The Research Of White LED’s Color Rendering Index And Junction Temperature

Recently，the widely used white LEDs are fabricated with blue LED chipsand YAG yellow fluorescent powders. However, the Rendering Index of theseLEDs is low, as the spectrum of YAG yellow fluorescent powders is narrow. Forhigh level usage of white LEDs，it is urgent to increase the red composition ofspectrum and to improve the Rendering Index.This thesis focused on improving the Rendering Index of high power whiteLEDs through introducing red organic materials during the packing of blue LEDchips by YAG yellow fluorescent powders. Red organic material Ru(dtb-bpy)32(PF6) or MEHPPV was mixed with YAG yellow fluorescent powders or coatedto blue LED chips layer by layer alternately with YAG yellow powders. Thecurrent and junction temperature properties of these type LEDs were researchedand analyzed.We used the blue LED chip to excite the mixed fluorescent powder, includedRu(dtb-bpy)32(PF6) and YAG. Studied on the changes of White LED’ spectralproperties with the increasing of the Ru(dtb-bpy)32(PF6)’concentration, TheWhite LED color-rending index reached83.2, and the luminous efficiency wasabout20%lower relative to the Ru(dtb-bpy)32(PF6)’concentration of0%, whenthe Ru(dtb-bpy)32(PF6)’concentration was1.5%，moreover, we studied on theinfluence of junction temperature on the luminous properties of the integrationpackage White LED. The results showed that the blue chip radiation appearedrelatively substantially reduced, about27.73%lower, it also led to theattenuation of the wave peak that was synthesized by the two types of lightwhich the mixture fluorescent powder was excited to emit, and the luminousefficiency appeared substantially to reduce attenuation31.76%, but itscolor-rending is not obviously changed, during LED’s junction temperaturerising from30℃to130℃.The spectrum of white LED was studied and the color rendering index was improved respectively. Here, the Ru(dtb-bpy)32(PF6) was coated to the LEDchips, then the YAG phosphor on top of Ru(dtb-bpy)32(PF6). The weight ratioof Ru(dtb-bpy)32(PF6) was0%、2%、3%、4%relative to YAG respectively.From the results of ratio increasing, we found that the spectra properties changedand the color rendering index was improved to85when the ratio was2%.Moreover, we studied the Luminous properties by varying working current,analyzed in theory why the luminous flux increased and luminous efficiencydecayed gradually with the increasing of the sample’s working current.We fabricated White light LED Sample of NO.0to4, by putting0.0mg,1.0mg,3.0mg,4.0mg,5.5mg Ru(dtb-bpy)32(PF6) THF solution on the YAGpowder coating of the conservative White light LED, respectively, and analyzedthe spectra properties that Ru(dtb-bpy)32(PF6) materials was excited by theWhite light LED. The results showed that the White LED can excite theRu(dtb-bpy)32(PF6) materials. With the increase of the weight of theRu(dtb-bpy)32(PF6), the phosphor spectra appeared intensity attenuation andred shift. Both the luminous efficiency and color rending index of the samplesappeared to increase firstly, then decrease. Therefore, we can obtain the Whitelight LED with high luminous efficiency and high color rending index, thoughadjusting the content of the Ru(dtb-bpy)32(PF6) materials reasonably.The spectrum of white LED was studied and the color rendering index wasimproved respectively. Here, the MPPV was coated to the LED chips, then theYAG phosphor on top of MPPV. The weight ratio of MPVV was0%、1%、4%、6%relative to YAG respectively. We found that the peak increased significant inthe region of red light. The red region appeared radiation peak obviously and thecolor rendering index reached88when the ratio was4%. Moreover, we studiedand analyzed why MPPV can improve the CRI of White LED significantly basedon the standard calculation method of CRI, by contrasting to the eight standardtest color and the corresponding special color rendering index.