Patent Publication Number: US-2013240849-A1

Title: Organic electroluminescent apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 101109336, filed on Mar. 19, 2012. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     TECHNICAL FIELD 
     The disclosure relates to a luminescent apparatus, more particularly to an organic electroluminescent apparatus. 
     BACKGROUND 
     An organic electroluminescent apparatus is an emissive display apparatus. Since an organic electroluminescent apparatus possesses the characteristics of wide viewing angle, high response speed (approximately 100 times faster than that of liquid crystals), light weight, adaptability to miniature and low-profile design of the corresponding hardware equipment, high light emitting efficiency, high color rendering index and plane light source, it has a great potential to become the new flat display panel of the next generation. 
     The current products mostly apply the tandem device structure to increase the efficiency and lifetime of an organic electroluminescent device. The tandem device structure relies on a connecting layer to connect two or more luminescent devices to achieve the summation of lifetimes and efficiencies. In application, a fluorescent material is mostly used in a blue light device as the blue luminescent material. Currently, the external quantum efficiency of a blue light device may reach 5%. Moreover, a higher efficiency phosphorous material is mostly used in a red light device and a green light device. Currently, the external quantum efficiency of a red light device and a green light device may reach 16%. After stacking the blue light device, the red light device and the green light device, an organic electroluminescent device having a white light frequency spectrum with high color rendering index and high color temperature is attained. 
     However, the white light temperature (approximately 5000K) emitted by the above-mentioned organic electroluminescent device tends to be high. If a low-temperature, white light organic electroluminescent device is to be fabricated, the efficiency of the blue light device has to be lower or the efficiency of the red light device and the green light device has to be increased. However the efficiency of the red light and green light device (16%) is already approaching the theoretical limit (about 20%). Accordingly, further increasing the efficiency of the red and green light is difficult. The current approach for realizing the low temperature white light is to apply an optical structure to lower the blue light efficiency. However, according to the above approach, a portion of the light emitting efficiency of the blue light device is lost. Ultimately, the efficiency of the overall organic electroluminescent apparatus is lower. 
     SUMMARY 
     An exemplary embodiment of the disclosure provides an organic electroluminescent apparatus, wherein the efficiency problem of the conventional tandem light emitting device and the color adjustment problem may be resolved. 
     An exemplary embodiment of the disclosure provides an organic electroluminescent apparatus. The above-mentioned organic electroluminescent apparatus includes a substrate, a first electrode layer, a first color luminescent layer, a second color luminescent layer, a second electrode layer and a first fluorescent layer. The substrate is configured at a first light emitting side of the organic electroluminescent apparatus. The first electrode layer is configured above the substrate. The first color luminescent layer is configured above the first electrode layer. The second color luminescent layer is configured above the first color luminescent layer. The third color luminescent layer is configured above the second color luminescent layer. A first color light emitted from the first color luminescent layer, a second color light emitted from the second color luminescent layer and a third color light emitted from the third color luminescent layer are mixed so as to form a white light. The second electrode layer is positioned on the third color luminescent layer. The first fluorescent layer is configured on the substrate. The first color light emitted from the first color luminescent layer excites the first fluorescent layer to emit the second color light, the third color light or a fourth color light. 
     An exemplary embodiment of the disclosure provides an organic electroluminescent apparatus. The above-mentioned organic electroluminescent apparatus includes a substrate, a first electrode layer, a first color luminescent layer, a second color luminescent layer, a third color luminescent layer, a second electrode layer and a fluorescent layer. The first electrode layer is configured above the substrate. The first color luminescent layer is configured above the first electrode layer. The second color luminescent layer is configured above the first color luminescent layer. The third color luminescent layer is configured above the second color luminescent layer. A first color light emitted from the first color luminescent layer, a second color light emitted from the second color luminescent layer and a third color light emitted from the third color luminescent layer are mixed to form a white light. The second electrode layer is positioned on the third color luminescent layer and is configured at one light emitting side of the organic electroluminescent apparatus. The fluorescent layer is configured on the second electrode layer, wherein the first color light emitted from the first color luminescent layer excites the fluorescent layer to emit the second color light, the third color light or a fourth color light. 
     According to the organic electroluminescent apparatus of the disclosure, the fluorescent layer is coated on the light emitting side of the organic electroluminescent apparatus. A portion of the first color light emitted from the first color luminescent layer can excite the fluorescent layer to emit the color light. Moreover, the color light emitted from the fluorescent layer using difference fluorescent materials mix with the first color light, the second color light and the third color light so as to form a white light having a lower color temperature. Hence, the adjustment of the color temperature of white light is achieved. Accordingly, the organic electroluminescent apparatus of the disclosure is provided with a fluorescent layer using different fluorescent materials that mix to form white lights of different color temperatures. The luminescent efficiency of the first color luminescent layer is effectively used. 
     The disclosure and certain merits provided by the application can be better understood by way of the following exemplary embodiments and the accompanying drawings, which are not to be construed as limiting the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic, cross-sectional view diagram of an organic electroluminescent apparatus according to a first exemplary embodiment of the disclosure. 
         FIG. 2  is a schematic, cross-sectional view diagram of an organic electroluminescent apparatus according to a second exemplary embodiment of the disclosure. 
         FIG. 3  is a schematic, cross-sectional view diagram of an organic electroluminescent apparatus according to a third exemplary embodiment of the disclosure. 
         FIG. 4  is a schematic, cross-sectional view diagram of an organic electroluminescent apparatus according to a fourth exemplary embodiment of the disclosure. 
         FIG. 5  is a schematic, cross-sectional view diagram of an organic electroluminescent apparatus according to a fifth exemplary embodiment of the disclosure. 
         FIG. 6  is a schematic, cross-sectional view diagram of an organic electroluminescent apparatus according to a sixth exemplary embodiment of the disclosure. 
         FIG. 7  is a schematic, cross-sectional view diagram of an organic electroluminescent apparatus according to a seventh exemplary embodiment of the disclosure. 
         FIG. 8  is a schematic, cross-sectional view diagram of an organic electroluminescent apparatus according to an eighth exemplary embodiment of the disclosure. 
         FIG. 9  is a schematic, cross-sectional view diagram of an organic electroluminescent apparatus according to a ninth exemplary embodiment of the disclosure. 
         FIG. 10  is a schematic, cross-sectional view diagram of an organic electroluminescent apparatus according to a tenth exemplary embodiment of the disclosure. 
         FIG. 11  is a schematic, cross-sectional view diagram of an organic electroluminescent apparatus according to an eleventh exemplary embodiment of the disclosure. 
         FIG. 12  is a schematic, cross-sectional view diagram of an organic electroluminescent apparatus according to a twelfth exemplary embodiment of the disclosure. 
         FIG. 13  is a schematic, cross-sectional view diagram of an organic electroluminescent apparatus according to a thirteenth exemplary embodiment of the disclosure. 
         FIG. 14  is a schematic, cross-sectional view diagram of an organic electroluminescent apparatus according to a fourteenth exemplary embodiment of the disclosure. 
         FIG. 15  is a diagram showing the relationships between the luminescent intensity and wave length of comparative example 1 and the exemplary embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS 
       FIG. 1  is a schematic cross-sectional view diagram of an organic electroluminescent apparatus according to a first exemplary embodiment of the disclosure. Referring to  FIG. 1 , the organic electroluminescent apparatus according to the first exemplary embodiment includes a substrate  102 , a first electrode layer  104 , a first color luminescent layer  110 , a second color luminescent layer  206 , a third color luminescent layer  208 , a second electrode layer  214  and a first fluorescent layer F 1 . 
     The substrate  102  is a transparent substrate, and the substrate  102  is constituted with a material that includes, for example, glass, organic polymer and other appropriate transparent materials. In this exemplary embodiment, the substrate  102  is configured at a first light emitting side of the organic electroluminescent apparatus  100   a.    
     The first electrode layer  104  is configured above the substrate  102 . According to an exemplary embodiment, the first electrode layer  104  is a transparent electrode layer, and first electrode layer  104  is constituted with a material that includes, for example, metal oxide, such as indium-tin oxide (ITO), indium-zinc oxide (IZO) gallium-zinc oxide (GZO), zinc-tin oxide (ZTO), or other metal oxide materials. 
     The first color luminescent layer  110  is configured above the first electrode  104 . The first color luminescent layer  110  emits a first color light. According to the exemplary embodiment, the first color luminescent layer  110  may be a blue color luminescent layer. Accordingly, the first color light is a blue light. The blue luminescent layer may be a blue fluorescent material or a blue phosphor material. In application, limited by the color of the light and the life time of the material, the first color luminescent layer  110  is constructed with a blue fluorescent material with a longer life time, and the external quantum efficiency of the blue fluorescent material is about 5%. 
     The second color luminescent layer  206  is configured above the first color luminescent layer  110 . The second color luminescent layer  206  emits a second color light. According to an exemplary embodiment, the second color luminescent layer  206  may be a red luminescent layer. Therefore, the second color light is a red light. The red luminescent layer may be a red fluorescent material or a blue phosphor material. In application, the second color luminescent layer  206  includes a red phosphor material having a higher efficiency. 
     The third color luminescent layer  208  is configured above the second color luminescent layer  206 . The third color luminescent layer  208  emits a third color light. According to the exemplary embodiment of the disclosure, the third color luminescent layer  208  may be a green luminescent layer. Therefore, the third color light is a green light. The green luminescent layer may be a green fluorescent material or a green phosphor material. In application, the third color luminescent layer  208  of this exemplary embodiment applies the green phosphor material having a higher efficiency. Moreover, the sum of the external quantum efficiencies of the second color luminescent layer  206  and the third color luminescent layer  208  is about 16%. 
     It is worthy to note that although the third color luminescent layer  208  in the exemplary embodiment is positioned above the second color luminescent layer  206 , the embodiment is presented by way of example and not by way of limitation. According to other exemplary embodiments, the second color luminescent layer  206  may be disposed on the third color luminescent layer  208  (alternatively speaking, the positions of the second color luminescent layer  206  and the third color luminescent layer  208  can be exchanged). 
     According to the above disclosure, the first color light emitted from the first color luminescent layer  110 , the second color light emitted from the second color luminescent layer  206 , and the third color light emitted from the third color luminescent layer  208  are mixed so as to form a white light. 
     The second electrode layer  214  is positioned above the third color luminescent layer  208 . According to the exemplary embodiment, the second electrode layer  214  includes a metal electrode material, such as aluminum, aluminum/lithium alloy, magnesium/silver alloy or other metal materials. 
     The first fluorescent layer F 1  is configured on an internal surface of the substrate  102 . According to this exemplary embodiment, the fluorescent material of the first fluorescent layer F 1  includes silicate, yttrium aluminum garnet (YAG, Y 3 Al 2 (AlO 4 ) 3 ), green fluorescent powders, red fluorescent powders, lutetium aluminum garnet (LuAG, Lu 3 Al 2 (AlO 4 ) 3 ), terbium aluminum garnet (TbAG, Tb 3 Al 2 (AlO 4 ) 3 ) or other appropriate fluorescent materials. The thickness of the first fluorescent layer F 1  is about 0.1 μm to 1 mm. The concentration of the fluorescent material in the first fluorescent layer F 1  is about 0.1% to 3%. 
     It should be noted that the first color light emitted from the first color luminescent layer  110  may excite the first fluorescent layer F 1  to emit the second color light, the third color light or a fourth color light. More specifically, the first fluorescent layer F 1 , after being excited by the first color light (blue light), may emit a red light, a green light or a mixed color light of the red light and the green light. It should also be noted that this embodiment is presented by way of example and not by way of limitation. The type of the fourth color light may be selected according to the color temperature of the white light of the organic electroluminescent apparatus. Alternatively speaking, one of ordinary skill in the art may determine the type of white light emitted from the excited first fluorescent layer based on the white light color temperature emitted from the first light emitting side. In one exemplary embodiment, after the first fluorescent layer is excited by the first color light (for example, a blue light), the first fluorescent layer emits both the red light and the green light. 
     Moreover, the color temperature of the white light formed by the mixing of the first color light, the second color light and the third color light is at about 5000K. When the above white light penetrates through the first fluorescent layer F 1 , the part of the first color light that constitutes the white light excites the first fluorescent layer F 1  to emit the second color light, the third color light or the fourth color light. Accordingly, the intensity of the first color light in the original white light correspondingly reduces, and the intensity of the second color light, third color light or the fourth color light correspondingly increases. Hence, the color temperature of the white light emitted from the first light emitting side can be adjusted. 
     It is worthy to notice that, in this exemplary embodiment, a portion of the first color light is transformed into the second color light, the third color light or the fourth color light to achieve the adjustment of the white light temperature. Since the adjustment of the white light temperature is not achieved via the suppression of the luminous intensity of the first color light (the blue light), the first color light (the blue light) can be completely used according to the method of this exemplary embodiment; hence, the light emitting efficiency of the organic electroluminescent apparatus of the exemplary embodiment of the disclosure is enhanced. Additionally, by altering one of the parameters of the type of the fluorescent material, the thickness and the concentration of the fluorescent material of the first fluorescent layer F 1 , the color temperature of the white light can be further adjusted. 
     In this exemplary embodiment, the organic electroluminescent apparatus  100   a  further includes a charge generation layer C. The charge generation layer C is positioned between the first color luminescent layer  110  and the second color luminescent layer  206 . The charge generation layer C is used to connect the luminescent unit foamed by the first color luminescent layer  110  and the luminescent units formed by the second color luminescent layer  206  and the third color luminescent layer  208 . 
     In order to enhance the electron-hole combination rate of the first color luminescent layer  110  for increasing the light emitting efficiency, a first hole injection layer  106  is typically configured between the first electrode layer  104  and the first color luminescent layer  110 ; a first hole transmission layer  108  is configured between the first hole injection layer  106  and the first color luminescent layer  110 ; and a first electron transmission layer  112  is configured between the charge generation layer C and the first color luminescent layer  110 . 
     Similarly, in order to enhance the electron-hole combination rate of the second color luminescent layer  206  and the third color luminescent layer  208  for increasing their light emitting efficiency, a second hole injection layer  202  is typically configured between the second color luminescent layer  206  and the charge generation layer C; a second hole transmission layer  204  is configured between the second hole injection layer  202  and the second color luminescent layer  206 ; a second electron transmission layer  210  is configured between the third color luminescent layer  208  and the second electrode layer  214  layer; and a second electron injection layer  212  is configured between the second electron transmission layer  210  and the second electrode layer  214 . 
     It is worthy to note that the invention is not limited to an organic electroluminescent device  100   a  being configured with the above-mentioned electron injection layer, electron transmission layer, hole injection layer and hole transmission layer. The invention is also not limited to an organic electroluminescent device  100   a  being configured with the number of layers of the above-mentioned electron injection layer, electron transmission layer, hole injection layer and hole transmission layer. In a practical application, the layer numbers of the electron injection layer, the electron transmission layer, the hole injection layer and the hole transmission layer are determined by the selected materials of the first electrode layer  104 , the first color luminescent layer  110 , the second color luminescent layer  206 , the third color luminescent layer  208 , the second electrode layer  214  and the charge generation layer C. 
     Moreover, the organic electroluminescent apparatus  100   a  further includes a top cap layer  216  covering the second electrode layer  214 . The top cap layer  216  serves to strengthen the organic electroluminescent apparatus  100   a.    
     Moreover, the organic electroluminescent apparatus  100   a  further includes a package cover panel  218 . The package cover panel  218  covers the second electrode  214 . Generally speaking, the package cover panel  218 , in combination with an encapsulant (not shown), encapsulates the organic electroluminescent apparatus  100   a . The package cover panel  218  strengthens the organic electroluminescent device  100   a  and provides a hermetic effect of preventing moisture and oxygen from entering into the organic electroluminescent device  100   a.    
     According to the first exemplary embodiment, the first fluorescent layer F 1  is disposed on the internal surface  102   a  of the substrate  102 , but the disclosure is not limited hereto.  FIG. 2  is a schematic cross-sectional view diagram of an organic electroluminescent apparatus according to a second exemplary embodiment of the disclosure. Referring to  FIG. 2 , the organic electroluminescent apparatus  100   b  of the second exemplary embodiment is similar to the organic electroluminescent apparatus  100   a  of the first exemplary embodiment, and the difference between these two organic electroluminescent apparatuses lies in that the first fluorescent layer F 1  of the organic electroluminescent apparatus  100   b  is disposed on an outer surface  102   b  of the substrate  102 . 
     Moreover, the organic electroluminescent device  100   a  of the first exemplary embodiment and the organic electroluminescent device  100   b  of the second exemplary embodiment are both the bottom-emission type organic electroluminescent apparatus. The invention, however, is not limited to the bottom-emission type organic electroluminescent apparatus. The double-side emission type organic electroluminescent apparatus will be discussed in details in following exemplary embodiments. 
     Wherever possible, the same reference numbers are used to refer to the same or like parts in the previous and the following exemplary embodiments. Similar technical details, which can be referred to the previous exemplary embodiments for reference, will be omitted and not be further discussed. 
       FIG. 3  is a schematic cross-sectional view diagram of an organic electroluminescent apparatus according to a third exemplary embodiment of the disclosure. Referring to  FIG. 3 , according to the third exemplary embodiment, the organic electroluminescent device  100   c  is a double-side emission type organic electroluminescent apparatus. The structures and the compositions of the organic electroluminescent apparatus  100   c  and the organic electroluminescent device  100   a  are similar. The major difference between the two devices lies in the organic electroluminescent device  100   c  further including a second fluorescent layer F 2 . The difference between the two devices is discussed hereinafter. 
     According to the third exemplary embodiment, the second electrode layer  214  is a transparent conductive layer, wherein the material of the second electrode layer  214  includes, but not limited to, metal oxide, such as indium-tin oxide (ITO), indium-zinc oxide (IZO), gallium-zinc oxide (GZO), zinc-tin oxide (ZTO) or a thin metal layer, etc. Since the organic electroluminescent device in this exemplary embodiment is a double-side emission type, the second electrode layer  214  is positioned at a second light emitting side of the organic electroluminescent device  100   c.    
     The second fluorescent layer F 2  is configured on the interior surface  214   a  of the second electrode layer  214 . The fluorescent material of the second fluorescent layer F 2  includes silicate, yttrium aluminum garnet (YAG, Y 3 Al 2 (AlO 4 ) 3 ), green fluorescent powders, red fluorescent powders, lutetium aluminum garnet (LuAG, Lu 3 Al 2 (AlO 4 ) 3 ), terbium aluminum garnet (TbAG, Tb 3 Al 2 (AlO 4 ) 3 ) or other appropriate fluorescent materials. The thickness of the second fluorescent layer F 2  is about 0.1 μm to 1 mm. The concentration of the fluorescent material in the first fluorescent layer F 1  is about 0.1% to 3%. Although in the organic electroluminescent apparatus, the second fluorescent layer F 2  and the first fluorescent layer F 1  are constituted with the same type of materials, the invention should not be construed as limited to the embodiments set forth herein. The first color light emitted from the first color luminescent layer  110  excites the second luminescent layer F 2  to emit the second color light, the third color light or the fourth color light. 
     Accordingly, in the organic electroluminescent device  100   c , the substrate  102  is positioned at the first light emitting side, and the second electrode layer  214  is positioned at the second light emitting side. The first fluorescent layer F 1  is configured on the internal surface  102   a  of the substrate  102 , the second fluorescent layer F 2  is configured on the internal surface  214   a  of the second electrode layer  214 . The first color light emitted from the first color luminescent layer  110  simultaneously excites the first fluorescent layer F 1  and the second fluorescent layer F 2  to emit different color lights. 
     Similar to the organic electroluminescent device  100   a , the first color light emitted from the first color luminescent layer  110 , the second color light emitted from the second color luminescent layer  206  and the third color light emitted from the third color luminescent layer  208  are mixed to form a white light. The organic electroluminescent apparatus  100   c  is a double-side emission type, and the first fluorescent layer F 1  may adjust the white light color temperature emitted from the first light emitting side of the organic electroluminescent apparatus  100   c . The second fluorescent layer F 2  may adjust the white light temperature emitted form the second light emitting side of the organic electroluminescent apparatus  100   c.    
     It is worthy to note that although in the organic electroluminescent apparatus  100   c  of the third exemplary embodiment, the first fluorescent layer F 1  is positioned on the internal surface  102   a  of the substrate  102 , the second fluorescent layer F 2  is configured on the internal surface  214   a  of the second electrode layer  214 , it is to be understood that these embodiment is presented by way of example and not by way of limitation. In the following disclosure, several exemplary embodiments are discussed. More particularly, the structures and the compositions of the organic electroluminescent apparatus  100   d  to  100   j  in the following exemplary embodiments as shown in  FIGS. 4  to  10  are similar to those of the organic electroluminescent apparatus  100   c . The differences between the apparatuses are discussed here-below. 
       FIG. 4  is a schematic cross-sectional view diagram of an organic electroluminescent apparatus according to a fourth exemplary embodiment of the disclosure. Referring to  FIG. 4 , in the organic electroluminescent device  100   d , the first fluorescent layer F 1  is configured on the internal surface  102   a  of the substrate  102 , and the second fluorescent layer F 2  is configured on the external surface  214   b  of the second electrode layer  214 . 
       FIG. 5  is a schematic cross-sectional view diagram of an organic electroluminescent apparatus according to a fifth exemplary embodiment of the disclosure. Referring to  FIG. 5 , in the organic electroluminescent device  100   e , the first fluorescent layer F 1  is configured on the external surface  102   b  of the substrate  102 , and the second fluorescent layer F 2  is configured on the internal surface  214   a  of the second electrode layer  214 . 
       FIG. 6  is a schematic cross-sectional view diagram of an organic electroluminescent apparatus according to a sixth exemplary embodiment of the disclosure. Referring to  FIG. 6 , in the organic electroluminescent device  100   f , the first fluorescent layer F 1  is configured on the external surface  102   b  of the substrate  102 , and the second fluorescent layer F 2  is configured on the external surface  214   b  of the second electrode layer  214 . 
     Moreover, the package cover panel  218  may also be configured at the light emitting side of the organic electroluminescent apparatus. Accordingly, the second fluorescent layer F 2  may also be configured on the surface of the package cover panel  218 , and several exemplary embodiments thereof are discussed in the following disclosure. 
       FIG. 7  is a schematic cross-sectional view diagram of an organic electroluminescent apparatus according to a seventh exemplary embodiment of the disclosure. Referring to  FIG. 7 , in the organic electroluminescent device  100   g , the first fluorescent layer F 1  is configured on the internal surface  102   a  of the substrate  102 , and the second fluorescent layer F 2  is configured on the internal surface  218   a  of the package cover panel  218 . 
       FIG. 8  is a schematic cross-sectional view diagram of an organic electroluminescent apparatus according to an eighth exemplary embodiment of the disclosure. Referring to  FIG. 8 , in the organic electroluminescent device  100   h , the first fluorescent layer F 1  is configured on the internal surface  102   a  of the substrate  102  and the second fluorescent layer F 2  is configured on the external surface  218   b  of the package cover panel  218 . 
       FIG. 9  is a schematic cross-sectional view diagram of an organic electroluminescent apparatus according to a ninth exemplary embodiment of the disclosure. Referring to  FIG. 9 , in the organic electroluminescent device  100   i , the first fluorescent layer F 1  is configured on the external surface  102   b  of the substrate  102  and the second fluorescent layer F 2  is configured on the internal surface  218   a  of the package cover panel  218 . 
       FIG. 10  is a schematic cross-sectional view diagram of an organic electroluminescent apparatus according to a tenth exemplary embodiment of the disclosure. Referring to  FIG. 10 , in the organic electroluminescent device  100   j , the first fluorescent layer F 1  is configured on the external surface  102   b  of the substrate  102  and the second fluorescent layer F 2  is configured on the external surface  218   b  of the package cover panel  218 . 
     Accordingly, the positions of the first fluorescent layer F 1  and the second fluorescent layer F 2  of the invention are not limited. As long as the first fluorescent layer F 1  and the second fluorescent layer F 2  are respectively configured on the light emitting sides of the organic electroluminescent apparatus, the variations of embodiments fall within the spirit and scope of the invention. 
     Moreover, in the following exemplary embodiments, the top emission type of organic electroluminescent apparatus is disclosed in details. It should be noted that wherever possible, the same reference numbers are used to refer to the same or like parts in the previous and the following exemplary embodiments. Similar technical details, which can be referred to the previous exemplary embodiment for reference, will also be omitted and not be further discussed. 
       FIG. 11  is a schematic cross-sectional view diagram of an organic electroluminescent apparatus according to an eleventh exemplary embodiment of the disclosure. Referring to  FIG. 11 , the organic electroluminescent apparatus  100 K in this exemplary embodiment is a top-emission type of organic electroluminescent apparatus, which includes a substrate  102 , a first electrode layer  104 , a first color luminescent layer  110 , a second color luminescent layer  206 , a third color luminescent layer  208 , a second electrode layer  214  and a fluorescent layer F. 
     According to this exemplary embodiment, the first electrode layer  104  is configured on the substrate  102 . The first color luminescent layer  110  is configured on the first electrode layer  104 . The second color luminescent layer  206  is configured on the first color luminescent layer  110 . The third color luminescent layer  208  is configured on the second color luminescent layer  206 . The first color light emitted from the first color luminescent layer  100 , the second color light emitted from the second color luminescent layer  206 , and the third color light emitted from the third color luminescent layer  208  are mixed to foam a white light. The second electrode layer  214  is configured on the third color luminescent layer  208 , wherein the second electrode layer  214  is configured at the light emitting side of the organic electroluminescent apparatus  100   k . The fluorescent layer F is configured on the second electrode layer  214 , wherein the first color light emitted from the first color luminescent layer  110  excites the fluorescent layer F to emit a second color light, a third color light, or a fourth color light. 
     More particularly, the structure and the light emitting theory of the organic electroluminescent device  100   k  and those of the organic electroluminescent device  100   c  of the third exemplary embodiment are similar, wherein the fluorescent layer F of the organic electroluminescent device  100   k  is substantially the same as that of the second fluorescent layer F 2  of the organic electroluminescent apparatus  100   c . Accordingly, the first color light can excite the fluorescent layer F to emit a color light for adjusting the color temperature of the white light. 
     Moreover, the difference between the organic electroluminescent apparatus  100   k  and the organic electroluminescent apparatus  100   c  lies in that the organic electroluminescent apparatus  100   k  does not include the first fluorescent layer F 1  in the organic electroluminescent apparatus  100   c . The organic electroluminescent apparatus  100   k  includes only one light emitting side. 
     In addition, the organic electroluminescent device  100   k  of this exemplary embodiment further includes a reflective electrode  114 . The reflective electrode  114  covers the first electrode layer  104 . The reflective electrode  114  is constituted with a material that includes a metal electrode material, such as aluminum, silver or other metal materials. According to this exemplary embodiment of the disclosure, the reflective electrode  114  reflects the first color light, the second color light, and the third color light to the light emitting side for enhancing the light emitting efficiency of the organic electroluminescent apparatus  100   k.    
     Further, in other non-illustrated exemplary embodiments, the reflective electrode  114  may be disposed under the first electrode layer  104  or a substrate having a reflective function is directly used to reflect the color light without the application of the reflective electrode  114 . Alternatively, the first electrode layer  104  and the reflective electrode  114  are constituted with the same material and provide the same reflective function; hence, an additional reflective electrode is not required. 
     It is worthy to notice that, although the fluorescent layer F is configured on the internal surface  214   a  of the second electrode layer  214  according to the present exemplary embodiment, the invention should not be construed as limited to the embodiment set forth herein. In the organic electroluminescent device  100   l  of the twelfth exemplary embodiment of the disclosure, the fluorescent layer F is configured on the external surface  214   b  of the second electrode layer  214 , as shown in  FIG. 12 . 
     Further, the position of the fluorescent layer F of the invention should not be construed as limited to the embodiments set forth herein. In the organic electroluminescent apparatus  100   m  of the thirteenth exemplary embodiment of the disclosure, the fluorescent layer F may be configured on the internal surface  218   a  of the package cover panel  218 , as shown in  FIG. 13 . In the organic electroluminescent apparatus  100   n  of the fourteenth exemplary embodiment of the disclosure, the fluorescent layer F is configured on the external surface  218   b  of the package cover panel  218 , as shown in  FIG. 14 . 
     EXAMPLE 
     The following examples and the comparative example are used to illustrate an organic electroluminescent apparatus of the disclosure having a more favorable light emitting efficiency. 
     In the organic electroluminescent apparatus of the example, a blue fluorescent material is used for the first color emitting layer, a red phosphor material is used for the second color emitting layer, a green phosphor material is used for the third color emitting layer, and the fluorescent layer is configured on an external surface of the substrate, as the structure shown in  FIG. 2 . The organic electroluminescent apparatus of comparative example 1 does not include a fluorescent layer shown in  FIG. 2 . The organic electroluminescent apparatus of comparative example 2 is further disposed with an optical structure in the apparatus shown in  FIG. 2 , but does not include the fluorescent layer shown in  FIG. 2 . The above optical structure may suppress the light emitting efficiency of the blue light luminescent layer. 
     The light emitted from the organic electroluminescent layer of comparative example 1 and that of the example are subjected to light spectrum analysis.  FIG. 15  is a diagram showing the relationships between the luminous intensity and wavelength of the organic electroluminescent apparatus of comparative example 1 and that of the example of the disclosure. Comparing to comparative example 1, in the light spectrum of the example as shown in  FIG. 15 , the intensity of the color light (blue light) at the wavelength between 430 nm to 490 nm is lower, while the intensity of the color light at the wavelength between 630 nm to 680 nm is higher. Accordingly, with the disposition of the fluorescent layer, the blue light is absorbed and other color lights are excited. Hence, the disposition of a fluorescent layer definitely achieves the adjustment of the color temperature of the white light emitted from organic electroluminescent apparatus. 
     Moreover, the external quantum efficiency (EQE) measurement is performed on the organic electroluminescent apparatuses in comparative example 1, comparative example 2, and the exemplary embodiment, and the results are summarized in Table 1. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 EQE (%) 
                 EQE (%) of the 
                 Total EQE (%) 
                   
               
               
                   
                 of the 
                 red luminescent 
                 of the organic 
               
               
                   
                 blue lumi- 
                 layer and 
                 electro- 
                 Color 
               
               
                   
                 nescent 
                 the blue lumi- 
                 luminescent 
                 Tempera- 
               
               
                   
                 layer 
                 nescent layer 
                 apparatus 
                 ture (K) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Comparative 
                 5 
                 16 
                 21 
                 5000 
               
               
                 Example 1 
               
               
                 Comparative 
                 2 
                 16 
                 18 
                 2800 
               
               
                 Example 2 
               
               
                 Example 
                 2 
                 16 + 
                 20.4 
                 2500~4000 
               
               
                   
                   
                 3*0.8 = 
               
               
                   
                   
                 18.4 
               
               
                   
               
            
           
         
       
     
     According to Table 1, comparing to comparative example 1, the external quantum efficiency of the first color luminescent layer in the example is reduced by 3%. Accordingly, the fluorescent layer in the example may absorb about 3% of the blue color light and transforms the blue color light emitted by the first color luminescent layer into at least one of the red color light and green color light, wherein the energy transformation efficiency ratio of the fluorescent layer is about 0.8. Hence, the total external quantum efficiency of the red luminescent layer and the green luminescent layer is 18.4%. The total external quantum efficiency of the organic electroluminescent apparatus of the example is 20.4% and the color temperature is between about 2500 to 4000K. 
     Comparing to the high color temperature (5000K) white light emitted from the organic electroluminescent apparatus of comparative example 1, the color temperature of the white light emitted by the organic electroluminescent apparatus of the example may be adjusted by the disposition of a fluorescent layer to attain a white light with a lower color temperature. Moreover, although the organic electroluminescent layer of comparative example 2 can emit a white light with low color temperature (2800K), the organic electroluminescent apparatus of the second exemplary embodiment is unable to totally use the light emitting efficiency of the blue luminescent layer. Hence, the external quantum efficiency of the organic electroluminescent apparatus of comparative example 2 is only 18%. The external quantum efficiency of the example is higher than that of comparative example 2. Alternatively speaking, not only the organic electroluminescent apparatus of the example can provide a white light with a lower color temperature, a more favorable light emitting efficiency is resulted. 
     According to the organic electroluminescent apparatus of the disclosure, a fluorescent layer is coated on the light emitting side of the organic electroluminescent apparatus. The fluorescent layer can absorb the first color emitted by the first color luminescent layer and transforms it into other colors. Hence, the first color efficiency is reduced while the efficiencies of other colors are enhanced so as to adjust the color temperature of the white light emitted from the organic electroluminescent apparatus. Moreover, the white light color temperature of the organic electroluminescent apparatus of the disclosure can be adjusted according to the type, the thickness and the concentration of the fluorescent material in the fluorescent layer. Further, through the effective application of the light emitting efficiency of the first color luminescent layer, the organic electroluminescent apparatus of the invention having a favorable luminescent efficiency is provided. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.