Patent Publication Number: US-2012043555-A1

Title: Liquid fluorescent composition and light emitting device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of China Patent Application No. 200910136313.9, filed on May 7, 2009, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a fluorescent agent, and more particularly to a fluorescent agent and applications thereof. 
     2. Description of the Related Art 
     In general, white light emitting diodes (LEDs) can be formed by using a blue light from a blue LED die to excite the YAG: Ce 3+  fluorescent powder to luminesce a yellow light and then the yellow light is mixed with the unabsorbed blue light to form a white light. Additionally, white light emitting diodes (LEDs) can be formed by using a light from a UV LED die to excite the red, green and blue (RGB) fluorescent powders and then mix the red, green and blue lights produced from the fluorescent powders to form a white light. 
     For the conventional fabrication method of white light emitting diodes, the fluorescent powders need to be mixed with a high transparent, high temperature resistant bonding agent, and then the mixture is cured to complete the LED. However, the fluorescent powder is incompatible with the bonding agent such that it does not disperse uniformly in the bonding agent and results in non-uniform luminescence from the LED. 
     Prior art patents relating to the field of fluorescent agents includes Taiwan Patent No. 459403, Taiwan Patent No. 565956, U.S. Pub. No. 20040231554, and JP 2004-326910. The patents, however, disclosed solid fluorescent compositions in which mixing is needed with a non-saturated transparent resin and a bonding or an accelerant and then curing to form a solid fluorescent layer for LEDs. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention provides a liquid fluorescent composition, including: 
     (a) 0.001-2 parts by weight of a fluorescent material, wherein the fluorescent material includes a fluorescent polymer, a fluorescent dye, or combinations thereof; and 
     (b) 100 parts by weight of a cyclic solvent having a boiling point above 100° C. 
     Further, the liquid fluorescent composition can optionally include: 
     (c) 1-50 parts by weight of a color modifying agent, or preferably 3-40 parts by weight; and 
     (d) 0.02-5 parts by weight of a hindered amine light stabilizer (HALS), or preferably 0.5-2 parts by weight. 
     The invention further provides a light emitting device, including: a substrate; a light emitting element disposed on the substrate; the aforementioned liquid fluorescent composition disposed on the light emitting element; and a sealing element encapsulating the liquid fluorescent composition into a chamber. 
     It should be noted that the liquid fluorescent composition absorbs a light with a first wavelength emitted by the light-emitting element and converts the light with the first wavelength to a light with a second wavelength. Further, the light with a first wavelength and the light with a second wavelength are mixed to serve as a white light source. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with reference to the accompanying drawings, wherein: 
         FIG. 1  shows a schematic cross section of a light emitting device according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. The description is provided for illustrating the general principles of the invention and is not meant to be limiting. The scope of the invention is best determined by reference to the appended claims. 
     The invention provides a liquid fluorescent composition and associated applications for use. The liquid fluorescent composition is different from a solid fluorescent composition prepared by curing the mixture of a fluorescent agent and a bonding resin. 
     In the present invention, dissoluble fluorescent materials are dissolved into a cyclic solvent, obtaining a homogeneous liquid fluorescent composition. The excitation wavelength of the liquid fluorescent composition can be adjusted by the conjugated degree of the cyclic solvent for achieving optimally luminescent performance thereof. 
     Further, an optional color modifying agent can be added into the liquid fluorescent composition to modify the luminescent color and the viscosity of the liquid fluorescent composition. The liquid fluorescent composition can be formed on the light emitting element (such as blue LED chip) by various processes such as an ink-jet printing, screen printing, coating, casting, priming, or dispensing process, thereby constituting a fluorescent layer (the liquid fluorescent composition can be coated on the light emitting element to form a layer without curing). After encapsulating by a sealing element (such as a glass optical lens), a white source or a composite light source with a simple process can be provided. 
     The components and amounts of the liquid fluorescent composition are discussed in detail below. 
     The liquid fluorescent composition or the invention substantially includes: 
     (a) 0.001-2 parts by weight of a fluorescent material, or preferably 0.01-1 parts by weight; and 
     (b) 100 parts by weight of a cyclic solvent. 
     Further, the liquid fluorescent composition can optionally include: 
     (c) 1-50 parts by weight of a color modifying agent, or preferably 3-40 parts by weight; and 
     (d) 0.02-5 parts by weight of a hindered amine light stabilizer (HALS), or preferably 0.5-2 parts by weight. 
     The aforementioned (a) fluorescent material can include a fluorescent polymer, a fluorescent dye, or combinations thereof. The fluorescent polymer can be a fluorene derivative copolymer with modifiable luminescent color and high luminescent efficiency, such as compounds copolymerized by 9,9-Dialkyl-fluorene (as a core) and aromatic molecules with high fluorescence. The fluorescent polymer can be prepared by fluorene derivative monomer and at least one molecule with conjugated groups (such as a phenyl group, a naphthyl group, a heterocyclic group, a multi-ring aromatic group, or a multi-ring heterocyclic group), as shown in formula (I): 
     
       
         
         
             
             
         
       
     
     wherein Ar 1 , Ar 2 , and Ar 3  are each independently selected from: 
     
       
         
         
             
             
         
       
     
     wherein, R 1 -R 12  are each independently hydrogen, hydroxyl group, C 1 -C 22  linear or branched alkyl group, C 1 -C 22  linear or branched alkoxy group, ortho-, meta-, or para-alkyl phenyl, or ortho-, meta-, or para-alkoxy phenyl, m, n, p, q of formula (I) is the number of repeated units, and the ratio of m to m+n+p+q is at least more than 0.1, or preferably more than 0.5. In embodiments of the invention, one or two of n, p, and q can be zero. 
     Further, the fluorescent polymer can include a poly(p-phenylene vinylene) (PPV) polymer as shown in formula (III): 
     
       
         
         
             
             
         
       
     
     wherein, R 13 -R 15  are each independently C 1 -C 22  linear or branched alkyl group, ortho-, meta-, or para-alkyl phenyl, or ortho-, meta-, or para-alkoxy phenyl, and a, b of formula (III) is the number of repeated units. Depending on the desired luminescent color, one of a and b can be zero (such as DB-PPV with green luminescence). When the ratio of a to a+b is at least more than 0.5 (preferably more than 0.8), the fluorescent polymer has yellow luminescence. 
     In addition to the fluorescent polymer, the (a) fluorescent material can also be a fluorescent dye, such as coumarin 6, fluorescein, acridine, 4-(Dicyanomethylene)-2-methyl-6-[p-(dimethylamino)-styryl]-4H-pyran, nitrostilbene, nitrobenzoxadiazole, riboflavin, rhodamine, or combinations thereof. 
     In an embodiment, the (a) fluorescent material has an ultraviolet-visible (UV-Vis) absorption spectrum at 440-470 nm wavelength corresponding to the emission wavelength of blue LEDs. In other embodiments, the (a) fluorescent material can have an absorption spectrum at other wavelengths corresponding to various light sources. 
     In the invention, the (a) fluorescent material serves as a fluorescent emitter. When the (a) fluorescent material is dissolved in a (b) cyclic solvent, the conjugated structure of the (b) cyclic solvent can produce resonance with the conjugated moieties of the (a) fluorescent material, thereby reducing the energy gap. Therefore, the red-shift degree of luminescence can be controlled by adjusting the conjugated degree of the (b) cyclic solvent, resulting in the desired luminescent color. 
     It should be noted that the (b) cyclic solvent must have a boiling point above 100° C., including a non-conjugated solvent (such as methylcyclohexane, decahydronaphthalene, or combinations thereof), a partially conjugated solvent (such as cyclohexylbenzene, 1,2,3,4-tetrahydronaphthalene, anisole, phenetole, ethylbenzene, propylbenzene, cumene, or combinations thereof), or a fully conjugated solvent (such as toluene, xylene, tri-methyl benzene (TMB), methylnaphthalene, dimethylnaphthalene or combinations thereof). The structure and the characteristic of a part of cyclic solvents are listed in Table 1. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 cyclic solvent 
                 structure 
                 bp(° C.) 
                 n d   
               
               
                   
                   
               
             
            
               
                   
                 non-conjugated solvent 
                                   
   Methylcyclohexane 
                 101   
                 1.422  
               
               
                   
                   
               
               
                   
                   
                                   
   Decahydronaphthalene 
                 188   
                 1.475  
               
               
                   
                   
               
               
                   
                 partially conjugated solvent 
                                   
   Cyclohexylbenzene 
                 239   
                 1.526  
               
               
                   
                   
               
               
                   
                   
                                   
   Tetrahydronaphthalene 
                 206   
                 1.541  
               
               
                   
                   
               
               
                   
                   
                                   
   Anisole 
                 153.7 
                 1.5174 
               
               
                   
                   
               
               
                   
                 fully conjugated solvent 
                                   
   Toluene 
                 111   
                 1.4967 
               
               
                   
                   
               
               
                   
                   
                                   
   o-Xylene 
                 144   
                 1.505  
               
               
                   
                   
               
               
                   
                   
                                   
   Tri-methyl benzene 
                 168   
                 1.504  
               
               
                   
                   
               
               
                   
                   
                                   
   1-Methylnaphthalene 
                 242   
                 1.615  
               
               
                   
                   
               
            
           
         
       
     
     Further, in the invention, a (c) color modifying agent can be optionally added into the liquid fluorescent composition. The (c) color modifying agent can have a cyclic molecule structure and be dissolved in the (b) cyclic solvent and include non-conjugated molecules, partially conjugated molecules, fully conjugated molecules, or combinations thereof. The non-conjugated color modifying agent can be cycloolefin copolymer (m-COC). The partially conjugated color modifying agent can be polystyrene (PS). The fully conjugated color modifying agent can be biphenylene, or naphthalene. The structure and the characteristic of some color modifying agents are listed in Table 2. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 color 
                   
                   
                   
               
               
                 modifying 
                   
                 mp or  
                   
               
               
                 agent 
                 structure 
                 Tg (° C.) 
                 nd 
               
               
                   
               
             
            
               
                 non- conjugated molecules 
                                   
   m-COC 
                 Tg = 161.4 (Topas  6015) 
                 1.52  (Topas  6015) 
               
               
                   
               
               
                 partially conjugated molecules 
                                   
   PS 
                 Tg = 94  (80  G/CM) 
                 1.59  (80  G/CM) 
               
               
                   
               
               
                 fully conjugated molecules 
                                   
   Biphenylene 
                 mp = 70 
                 — 
               
               
                   
               
               
                   
                                   
   Naphthalene 
                 mp = 81 
                 1.582 
               
               
                   
               
            
           
         
       
     
     The luminescent color of the liquid fluorescent composition can be modified by adjusting the conjugated degree of the color modifying agent, thereby precisely achieving the desired luminescent color such as 550 nm and enhancing the luminescent efficiency. 
     Further, the color modifying agent can be used to adjust the viscosity of the liquid fluorescent composition, facilitating the liquid fluorescent composition to form a layer by various processes. The viscosity of the liquid fluorescent composition can be of between 1 to 50,000 cps (at a temperature of 25° C.). 
     In general, in absence of the (c) color modifying agent, the liquid fluorescent composition having lower viscosity (1-20 cps at a temperature of 25° C.) is suitable to be formed into a layer by an ink-jet printing and priming process. After adding the (c) color modifying agent, the liquid fluorescent composition would have a medium viscosity (10-1000 cps at a temperature of 25° C.) suitable to be formed into a layer by a coating process, or a higher viscosity (500-50,000 cps at a temperature of 25° C.) suitable to be formed into a layer by a screen printing or dispensing process. 
     In an embodiment, the liquid fluorescent composition can absorb a light with a first wavelength (440-460 nm) emitted by a blue light source, and converts the light with a first wavelength to a light with a second wavelength (such as 530-700 nm). The light with a first wavelength and the light with a second wavelength can be mixed to serve as a white light source. Alternatively, the light with a first wavelength (440-460 nm) can convert completely to the light with a second wavelength (such as green lights, yellow lights, or red lights). 
     Moreover, the liquid fluorescent composition of the invention can include optionally a hindered amine light stabilizer (HALS) to improve the stability thereof. The hindered amine light stabilizer (HALS) can include bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, n-methyl-1-butanamin, or combinations thereof. 
     The following description with reference to  FIG. 1  is intended to illustrate application of the liquid fluorescent composition as disclosed in the invention.  FIG. 1  is a schematic diagram of a light emitting device  100  according to an embodiment of the invention. The light emitting device  100  includes a substrate  200  (such as a ceramic carrier) and a light emitting element  210  disposed on the substrate  200 . The type of the light emitting element  210  can be (but is not limited to) an inorganic light-emitting diode, a laser diode, or an organic light-emitting diode. In an embodiment, the light emitting element  210  includes a blue light emitting chip of GaN or GaInN. 
     The liquid fluorescent composition  220  can be disposed on the light-emitting element  210  by an ink-jet printing, screen printing, coating, casting, priming, or dispensing process, serving as a fluorescence converting layer (without curing). A sealing element  230 , such as a glass or plastic cap, is provided to encapsule the liquid fluorescent composition  220  into the chamber  240 . The liquid fluorescent composition  220  can absorb a light with a first wavelength emitted by the light-emitting element  210  and convert the light with a first wavelength to a light with a second wavelength. Further, the light with a first wavelength and the light with a second wavelength can be mixed to serve as a white irradiance. Therefore, a white light source (or a composite light source) with high light efficiency can be provided. 
     Before forming the liquid fluorescent composition  220  on the light-emitting element  210 , a transparent protection layer  250  can be formed on the light-emitting element  210 , separating the light-emitting element  210  from the liquid fluorescent composition  220 . Therefore, the performance of the light-emitting element  210  is adversely influenced by the direct contact of the liquid fluorescent composition  220 . The transparent protection layer  250  can be epoxy resin, acrylic resin, or polyvinyl acetate resin and has a thickness of between 0.1-1.0 μm. 
     Referring to  FIG. 1 , the substrate  200  is a cup-shaped substrate and the liquid fluorescent composition  220  is encapsuled into the chamber  240 , wherein the sealing element  230  and the substrate  200  together define the chamber  240 . In other embodiments, the substrate  200  can be substrates having a cavity with various shapes or a planar substrate. Further, the sealing element  230  can be a transparent plate case, rather than a lens-shaped sealing element. When the sealing element is a transparent plate case, the liquid fluorescent composition is primed into the space of the transparent plate case. After sealing, packaging and combining with a blue-emission back light source, a planar light source can be provided. 
     In addition, various sized bubbles or incompatible transparent liquid can be disposed into the chamber to form floating and transparent circular bubble/vacuoles. After combining with a blue (or other color) back light, an artistic totem light source is provided. The viscosity of the incompatible transparent liquid can be different from that of the liquid fluorescent composition. Alternatively, the incompatible transparent liquid can be other liquid fluorescent compositions with different emission wavelengths. 
     Accordingly, The emission wavelength of the liquid fluorescent composition of the invention can be modified by adjusted the conjugated proportion of the (b) cyclic solvent and the (c) color modifying agent, resulting in the desired luminescent color and increased luminescent efficiency. 
     Since the liquid fluorescent composition can be used to form a layer by a single process without further curing, the method for forming a layer of the liquid fluorescent composition is simple. Since the liquid fluorescent composition is a homogeneous liquid mixture, the problem resulting from non-uniform distribution of fluorescent powder is eliminated. In an embodiment, a white light source having a luminous efficacy of 96 Lm/W and a correlated color temperature of 4358K (warm color) or having a luminous efficacy of 98 Lm/W and a correlated color temperature of 6452K (pure white) can be provided by combining the liquid fluorescent composition of the invention and a light emitting element. In some embodiments, the color rendering index (CRI) of the liquid fluorescent composition exceeds that of inorganic LED (such as Blue LED) incorporated with phosphor YAG (CRI=70), providing a light source having a color rendering index of about 84. 
     The preparation of components of the liquid fluorescent composition, the liquid fluorescent composition of the examples, and the related measurement results of the light emitting device employing the liquid fluorescent composition of the examples are described in detail as below: 
     Prepared Example 1 
     Synthesis of Monomer m1 
     Monomer m1: 9,9-dioctyl-2,7-dibromofluorene 
     
       
         
         
             
             
         
       
     
     10 g of 2,7-dibromofluorene (Aldrich, 97%) was added into a reaction bottle. 175 ml of DMSO (ACROS), 8 g of potassium t-butoxide (Aldrich), and 19 g octylbromide (Aldrich) were added into the reaction bottle at a temperature of 45° C. After reaction for 24 hr, the result was diluted using ethyl acetate. 
     100 ml of water was used three times for extraction, and then the organic layers were combined, dried by magnesium sulfate, and concentrated, giving a white solid (15 g), and then purified by re-crystallization using an IPA (ACROS), giving acicular crystals of monomer m1 (13.25) with a yield of 77%.  1 H NMR (400 MHz, CDCl 3 ): δ (ppm) 7.51 (d, 2H), 7.45 (d, 2H), 7.44 (dd, 2H), 1.91 (t, 4H), 1.22-1.05 (m, 24H), 0.83 (t, 6H). 
     Prepared Example 2 
     Synthesis of Monomer m2 
     Monomer m2: 9,10-Dibromoanthracene (CAS No. 523-27-3) 
     
       
         
         
             
             
         
       
     
     9,10-Dibromoanthracene, from Aldrich Co., was purified by re-crystallization. 
     Prepared Example 3 
     Synthesis of Monomer m3 
     Monomer m3: 4,7-Dibromo-benzothiadiazole 
     
       
         
         
             
             
         
       
     
     13.6 g of benzothiadiazole (CAS:273-13-2, Aldrich) was added into a reaction bottle and dissolved by 100 ml of dichloromethane (Merck). After stirring completely, 60 ml of HOAc (Merck) was added into the reaction bottle at room temperature. Next, 50 ml of acetic acid and 40 ml of bromine water (Br 2 , Merck) were added dropwise into the reaction bottle. After an over night reaction period, the result was filtrated, and precipitate collected was washed by ether and then purified by re-crystallization using an IPA (ACROS), giving acicular crystals of monomer m3.  1 H NMR (400 MHz, CDCl 3 ):8 (ppm) 7.724 (s, 2H). 
     Prepared Example 4 
     Synthesis of Monomer m4 
     Monomer m4: 4,7-Bis-(5-bromo-thiophen-2-yl-benzo[1,2,5]thiadiazole) 
     
       
         
         
             
             
         
       
     
     1 g of 4,7-dibromo-2,1,3-benzothiadiazole (monomer m3, 3.4 mmole), 3.06 g 2-(tributylstannyl) thiophene (8.2 mmole) and 0.0477 g Pd(PPh 3 ) 2 Cl 2  (0.068 mmole) were added into a reaction bottle and dissolved by 25 ml of THF. After heating for reflux for 3 hours, the result was cooled down to terminate the reaction. After drying the THF, the result was purified by column separation, giving 0.71 g of a product of 4,7-dithien-2-yl-2,1,3-benzothiadiazole, with a yield rate of 69%. 
     3 grams of 4,7-dithien-2-yl-2,1,3-benzothiadiazole, 30 ml of CH 2 Cl 2  (Aldrich) were stirred till dissolved, and a mixed solution of 20 ml of HOAc and 4 ml of Br 2  (Merck) were slowly added at a room temperature for reaction for 18 hours, and the precipitate was washed with water, and re-precipitated with CH 2 Cl 2 , giving a black red solid of monomer m4.  1 H NMR (400 MHz, CDCl 3 ): δ (ppm) 7.787 (d, 4H, 4.0 Hz), 7.140 (d, 2H, 4 Hz). 
     Prepared Example 4 
     Synthesis of Monomer m4 
     Monomer m5: 1,4-Bisbromomethyl-2,3-dibutoxy benzene 
     
       
         
         
             
             
         
       
     
     118.5 grams of Morpholine (Aldrich), 41 grams of formaldehyde (Merck), 500 ml of IPA (ACROS) were placed in a 1000 ml dual-neck vase, heated to 95° C., and added 50 grams of catechol (TCI), at a temperature of 95° C. for reaction for 2.5 hours. 100 ml of EA (ACROS) was added at room temperature, stirred for 30 minutes, and filtered, giving a solid, and added 300 ml of EA, heated to 60° C., stirred, cooled down, filtered, and washed with EA, giving 82 grams of a solid DBI, with a yield rate of 58.6%. 
     56.5 grams of DBI, 1000 ml of EtOH (99.5%, Merck), 100 g of K 2 CO 3  (Aldrich), and 113 grams of n-butyl bromide (Aldrich) were added to a reaction bottle, heated to a reflux temperature for reaction for 69 hours, then filtered, concentrated, and dried. 500 ml of EA was added to the reaction bottle, extracted with water, dried with MgSO 4 , filtered, and concentrated, giving 66.36 g of a brown liquid (DB2), with a yield rate of 86.1%. 
     66.36 g of DB2, 210 ml of CH3COOH (ACROS), 91 g of CH 3 COONa (Aldrich), and 105 ml of acetic anhydride (Merck) were placed in a 1000 ml dual-neck bottle, heated to 103° C. for reaction for 89 hours, extracted with water and EA, dried with MgSO 4 , filtered, and concentrated, giving 65.24 grams of a brown liquid (DB3). 200 ml of HBr (33% in glacial acetic acid, Aldrich) was added to the dual-neck bottle, and reacted at room temperature for 2.5 hours. The reaction solution was extracted with water and EA, dried with MgSO 4 , filtered, and concentrated, giving 64.4 grams of a brown liquid, and then decolored by active carbon, and re-crystallized with methanol, giving a white solid of monomer m5.  1 H NMR (400 MHz, CDCl 3 ): δ (ppm) 7.082 (s, 2H), 4.519 (s, 4H), 4.086 (t, 4H, 6.7 Hz), 1.798 (m, 4H), 1.534 (m, 4H), 1.002 (t, 6H, 7.3 Hz). 
     The following reaction scheme illustrates the preparation of the monomer m5: 
     
       
         
         
             
             
         
       
     
     Prepared Example 6 
     Synthesis of Monomer m6 
     Monomer m6: 2,5-Bis(bromomethyl)-1-methoxy-4-(2-ethylhexyloxy)benzene (CAS No. 2096255-56-2) 
     
       
         
         
             
             
         
       
     
     2,5-Bis(bromomethyl)-1-methoxy-4-(2-ethylhexyloxy)benzene, from Aldrich Co., was purified by re-crystallization. 
     Prepared Example 7 
     Synthesis of Fluorene Fluorescent Polymer 
     The green, yellow, and red fluorescent polymers were copolymerized through Yamamoto coupling reaction, using the monomer m1 as the major molecule combined with the monomers m3˜m4. The polymerization method for a yellow fluorene copolymer is described in detail below, wherein the other copolymers such as green and red fluorescent polymers are copolymerized by the same method. 
     Under de-gas water, 2.91 g of Bis(1,5-cyclooctadiene)Nickle, (10.59 mmole, Ni(COD) 2 , Stream), 1.65 g 2,2-Bipyridyl (BPY, Aldrich), 1.3 ml cis,cis-1,5-Cyclooctadiene (10.59 mmole COD, Aldrich), and 5 ml anhydrous THF (Merk) were placed in a 50 ml reaction bottle, heated to 80° C., stirred for 30 minutes, and under nitrogen, the monomer dissolved in anhydrous and THF was added to the mixture. 
     The types and ratio of the monomers used was m1:m2:m3:m4=50 (2.75 g, 5 mmole):32.4 (0.96 g, 3.24 mmole):17.5 (0.58 g, 1.75 mmole):0.1 (0.04 g, 0.1 mole), and the mixture was reacted at a temperature of 80° C. for two days, and then 0.15 g of 4-tert-butylbenzyl bromide (0.7 mmole, Aldrich), and 10 ml of anhydrous THF were added for reaction for 24 hours. After the reaction was completed, the result was put into 1000 ml of THF, and 1 c.c. of HCl was added and stirred for 2 hours, filtered, and column separated to remove the metal catalyst. The resulting product was re-precipitated with methanol, washed by methanol, and vacuum dried to remove the remaining solvent, giving an orange solid of about 0.8 grams, with a yield rate of 40%. GPC:Mw=42K dalton, PDI=2.7. UV absorb peak (UV-Vis, film) was 434 nm, and PL peak was about 525 nm (excited at 450 nm wavelength). 
     The structure and the ratio between the repeated units (m, n, p, and q) of the obtained yellow, green and red fluorescent polymers are shown below: 
     
       
         
         
             
             
         
       
     
     Red fluorescent polymer, m:n:p:q=50:17.5:30:2.5 
     Yellow fluorescent polymer, m:n:p:q=50:17.5:32.4:0.1 
     Green fluorescent polymer, m:n:p:q=50:17.5:32.5:0 
     Prepared Example 8 
     Synthesis of PPV Fluorescent Polymer 
     The green, yellow, and orange fluorescent polymers were copolymerized through Gilch dehydrohalogenation condensation polymerization, using the monomers m5 and m6 with different ratios to form green, yellow, and orange fluorescent polymers. 
     3 g of m5 monomer (7.4 mmole) and 0.158 g of m4 monomer (0.39 mmole) were placed in a tetra-neck vase, baked to dry, and under nitrogen, 300 ml of anhydrous THF was added, stirred until dissolved, giving a transparent colorless liquid. 60 ml of t-BuOK(Aldrich, conc.1M in THF) was added to the tetra-neck vase, giving a yellow solution, and under nitrogen, left at room temperature for reaction for 24 hours (Gilch dehydrohalogenation condensation polymerization), giving a yellow-green fluorescent dense liquid. The high viscous liquid was slowly put in a cup of MeOH, giving an orange gel, and filtered, and put in a vase to vacuum dry, giving an orange fiber-shaped solid. The orange fiber-shaped solid was dissolved in the THF again, and dripped slowly in a cup of MeOH, giving a gel, filtered, and put in a bottle to vacuum dry, giving an orange fiber-shaped solid of DB-MEH-PPV copolymer with a weight average molecular weight (Mw) of about 770 k Dalton, PDI=4.2. UV-Vis Absorb spectrum (film) of 467, 497 nm, and PL spectrum (film) of 556 nm (excited at 450 nm wavelength). 
     The structure of the obtained copolymer is shown below: 
     
       
         
         
             
             
         
       
     
     a and b are the number of repeated units. 
     DB-PPV and MEH-PPV as shown below were prepared by modifying the above steps: 
     
       
         
         
             
             
         
       
     
     n is the number of repeated units. 
     Example 1 
     Yellow Fluorene Copolymer Liquid Fluorescent Composition 
     Liquid fluorescent compositions were prepared according to Table 3. The ultraviolet-visible (UV-Vis) absorption spectrum of the obtained liquid fluorescent compositions were respectively measured by a JASCO V-530 UV-Vis spectrophotometer, and the emission wavelength (PL) of the obtained liquid fluorescent compositions were respectively measured by an FL4500/Hitachi Fluorescence spectrophotometer (excited at 450 nm wavelength), and the results are shown in Table 3. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 color modifying 
                 fluorescent 
                 cyclic 
                   
                   
               
               
                 agent 
                 material 
                 solvent 
               
               
                 (10 parts by 
                 (0.05 parts by 
                 (100 parts by 
                 UV 
                 PL 
               
               
                 weight of) 
                 weight of) 
                 weight of) 
                 (nm) 
                 (nm) 
               
               
                   
               
             
            
               
                 cycloolefin 
                 — 
                 1-methyl 
                 — 
                 — 
               
               
                 copolymer 
                   
                 naphthalene 
               
               
                 cycloolefin 
                 yellow 
                 methyl- 
                 435 
                 529.4 
               
               
                 copolymer 
                 fluorescent 
                 cyclohexane 
               
               
                   
                 polymer of 
               
               
                   
                 Prepared 
               
               
                   
                 Example 7 
               
               
                 cycloolefin 
                 yellow 
                 decahydro- 
                 437 
                 535.0 
               
               
                 copolymer 
                 fluorescent 
                 naphthalene 
               
               
                   
                 polymer of 
               
               
                   
                 Prepared 
               
               
                   
                 Example 7 
               
               
                 cycloolefin 
                 yellow 
                 cyclohexane 
                 450 
                 540.2 
               
               
                 copolymer 
                 fluorescent 
                 benzene 
               
               
                   
                 polymer of 
               
               
                   
                 Prepared 
               
               
                   
                 Example 7 
               
               
                 cycloolefin 
                 yellow 
                 1-methyl 
                 451 
                 543.0 
               
               
                 copolymer 
                 fluorescent 
                 naphthalene 
               
               
                   
                 polymer of 
               
               
                   
                 Prepared 
               
               
                   
                 Example 7 
               
               
                 polystyrene 
                 yellow 
                 trimethyl 
                 449 
                 542.8 
               
               
                   
                 fluorescent 
                 benzene 
               
               
                   
                 polymer of 
               
               
                   
                 Prepared 
               
               
                   
                 Example 7 
               
               
                 polystyrene 
                 yellow 
                 cyclohexane 
                 449 
                 541.3 
               
               
                   
                 fluorescent 
                 benzene 
               
               
                   
                 polymer of 
               
               
                   
                 Prepared 
               
               
                   
                 Example 7 
               
               
                 polystyrene 
                 yellow 
                 1-methyl 
                 452 
                 549.8 
               
               
                   
                 fluorescent 
                 naphthalene 
               
               
                   
                 polymer of 
               
               
                   
                 Prepared 
               
               
                   
                 Example 7 
               
               
                 naphthalene 
                 — 
                 1-methyl 
                 — 
                 — 
               
               
                   
                   
                 naphthalene 
               
               
                 naphthalene 
                 yellow 
                 methyl- 
                 446 
                 537.6 
               
               
                   
                 fluorescent 
                 cyclohexane 
               
               
                   
                 polymer of 
               
               
                   
                 Prepared 
               
               
                   
                 Example 7 
               
               
                 naphthalene 
                 yellow 
                 decahydro- 
                 450 
                 537.6 
               
               
                   
                 fluorescent 
                 naphthalene 
               
               
                   
                 polymer of 
               
               
                   
                 Prepared 
               
               
                   
                 Example 7 
               
               
                 naphthalene 
                 yellow 
                 cyclohexane 
                 449 
                 541.8 
               
               
                   
                 fluorescent 
                 benzene 
               
               
                   
                 polymer of 
               
               
                   
                 Prepared 
               
               
                   
                 Example 7 
               
               
                 naphthalene 
                 yellow 
                 1-methyl 
                 456 
                 552.8 
               
               
                   
                 fluorescent 
                 naphthalene 
               
               
                   
                 polymer of 
               
               
                   
                 Prepared 
               
               
                   
                 Example 7 
               
               
                 — 
                 yellow 
                 1-methyl 
                 453 
                 553.6 
               
               
                   
                 fluorescent 
                 naphthalene 
               
               
                   
                 polymer of 
               
               
                   
                 Prepared 
               
               
                   
                 Example 7 
               
               
                   
               
            
           
         
       
     
     As shown in Table 3, the absorption wavelengths and emission wavelengths of the liquid fluorescent compositions including yellow fluorescent polymer can be modified by adjusting the proportion of the cyclic solvent and color modifying agent therein. 
     Example 2 
     Other Color Liquid Fluorescent Composition 
     Liquid fluorescent compositions were prepared according to Table 4. The ultraviolet-visible (UV-Vis) absorption spectrum of the obtained liquid fluorescent compositions were respectively measured by a JASCO V-530 UV-Vis spectrophotometer, and the emission wavelength (PL) of the obtained liquid fluorescent compositions were respectively measured by an FL4500/Hitachi Fluorescence spectrophotometer (excited at 450 nm wavelength), and the results are shown in Table 4. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                 color modifying 
                 fluorescent 
                 cyclic 
                   
                   
               
               
                 agent 
                 material 
                 solvent 
               
               
                 (10 parts by 
                 (0.05 parts by 
                 (100 parts by 
                 UV 
                 PL 
               
               
                 weight of) 
                 weight of) 
                 weight of) 
                 (nm) 
                 (nm) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 — 
                 green 
                 methyl- 
                 433 
                 524 
               
               
                   
                 fluorescent 
                 cyclohexane 
               
               
                   
                 polymer of 
               
               
                   
                 Prepared 
               
               
                   
                 Example 7 
               
               
                 polystyrene 
                 green 
                 toluene 
                 437 
                 533.4 
               
               
                   
                 fluorescent 
               
               
                   
                 polymer of 
               
               
                   
                 Prepared 
               
               
                   
                 Example 7 
               
               
                 — 
                 green 
                 1-methyl 
                 455 
                 543 
               
               
                   
                 fluorescent 
                 naphthalene 
               
               
                   
                 polymer of 
               
               
                   
                 Prepared 
               
               
                   
                 Example 7 
               
               
                 — 
                 red fluorescent 
                 MeCHex 
                 438 
                 529 
               
               
                   
                 polymer of 
               
               
                   
                 Prepared 
               
               
                   
                 Example 7 
               
               
                 polystyrene 
                 red fluorescent 
                 toluene 
                 444 
                 532.4, 
               
               
                   
                 polymer of 
                   
                   
                 625.4 
               
               
                   
                 Prepared 
               
               
                   
                 Example 7 
               
               
                 — 
                 red fluorescent 
                 1-methyl 
                 455 
                 625.4 
               
               
                   
                 polymer of 
                 naphthalene 
               
               
                   
                 Prepared 
               
               
                   
                 Example 7 
               
               
                   
                 DB-PPV 
                 toluene 
                 445 
                 524 
               
               
                 — 
                 DB-PPV 
                 1-methyl 
                 447 
                 534.6 
               
               
                   
                   
                 naphthalene 
               
               
                   
                 MEH-PPV 
                 toluene 
                 495 
                 572 
               
               
                 — 
                 MEH-PPV 
                 1-methyl 
                 500 
                 585 
               
               
                   
                   
                 naphthalene 
               
               
                 — 
                 coumarin-6 
                 THF 
                 460 
                 490 
               
               
                 — 
                 coumarin-6 
                 1-methyl 
                 465 
                 536 
               
               
                   
                   
                 naphthalene 
               
               
                   
               
            
           
         
       
     
     As shown in Table 4, the absorption wavelength and emission wavelength of the liquid fluorescent compositions including fluorescent polymer or fluorescent dye can be modified by adjusting the proportion of the cyclic solvent and color modifying agent therein. 
     Example 3 
     Fabrications of White, Green, and Red LEDs 
     0.02 parts by weight of yellow fluorescent polymer of Prepared Example 7, 0.5 parts by weight of green fluorescent polymer of Prepared Example 7, and 0.5 parts by weight of red fluorescent polymer of Prepared Example 7 were dissolved in 100 parts by weight of TMB. Next, 10 parts by weight of polystyrene (PS/80G Chimei) was added into the above mixture, giving a liquid fluorescent composition 1. 
     0.5 parts by weight of green fluorescent polymer of Prepared Example 7 was dissolved in 100 parts by weight of TMB. Next, 10 parts by weight of polystyrene (PS/80G Chimei) was added into the above mixture, giving a liquid fluorescent composition 2. 
     0.5 parts by weight of red fluorescent polymer of Prepared Example 7 was dissolved in 100 parts by weight of TMB. Next, 10 parts by weight of polystyrene (PS/80G Chimei) was added into the above mixture, giving a liquid fluorescent composition 3. 
     The liquid fluorescent compositions 1-3 were respectively coated on a Cree GaN blue LED chip with a protection layer of polyvinyl alcohol by a dispensing process. Next, the luminescent efficiency, correlated color temperature (CCT), and CIE color coordination of the obtained devices were measured by an integrating-sphere photometer under a current of 20 mA, and the results are shown in Table 5. 
     The liquid fluorescent compositions 1-3 were respectively dropped into a glass lens, and the glass lens was sealed with a Cree GaN blue LED chip. Next, the luminescent efficiency, correlated color temperature (CCT), and CIE color coordination of the obtained devices were measured by an integrating-sphere photometer under a current of 20 mA, and the results are shown in Table 5. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                   
                   
                   
                   
                 directly 
                 encapsulating 
               
               
                   
                   
                   
                   
                 formed on the 
                 with glass 
               
               
                 I (A) 
                 V 
                 CCT &amp; CIE 
                 lm 
                 chip (lm/W) 
                 lens (lm/W) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 0.02 
                 2.716 
                 4358K 
                 6.806 
                 125.3 
                 135 
               
               
                   
                   
                 (warm white) 
               
               
                 0.02 
                 2.714 
                 CIE = 0.36, 
                 9.2931 
                 172 
                 184 
               
               
                   
                   
                 0.59 (Green) 
               
               
                 0.02 
                 2.716 
                 CIE = 0.56, 
                 1.037 
                 19.1 
                 20.6 
               
               
                   
                   
                 0.32 (Red) 
               
               
                   
               
            
           
         
       
     
     Example 4 
     White LEDs with Various CCTs 
     Yellow fluorescent polymer of Prepared Example 7, 0.5 parts by weight of green fluorescent polymer of Prepared Example 7, and 0.5 parts by weight of red fluorescent polymer of Prepared Example 7 were dissolved in 100 parts by weight of 1-methyl naphthalene, wherein the amount of the yellow fluorescent polymer of Prepared Example 7 was adjusted according to Table 6. Next, 10 parts by weight of naphthalene was added into the above mixture; giving a liquid fluorescent compositions. 
     The liquid fluorescent compositions were respectively dropped into a glass lens, and the glass lens was sealed with a Cree GaN blue LED chip. Next, the luminous flux, luminescent efficiency, correlated color temperature (CCT), and CIE color coordination of the obtained devices were measured by an integrating-sphere photometer under a current of 20 mA, and the results were shown in Table 6. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 6 
               
               
                   
               
               
                 Yellow fluorescent 
                 lumi- 
                 lumines- 
                 CIE color 
                   
                 Excita- 
               
               
                 polymer of Pre- 
                 nous 
                 cent ef- 
                 coordi- 
                   
                 tion wave- 
               
               
                 pared Example 7 
                 flux 
                 ficiency 
                 nation 
                   
                 length 
               
               
                 (parts by weight) 
                 (lm) 
                 (lm/W) 
                 (CIE x, y) 
                 CCT 
                 (nm) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 0.005 
                 5.54 
                 100.36 
                 0.315, 0.41  
                 9319 
                 540 
               
               
                 0.0063 
                 6.19 
                 112.14 
                 0.312, 0.395 
                 6201 
                 540 
               
               
                 0.0125 
                 6.84 
                 123.9 
                 0.355, 0.48  
                 5035 
                 540 
               
               
                 0.025 
                 7.1 
                 128.6 
                 0.406, 0.564 
                 4359 
                 540 
               
               
                 0.05 
                 6.94 
                 125.7 
                 0.421, 0.563 
                 4136 
                 542 
               
               
                   
               
            
           
         
       
     
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.