Abstract
In comparison with the conformal phosphor or in-cup phosphor structure, remote phosphor structure has a superior luminous flux whereas its color quality is inferior to the others’. Due to this drawback, it is essential to conduct experiments to find the solution for the improvement of the color quality of WLEDs using remote phosphor structure. In this study, a dual-layer remote phosphor structure that is capable of enhancing the Color Rendering Index (CRI) and Color Quality Scale (CQS) for WLEDs was proposed. Three kinds of WLEDs with the similar structures but different color temperatures varying at 5600 K, 7000 K, and 8500 K are used in this article. The mission of this paper is to place a yellow-green emitting SrBaSiO4:Eu2+ phosphor layer or a red-emitting SrwFxByOz:Eu2+,Sm2+ phosphor layer on the YAG:Ce3+ phosphor layer and then select the most appropriate value of SrwFxByOz:Eu2+,Sm2+ concentration to get the greatest color quality. Experimental results were exactly as expected since SrwFxByOz:Eu2+,Sm2+ really succeeded in increasing CRI and CQS. Specifically, the larger the SrwFxByOz:Eu2+,Sm2+ concentration, the higher the CRI and CQS, resulting from the increase of the red light component in WLEDs. Meanwhile, the quality degree of luminous flux depends tightly on the SrBaSiO4:Eu2+ phosphor layer. However, if the SrwFxByOz:Eu2+,Sm2+ and SrBaSiO4:Eu2+ concentration exceeds, the luminous flux and color quality will have a tendency to drop off thanks to the theory of Mie scattering and the Lambert-Beer law. The result of this paper is a valuable reference in the production of high-quality WLEDs.
Highlights
Nowadays, as the demand for lighting is increasing and complex, the traditional light sources become obsolete and need to be replaced
This concept seems to be rather familiar, it cannot be denied that the structure of LEDs and the arrangement of phosphor layers play an essential role in determining the luminous efficiency, especially the color rendering index
Another paper showed that an inverted cone lens encapsulant and a surrounding ring remote phosphor layer can redirect the light from the LED chip to the surface of the LED and reduce the loss caused by internal reflection inside LED
Summary
As the demand for lighting is increasing and complex, the traditional light sources become obsolete and need to be replaced. Combining the blue light from converse red phosphor with the yellow light from LED chip is considered as the optimal method for the white light generation [4] and [5] This concept seems to be rather familiar, it cannot be denied that the structure of LEDs and the arrangement of phosphor layers play an essential role in determining the luminous efficiency, especially the color rendering index. When the distance between the phosphor and the LED chips is large enough, the backscattering and light circulation inside LED can be limited [9] and [10] This approach is an optimal solution to control the temperature of LED as well as enhancing the luminous efficiency and the LEDs’ color quality. The selection of suitable phosphor concentration becomes essential for the maintenance of photosensitivity of WLEDs
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