emitting apparatus which radiates light with color different from the light of a light emitting element has been developed. The light emitting apparatus converts a part of the light of the light emitting element into a different wavelength by a phosphor, and mixes the light with converted wavelength and the light with non-converted wavelength of the light emitting element (for example, Japanese Laid-Open Publication Kokai No. 2002-198573). For example, a while LED light emitting apparatus, which has a blue light emitting diode (hereinafter, occasionally referred to as an “LED”) and a phosphor member coating thereon, has been in actual use. The blue light emitting diode employs an InGaN group material is used as a light emitting element. The phosphor member is composed of a transparent material, such as an epoxy resin, containing an Yttrium aluminum garnet (hereinafter, occasionally referred to as “YAG”) group phosphor represented by the formula (Y,Gd)3(Al,Ga)5O12. The luminescent color of the white LED light emitting apparatus is obtained based on the additive color mixture principle. After the blue light emitted from the LED enters into the phosphor member, it is repeatedly absorbed and scattered in its layer, and then is outwardly radiated. On the other hand, the blue light absorbed by the phosphor serves as an excitation source, and exhibits yellow fluorescence. Human eyes recognize the mixture of the yellow light from the phosphor and the blue light from the LED as white.

#The LED light emitting apparatus using such an LED is small, highly effective in terms of electric power consumption, and emits vivid color light. Since an LED is a semiconductor element, it is not prone to burn out. In addition, it has features, such as excellent initial drive characteristics, resistance to vibration or ON/OFF repeats. Since LEDs have these excellent characteristics, LED light emitting apparatuses are used as various kinds of light sources.

#FIG. 1 is a graph showing the proceeding of sol-gel reaction, and the variation of transmittance of luminescent film;

#FIG. 2 is a schematic view showing a light emitting apparatus according to a first embodiment of the present invention;

#FIG. 3 is a plan view schematically showing a light emitting apparatus according to a second embodiment of the present invention;

#The following description will describe embodiments according to the present invention with reference to the drawings. It should be appreciated, however, that the embodiments described below are illustrations of a luminescent film and a light emitting apparatus, and a method for producing of a luminescent film and a light emitting apparatus to give a concrete form to technical ideas of the invention, and a luminescent film and a light emitting apparatus, and a method for producing of a luminescent film and a light emitting apparatus of the invention are not specifically limited to description below. Furthermore, it should be appreciated that the members shown in claims attached hereto are not specifically limited to members in the embodiments. Additionally, the sizes and the arrangement relationships of the members in each of drawings are occasionally shown larger exaggeratingly for ease of explanation. In addition, each element composing the present invention may be configured as a single member which is composed of the same member as a plurality of elements to serve the purpose of the plurality of element.

#In this embodiment of the present invention, gel of hydroxide oxide is employed as a binder. FIG. 1 is a graph showing variation of transmittance of luminescent film and variation of light-outgoing efficiency due to the proceeding of sol-gel reaction from the sol state to an amorphous or polycrystal oxide through gel or a hydroxide oxide containing water of crystallization. In the case where gel is used as a binder, as the gel becomes closer to the polycrystal structure by the proceeding of sol-gel reaction as shown in FIG. 1, it is generally considered that the transmittance of the light emitting film is improved as shown A in the Figure. However, considerable energy is required to obtain a polycrystal by the sol-gel reaction. Considerable high temperature is required to separate a hydroxyl group or an organic group included in the structure of a gel state. Accordingly, the separation is not easy.

#The inventors of the present invention have diligently studied, and as a result found that light-outgoing efficiency could be obtained even in a gel state without improvement of the crystallinity in the case of particular metallic elements. Thus, we have developed the present invention. We have found the light-outgoing efficiency in a gel state is tend to be higher than the light-outgoing efficiency in the polycrystal state where the sol-gel reaction is proceeded, particularly, in the case where hydroxide oxides, the ionic charge number of which does not vary in the sol-gel reaction process, with stable oxidation state such as Al and Y elements are used, as shown by B in FIG. 1. For example, in an amorphous substance such as yttria, it is considered that one reason is dispersion of light. That is, in the crystallization process from a to b where a multi-layer is formed at the crystallization stage by high-temperature heating in terms of chemical structure, it is considered that multi-phase structure is formed. In the structure, microscopically, phase separation of a partially-crystallized part and a gel-state part occurs. Accordingly, microscopically, the phases are uniform, and light is scattered at the interface between the phases, thus, the whole transmittance reduces. It is considered that another reason is the crystal structure. That is, in the state from a to b, due to coexistence of the crystalline region and the amorphous region caused by formation of spherulite or the like, the densities and refractive indices in regions are different. Even if microscopically it is uniform, optically the multi-layer structure is formed, thus, the whole transmittance reduces. Accordingly, even when the luminescent film is formed in a gel state without achievement of polycrystal, it is possible to easily obtain luminescent film with high light-outgoing efficiency for a short time at low energy without proceeding of the sol-gel reaction.