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Phosphor conversion for WLEDs: YBO3: Ce3+, Tb3+ and its effects on the luminous intensity and chromatic properties of dual-layer WLED model

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My L. T. T. , Thai N. L. , Bui T. M. , Lee H.-Y. , Anh N. D. Q.

tom Vol. 40, No. 4

105--113

Yttrium borate phosphor co-doping Ce3+, Tb3+ions (YBO3: Ce3+, Tb3+) is fabricated using solid state reaction, and then its luminescence is investigated through the computational energy transfer process. Under excited near-UV light, this YBO3: Ce3+, Tb3+ phosphor exhibits strong absorption with broad and sharp emission bands due to the 4f – 5d and 5d – 4f transitions of Ce3+ ions and the 4f – 4f transition of Tb3+ ions, respectively. The phosphor’s emission chromaticity could be tunable by adjusting the concentration of doping ions. With 15% Tb3+ and 3% Ce3+ in the composition, the phosphor can gain maximum 76.7% external quantum efficacy. The phosphor is proposed for utilization in the phosphor package of white light-emitting diodes (WLEDs) to enhance their lighting performances. The findings point out that by modifying YBO3: Ce3+, Tb3+ concentration (5% – 10%), improvements in luminous intensities, color consistency, and color rendering indices can be observed. The higher concentration (10%) of YBO3: Ce3+, Tb3+ is more advantageous to the luminous flux and chromatic uniformity in cases of 4000 K and 5000 K WLEDs, while lower (5%) concentration greatly benefits those properties in the case of 3000 K WLED. Regardless of CCTs, the WLEDs show a reduction in chromatic reproduction efficiency with the increasing concentration of YBO3: Ce3+, Tb3+ . Hence, this green phosphor could be a good material for high-luminescence WLED, yet the modification of phosphor concentration is advisable if the simultaneous good chromaticity is desired.

Triple-layer remote phosphor structure: a novel option for the enhancement of WLEDs’ color quality and luminous flux

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Thi M. H. N. , That P. T. , Anh N. D. Q. , Thanh T. T.

tom Vol. 38, No. 4

654--660

The remote phosphor as a lighting structure has outstanding luminous efficiency compared to other options, such as conformal or in-cup. However, the lack of uniformity in distributed color has prevented remote phosphor from wider development. The answer to the chromatic performance enhancement that has been suggested by numerous researchers is the multi-layer configuration with two or three different types of chromatic phosphor. The research purpose is to select the best configuration for multi-chip white LEDs (WLEDs) to achieve optimal results in color quality scale (CQS), color rendering index (CRI), light output and color homogeneity. WLEDs mentioned in this paper have two distinct color temperatures, 6600 K and 7700 K. Experimental results show that the remote phosphor structure with three phosphor layers is superior in terms of color rendering, chromatic performance, and emitted light. The deviation of correlated color measured in this structure is also low, which means that the color uniformity is greatly enhanced in this multi-layer lighting structure. This result can be demonstrated by analyzing the scattering characteristics of the phosphoric layers using the Mie theory. The research findings have proven the effectiveness of the multi-phosphor configuration and can serve as a guideline to fabricate WLEDs with better performance.