Abstract:
A backlight module includes a light guide plate, a light source, and a phosphor film. The light source is secured to the light guide and includes an emitting element and a phosphor element covering the emitting element. The phosphor film includes a plurality of colored phosphor particles. The emitting element emits light with a first primary color. A lighting path is defined by the phosphor element, the light guide plate, and the colored phosphor particles, and the resulting mixed-color light is converted to a white light to illuminate a display panel. A display device with the backlight module is also provided.

Description:
FIELD 
       [0001]    The subject matter herein generally relates to a backlight module and a liquid crystal device using the backlight module. 
       BACKGROUND 
       [0002]    In its basic form, a liquid crystal display (LCD) does not emit light and hence requires a backlight for its function as a visual display. Light Emitting Diodes (LEDs) have been employed as light sources for backlighting LCDs. However, if the LED&#39;s luminous efficiency is not high, the display by backlight module and the display device is reduced in visibility. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0003]    Implementations of the present technology will now be described, by way of example only, with reference to the attached figures. 
           [0004]      FIG. 1  is an exploded, isometric view of a first embodiment of a display device of the present disclosure. 
           [0005]      FIG. 2  is an assembled isometric view of the first embodiment of a display device of the present disclosure. 
           [0006]      FIG. 3  is a cross-sectional view of the display device of  FIG. 2 . 
           [0007]      FIG. 4  is a cross-sectional view of a second embodiment of a display device of the present disclosure. 
           [0008]      FIG. 5  is a cross-sectional view of a third embodiment of a display device of the present disclosure. 
           [0009]      FIG. 6  is a cross-sectional view of a fourth embodiment of a display device. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. The drawings are not necessarily to scale and the proportions of certain parts may be exaggerated to better illustrate details and features. The description is not to be considered as limiting the scope of the embodiments described herein. 
         [0011]    The term “substantially” is defined to be essentially conforming to the particular dimension, shape, or other feature that the term modifies, such that the component need not be exact. For example, “substantially cylindrical” means that the object resembles a cylinder, but can have one or more deviations from a true cylinder. The term “comprising” means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in a so-described combination, group, series and the like. 
         [0012]      FIG. 1  illustrates a first embodiment of a display device  100  of the present disclosure,  FIG. 2  illustrates the first embodiment of a display device  100  when assemble. The display device  100  includes a display panel  110 , and a backlight module  120  disposed under the display panel  110 . The backlight module  120  provides white light required as backlighting by the display panel  110 . The display panel  110  may be a liquid crystal display panel. The backlight module  120  includes a light guide plate  130 , a light source  140 , a phosphor film  150 , an optical film  160 , and a reflector  170 . 
         [0013]    The light guide plate  130  has a light incident surface  131 , a light emitting surface  132  adjacent to the light incident surface  131 , and a bottom surface  133  opposite to the light emitting surface  132 . The light source  140  is disposed beside the light incident surface  131 , the phosphor film  150  is disposed beside the light emitting surface  132 , and the reflector  170  is disposed beside the bottom surface  133 . The optical film  160  is disposed beside the phosphor film  150  away from the light guide plate  130  and sandwiched between the phosphor film  150  and the display panel  110 . 
         [0014]      FIG. 3  illustrates the display device  100  in cross section. In at least one embodiment, the light source  140  may be a light emitting diode comprising a package body  142 , an emitting element  141  fixed in the package body  142 , and phosphor element  143  distributed in the package body  142  and covering the emitting element  141 . It is understood that the phosphors  143  can be mixed with a base material  144  to form a sealing compound covering the emitting element  141 . The emitting element  141  is configured to provide light with a first primary color. In this embodiment, the emitting element  141  is a light emitting diode chip emitting blue light, and the first primary color is blue with wavelength of approximately 458-480 nanometers. The phosphors  143  and the emitting element  141  are integrally formed. The phosphors  143  may directly cover the emitting element  141  or may be disposed in the package body  142 , such that the light from the emitting element  141  is emitted through the phosphor element  143 . In this embodiment, the phosphors  143  have a second primary color, and the second primary color is red. In other words, the phosphors  143  may be red. The red phosphor material may include Mn 4+ or Eu 2+ , such as K 2 SiF 6 : Mn 4+ , Ca 2 Si 5 N 8 : Eu 2+ , Sr 2 Si 5 N 8 : Eu 2+ , Ca 2 AlSiN 3 : Eu 2+ , CaS: Eu 2+ . Mg 2 TiO 4 : Mn 4+ K 2 TiF 6 : Mn 4+ or others. 
         [0015]    A portion of the light with the first primary color excites the phosphors  143  to generate light with the second primary color. The light with the second primary color mixes with light of the first primary color such that the light source  140  emits a mixed light of the first primary color and the second primary color. In one embodiment, the emitting element  141  is a light emitting diode chip emitting blue light, the phosphors  143  is red, and the light source  140  thus emits mixed blue and red light. 
         [0016]    The mixed blue and red light passes through the light incident surface  131  into the light guide plate  130  and leaves the light guide plate  130  through the light emitting surface  132  to go out. The mixed blue and red light from the light emitting surface  132  of the light guide plate  130  is provided to the phosphor film  150 . The reflector  170  reflects light leaking from the bottom of the light guide plate  130  back to the light guide plate  130 . 
         [0017]    The phosphor film  150  may include a bottom barrier layer  151 , a top barrier layer  152 , and a phosphor layer  153  located between the bottom barrier layer  151  and the top barrier layer  152 . The bottom barrier layer  151  and the top barrier layer  152  protect the phosphor layer  153 . The phosphor layer  153  has base material  1531  and a plurality of phosphors  1532  located in the base material  1531 . The base material  1531  can be transparent, and the phosphors  1532  can output light of a third primary color. 
         [0018]    In this embodiment, the third primary color is green. In other words, the phosphor layer  153  is a green phosphor layer and has a plurality of green phosphors  1531 . The material of the green phosphors  1531  may include SrGa 2 S 4 : Eu 2+ , and the proportion of phosphors  1531  in the phosphor layer  150  can be range from 5%˜20%. Moreover, a thickness of the phosphor layer  153  can be in a range from 5˜50 um, and a thickness of each of the bottom barrier layer  151  and the top barrier layer  152  can be in a range from 5˜50 um. Accordingly, a thickness of the phosphor film  150  can be in a range from 15˜150 um. 
         [0019]    The optical film  160  may be a diffuser or a brightness enhancement film. In at least one embodiment, the optical film may not be required, and then white light emitted from the phosphor film  150  may be directed directly toward the display panel  110 . In this embodiment, the optical film  160  is a dual-brightness enhancement film (D-BEF) or a brightness enhancement film-reflective polarizer (BEF-RP). A part the mixed light from the light guide plate  130  excites the phosphor film  150  to generate white light, and the white light is provided to the display panel  110  via the optical film  160 . The other part of the mixed light from the light guide plate  130  is reflected to the light guide plate  130  by the optical film  160 , reflected by the reflector  170 , and as a second tranche is provided to the optical film  160 . Accordingly, the other part of the mixed light can be changed to white light by the optical film  160 , and the white light is provided to the display panel  110  via the optical film  160 . Each of the first primary color, the second primary color, and the third primary color are different, each being a monochrome color. 
         [0020]    The backlight module  120  generates white light when the light of the emitting element  141  excites the phosphor element  143  and the phosphor film  150 . 
         [0021]    The first light conversion in the light source  140  and the second light conversion in the phosphor film  150  are delivered substantially separate from each other, and the light conversion efficiency of the two conversions is thereby improved. Furthermore, because the optical film  160  can reflect part of the mixed light from the light guide plate  130  to the light guide plate  130  by the optical film  160 , and the light guide plate  130  and the reflector  170  can provide the other part of the mixed light to the optical film  160  as the second tranche, the light conversion efficiency of the backlight module  120  and the liquid crystal panel are also improved. Luminous efficiency and brightness the backlight module  120  and the liquid crystal panel are thus improved. 
         [0022]      FIG. 4  illustrates a second embodiment of a display device  200  of the present disclosure. The display device  200  includes a display panel  210 , and a backlight module  220  disposed under the display panel  210 . The display device  200  is similar to the display device  100  of the first embodiment but the display device  200  comprises two optical films  260  and  280 . The optical film  260  and the optical film  280  are disposed on the phosphor film  250  away from the light guide plate  230  and sandwiched between the display panel  210  and the phosphor film  250 . Each of the optical film  260  and the optical film  280  may be a diffuser or a brightness enhancement film. In this embodiment, the optical film  280  is a dual-brightness enhancement film (D-BEF) or a brightness enhancement film-reflective polarizer (BEF-RP), and the optical film  260  may be a diffuser or a brightness enhancement film. 
         [0023]      FIG. 5  illustrates a third embodiment of a display device  300  of the present disclosure. The display device  300  includes a display panel  310 , and a backlight module  320  disposed under the display panel  310 . The display device  300  is similar to the display device  100  of the first embodiment but the display device  300  comprises three optical films  360 ,  380 , and  390 . The optical film  360 , the optical film  380 , and the optical film  390  are disposed on the phosphor film  350  away from the light guide plate  330  and sandwiched between the display panel  310  and the phosphor film  350 . Each of the optical film  360 , the optical film  380 , and the optical film  390  may be a diffuser or a brightness enhancement film. In one embodiment, the optical film  390  is a dual-brightness enhancement film (D-BEF) or a brightness enhancement film-reflective polarizer (BEF-RP), and the optical films  360  and  380  may be a diffuser or a brightness enhancement film. 
         [0024]      FIG. 6  illustrates a fourth embodiment of a display device  400  of the present disclosure. The display device  400  includes a display panel  410 , and a backlight module  420  disposed under the display panel  410 . The display device  400  is similar to the display device  100  of the first embodiment but the display device  400  comprises five optical films  460 ,  470 ,  480 ,  490 , and  495 . The optical films  460 ,  470 ,  480 ,  490 , and  495  are disposed on the phosphor film  450  away from the light guide plate  430  and sandwiched between the display panel  410  and the phosphor film  450 . In one embodiment, the optical film  495  is an advanced polarizer film (APF) which can be attached to a lower surface of a display panel, and each of the optical films  460 ,  470 ,  480 , and  490  may be a diffuser or a brightness enhancement film. In detail, the display device  400  further comprises a top polarizer  411  and a lower polarizer  412 , these being disposed on two sides of the display panel  410 . The optical film  495  is attached to a lower surface of the lower polarizer  412 . Alternatively, the optical film  495 , functioning as an advanced polarizer film, can carry out the function of the lower polarizer  412 . The brightness enhancement structure of the advanced polarizer film can be integrated into the lower polarizer  412  to obtain an equivalent function. 
         [0025]    While various exemplary and preferred embodiments have been described the disclosure is not limited thereto. On the contrary, various modifications and similar arrangements (as would be apparent to those skilled in the art) are intended to also be covered. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.