KEYWORDS: Light emitting diodes, Luminous efficacy, Coating, Light scattering, Blue light emitting diodes, Human vision and color perception, Silicon, Scanning electron microscopy, Photonics, Reliability
The emission-adaptive phosphor layer was fabricated by self-exposure method to realize the pc-white LED. The effect of phosphor layer forming parameters such as phosphor content, exposure intensity and exposure time on the phosphor layer shape and LED characteristics was investigated. Through the fabrication process of phosphor layer, two types of phosphor layer shape were fabricated by phosphor layer forming parameters. In the case of low exposure intensity and/or short exposure time with high phosphor content, the conformal coating shape phosphor layer which is imitative of the irradiance pattern of an LED chip was formed, whereas in the high exposure intensity and/or long exposure time with low phosphor content, the light distribution proportional shape phosphor layer which reflects the near-filed pattern of an LED chip was formed. Therefore the latter was superior to the former in the angular color homogeneity due to a strong similarity between the phosphor content distribution and the light intensity distribution of an LED chip in all directions. It was concluded that the object-oriented emission-adaptive phosphor layer closely similar to the light distribution proportional shape phosphor layer was formed in the condition of high exposure intensity and/or long exposure time with high phosphor content and resulted in high luminous efficacy, low correlated color temperature as well as high angular color homogeneity.
The influence of phosphor sedimentation on the white light-emitting diode with different structure chip was
investigated. The phosphor sedimentation phenomenon occurred seriously as encapsulant viscosity lowers. The influence
of phosphor sedimentation on the white light-emitting diode with the vertical structure chip whose one side only emits is
larger than that of lateral structure chip whose all sides emit. Hence, Difference in luminous efficacy by the phosphor
sedimentation reached about 20 % in the case with the vertical structure chip due to optical loss stemmed from the
phosphor sediment layer.
White light-emitting diodes (LEDs) have dramatically developed and gradually taken over from the conventional light
source as the solid-state lighting during the last decade. It is now sufficient for illumination application in performance,
while it is still insufficient in color quality. Especially, most of phosphor-converted white LEDs have the poor angular
color homogeneity. In this study, we adopted a distinctive phosphor conformal coating technique in the packaging
process to reduce the variance of correlated color temperature (CCT) among the packages and spatial CCT in the
package. Also, to reduce the spatial CCT variance without considerable shrinkage of luminous efficacy, we applied submicrometer
scale TiO2 powder as diffuser in the phosphor layer or in the encapsulation layer of white LED with a
phosphor conformal coating layer and investigated the effects of titania diffuser on angular color homogeneity and
optical performance. Regardless of the diffuser content, spatial CCT variance and luminous efficacy were decreased with
the increase of the diffuser content. Nevertheless, among the conditions for achievement of the equivalent in color
uniformity, the luminous efficacy in the case of 0.1 wt% diffuser mingled in the encapsulation layer was 20 % higher
than in the case of 5 wt% diffuser mingled in the phosphor layer. These phenomena result from differences of light
scattering loss caused by 10 times more volume of diffuser mixed in the phosphor layer than in the encapsulation layer.
A microlens is one of the most important components in optical microsystems. In the last decade, a lot of attempts have been done to fabricate a microlens or microlenses array, however, most of them are relatively complicated in the fabrication process and have difficulties in getting good surface roughness and realizing microlenses array. In this paper, we represent a very simple fabrication technology of the microlens or microlenses array which is based upon a deep X-ray exposure and a thermal treatment of a resist, usually PMMA. The molecular weight and Tg of PMMA is reduced when it is exposed to the deep X-ray. The microlens is produced through the effect of surface tension and reflow by adding a thermal treatment on the irradiated PMMA. A configuration of the microlens is determined by parameters such as absorbed X-ray dose on PMMA, heating temperature, and heating time in the thermal treatment. Diameters of the produced microlens range from 100 micrometers to 1500 micrometers and their changed heights are between 10 micrometers and 20 micrometers .
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