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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

My Le Thi Thuy, Thai Nguyen Le, Bui Thuc Minh, Lee Hsiao-Yi, Anh Nguyen Doan Quoc

Materials Science Poland

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2022

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Vol. 40, No. 4

105--113

EN

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.

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Better color distribution uniformity and higher luminous intensity for LED by using a three-layered remote phosphor structure

Loan Nguyen Thi Phuong, Anh Nguyen Doan Quoc, Trang Nguyen Cong, Lee Hsiao-Yi

Materials Science Poland

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2022

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Vol. 40, No. 1

60--67

EN

Angular color distribution uniformity has been one of the most relevant properties in the development of white light-emitting diodes (WLEDs), since color consistency and uniformity are crucial factors in quality evaluation of a WLED. Here, particularly considering the need to overcome the poor chromaticity usually associated with WLED, we introduce a new design for the remote-phosphor package, namely a three-layered or triple-layer (TL) phosphor structure. Using three phosphor layers in packaging a WLED can result in higher color quality and luminous efficacy, compared to the double-layer (DL) configuration. In the present study, the results of using three remote phosphor layers indicate that although the structure using three layers has a lower color rendering index, the color quality scale is better than that available from the package with two layers. Additionally, the color-deviation values in the TL structure are smaller than in the dual-layer one, especially at high color temperatures (7,700 K and 8,500 K). Besides, in comparison with the DL model, the TL package increases the luminous flux by 1.4%–2%. Therefore, the TL remote phosphor structure possesses the greatest potential in enhancing the WLED quality.

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Triple-layer remote phosphor structure: A potential packaging configuration to enhance both color quality and lumen efficiency of 6,000–8,500 K WLEDs

Le Phan Xuan, Ho Sang Dang, Anh Nguyen Doan Quoc, Lee Hsiao-Yi

Materials Science Poland

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2021

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Vol. 39, No. 4

458--466

EN

To achieve further enhancement in the lighting quality of white light-emitting diodes (WLEDs), this study proposed apackaging structure with three different phosphor layers, called triple-layer remote phosphor structure. This structure can provide an overall control over the light color distribution of WLEDs. The yellow-green-emitting CaAl2O4:Mn2+ phosphor andredemitting CaMoO4:Eu3+ phosphor are used along with the original yellow-emitting YAG:Ce3+phosphor to fabricate thetriple-layer structure. The concentration of yellow-emitting YAG:Ce3+phosphor is required to be decreased as the concentrations of other phosphors increase to keep the predetermined correlated color temperatures. The color rendering index (CRI) and the color quality scale (CQS) are measured to reach a thorough color quality assessment for WLEDs. The color management can be achieved by adjusting the concentration of red-emitting CaMoO4:Eu3+ phosphor to enhance the red emission. In addition, adjustment of the concentration of yellow-green-emitting CaAl2O4:Mn2+ phosphor can result in higher luminousefficiency owing to its control over the green light components. Higher CRI is observed when CaMoO4:Eu3+ concentration increases, while an increase in CaAl2O4:Mn2+ phosphor leads to much lower CRI. The CQS – on the other hand – is remarkably high when the CaMoO4:Eu3+ concentration range is about 10wt%–14wt%, regardless of the proportion of the CaAl2O4:Mn2+ phosphor. Furthermore, 40% enhancement in luminous efficiency is also achieved since light scattering is minimized by the boosted green-light emission spectra. Manufacturers can take these findings as reference to fabricate high-quality WLED lights that fulfill all their requirements.

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Novel lighting properties of white LEDs with two-layered remote phosphor package using red-emitting α-SrO•3B2O3:Sm2+ phosphor

Minh T. H. Q., Nhan N. H. K., Anh N. D. Q., Lee H.-Y.

Materials Science Poland

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2017

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Vol. 35, No. 3

618--625

EN

This paper investigates a method for improving the lighting performance of white light-emitting diodes (WLEDs), packaged using two separating remote phosphor layers, yellow-emitting YAG:Ce phosphor layer and red-emitting α-SrO•3B2O3:Sm2+ phosphor layer. The thicknesses of these two layers are 800 μm and 200 μm, respectively. Both of them have been examined at average correlated color temperatures (CCT) of 7700 K and 8500 K. For this two-layer model, the concentration of red phosphor has been varied from 2 % to 30 % in the upper layer, while in the lower layer the yellow phosphor concentration was kept at 15 %. It was found interesting that the lighting properties, such as color rendering index (CRI) and luminous flux, are enhanced significantly, while the color uniformity is maintained at a level relatively close to the level in one-layer configuration (measured at the same correlated color temperature). Besides, the transmitted and reflected light of each phosphor layer have been revised by combining Kubelka-Munk and Mie-Lorenz theories. Through the analysis, it is demonstrated that the packaging configuration of two-layered remote phosphor that contains red-emitting α-SrO•3B2O3:Sm2+ phosphor particles provides a practical solution to general WLEDs lighting.