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1

Studying CdS:In green phosphor's impacts on white-light emitting diode with higher luminous flux

Huu Phuc Dang, Thai Nguyen Le, Le Phan Xuan

Materials Science Poland

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2022

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Vol. 40, No. 2

159--169

EN

A lumen efficiency (LE) simulation model with the Monte Carlo method is introduced to the white-light-emitting diode devices that utilize the red LED (light-emitting diode) dyes instead of red-emitting phosphors (R-WLEDs). By simulating this model, the desirable spectrum-related indices and photometric efficiencies, which are adequate for superior chromatic consistency (or Rf > 97), can be accomplished for R-WLEDs under the correlated color temperature (CCT) range of 5000–8000 K. The structure of the R-LED has LEDs in red and blue colors (650 nm and 448 nm) combined with phosphors possessing yellow and green emissions (586 nm and 507 nm). In comparison with pc-WLEDs (WLEDs operating with conversion phosphors) and QD-WLEDs (WLED devices with quantum dots), pc/R-WLED devices could present its outperformance to the others and become a promising way to achieve remarkable chromatic generation, particularly under the condition of small color temperature limit, and act as a substitute for the pc-WLED devices.

2

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.

3

Comparison between SEPs of CaCO3 and TiO2 in phosphor layer for better color uniformity and stable luminous flux of WLEDs with 7,000 K

Le Phan Xuan, Trang Tran Thanh, Anh Nguyen Doan Quoc, Lee Hsiao-Yi, Tho Le Van

Materials Science Poland

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2022

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Vol. 40, No. 1

1--8

EN

CaCO3 and TiO2 are proposed in this study as particles for scattering enhancement (SEPs) of phosphor-converted white light-emitting diodes (pc-WLEDs). The use of these two SEPs for scattering improvement enables boosting of the color homogeneity of the WLED devices. Each SEP is mixed with YAG:Ce3+ and silicone composition to examine their optical influences and performances on the high-power WLED packages with 7,000 K color temperature (CT). Miescattering theory is applied to calculate and investigate the scattering elements - scattering coefficients, anisotropic scattering, the reduced scattering, and scattering amplitudes - at the wavelengths of 450 nm and 550 nm. The results exhibit that TiO2and CaCO3 considerably promote higher color uniformity and color-deviated reduction, respectively. The obtained results could be primarily attributed to the significant improvement in the scattering properties of the structure. Additionally, the effects of the presented scattering enhancement on luminous efficiency are displayed. The reduction in lumen output is observed to have a close connection with the concentration and particle size of TiO2and CaCO3, which means that control must be exercised over these factors when utilizing these SEPs for WLED fabrication.

4

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.

5

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.

6

The impacts of Ba2Li2Si2O7:Sn2+,Mn2+ and CaMgSi2O6:Eu2+,Mn2+ particles on the optical properties of remote phosphor LED

Chen Ming-Jui, Loan Nguyen Thi Phuong, Tho Le Van, Bui Thuc Minh, Le Phan Xuan, Anh Nguyen Doan Quoc, Liao Hsing-Yuan, Chang Jui-Chen, Lee Hsiao-Yi

Materials Science Poland

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2020

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Vol. 38, No. 1

197--205

EN

As implied in the title, the triple-layer remote phosphor (TRP), constructed with the yellow YAG:Ce3+ layer at the bottom, the red CaMgSi2O6:Eu2+,Mn2+ phosphor layer on the top, and the green Ba2Li2Si2O7:Sn2+,Mn2+ phosphor layer between these two layers, is suggested in this paper to improve the color and luminescence of white LEDs (WLEDs). In order to control the red light for the purpose of increasing the color rendering index (CRI), it is suggested that the red CaMgSi2O6:Eu2+,Mn2+ phosphor should be applied in the TRP structure. Simultaneously, the structure uses the green Ba2Li2Si2O7:Sn2+,Mn2+ phosphor layer to control the green light, which increases the luminous efficacy (LE) of WLEDs. In addition, when the concentration of these two phosphors increases, the yellow YAG: Ce3+ concentration must be reduced to keep the average correlated color temperatures (ACCTs) stable at 6000 K to 8500 K. Besides, appropriate adjusting of CRI, LE, and color quality scale (CQS) is also analyzed by modifying the concentration of the green phosphor and red phosphor. The results show that the CRI can get better values if CaMgSi2O6:Eu2+,Mn2+ concentration is higher. In contrast, the CRI decreases dramatically when the concentration of Ba2Li2Si2O7:Sn2+,Mn2+ increases. Meanwhile, CQS can be significantly increased in the range of 10 % to 14 % CaMgSi2O6:Eu2+,Mn2+, regardless of the concentration of Ba2Li2Si2O7:Sn2+,Mn2+. In particular, along with the improvement of CRI and CQS, LE can also be increased by more than 40 % by reducing the scattered light and adding the green light. Obtained results are a valuable reference for manufacturers for improving WLEDs color and luminescence quality to produce a broader range of WLEDs with better quality fulfilling social needs.

7

Enhancing color quality of WLEDs with dual-layer remote phosphor geometry

That Phung Ton, Loan Nguyen Thi Phuong, Tho Le Van, Anh Nguyen Doan Quoc, Liao Hsing-Yuan, Luo Guo-Feng, Lee Hsiao-Yi

Materials Science Poland

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2020

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Vol. 38, No. 4

667--674

EN

Usually, remote phosphor structures are beneficial in terms of flux but unfavorable in terms of color quality compared to conformal phosphor or in-cup phosphor packages. To eliminate this disadvantage, many studies have focused on increasing the chromatic quality of the remote phosphor configuration, which requires great efforts in improving two parameters of color: color rendering index (CRI) and color quality scale (CQS). CRI is known as the most useful quantitative method used to measure the ability of a light source to reproduce the colors of illuminated objects faithfully and naturally. Similarly, CQS is also a method of lighting quality determination and analysis, especially used as an alternative to the unsaturated CRI colors. In this paper, we proposed dual-layer remote phosphor structure as a novel method of CRI and CQS enhancement to improve WLEDs’ color quality. Five alike WLEDs but having different color temperatures in the range of 5600 K to 8500 K were applied in this study. The idea behind the study is to place a red phosphor layer SrwFxByOz:Eu2+,Sm2+ on the yellow phosphor layer YAG:Ce3+ and then determining an appropriate concentration of SrwFxByOz:Eu2+,Sm2+ added to achieve the highest color quality. The results point out that SrwFxByOz:Eu2+,Sm2+ brings great benefits to the improvement of CRI and CQS parameters. Specifically, the higher the SrwFxByOz:Eu2+,Sm2+ concentration results in the greater CRI and CQS, owning to the enriched red light components in the WLEDs. However, the flux has a tendency of dropping when SrwFxByOz:Eu2+,Sm2+ concentration rises excessively. This has been proved by using the Mie-scattering theory and the Lambert-Beer law. The results of this article are essential references for manufacturing WLEDs with higher chromatic quality.

8

Building superior lighting properties for WLEDs utilizing two-layered remote phosphor configurations

Anh Nguyen Doan Quoc, Ngoc Hoang Van

Materials Science Poland

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2020

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Vol. 38, No. 3

493--501

EN

The remote phosphor structure produces higher luminous flux but delivers poorer color quality than the conformal or in-cup phosphor structure. To eliminate this weakness, researchers have attempted to improve the chromatic properties of remote phosphor package. This study tends to enhance lighting features for WLEDs including color quality and luminous flux in general or color rendering index (CRI) and color quality scale (CQS) in particular by applying dual-layer remote phosphor structure. In the simulation section, we utilize two identical LEDs that only differ in correlated color temperature values which are 6600 K and 7700 K. The study offers an idea of placing a yellow-green phosphor layer SrBaSiO4:Eu2+ or a red phosphor layer SrwFxByOz:Eu2+,Sm2+ on the yellow phosphor layer YAG:Ce3+ and then modifying the concentrations of SrwFxByOz:Eu2+,Sm2+ and SrBaSiO4:Eu2+ to the suitable values to improve the color quality and lumen output of WLEDs. The results show that red phosphor layer SrwFxByOz:Eu2+,Sm2+ has a significant influence on CRI and CQS improvement. Particularly, the increase of SrwFxByOz:Eu2+,Sm2+ concentration leads to increased CRI and CQS because the red light component increases in WLEDs. On the other hand, the green phosphor layer SrBaSiO4:Eu2+ only brings benefit to the luminous flux. However, the WLEDs’ luminous flux and color quality drop sharply, when SrwFxByOz:Eu2+,Sm2+ and SrBaSiO4:Eu2+ concentrations rise extremely, which is verified based on the Mie-scattering theory and the Lambert-Beer law. In short, the article provides general knowledge and primary information for the production of higher-quality WLEDs.

9

Improving color uniformity and color rending index of remote-phosphor packaging white LEDs by co-doping SiO2 and Sr2Si5N8:Eu2+ particles

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

Materials Science Poland

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2018

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Vol. 36, No. 3

370--374

EN

Based on some advantageous properties, such as fast response time, environment friendliness, small size, long lifetime, and high efficiency, white LEDs are increasingly used in common illumination applications. In this research, by co-doping of redemitting Sr2Si5N8:Eu2+ phosphor and adding SiO2 particles to yellow-emitting YAG:Ce phosphor compounds, a new approach for improving color uniformity and color rending index of remote-phosphor structure white LEDs is proposed and demonstrated. The obtained results clearly indicate that the color rendering index (CRI) and color uniformity (DCCT) significantly depend on Sr2Si5N8:Eu2+ concentration. The results provide a potential practical solution for manufacturing remote-phosphor white LEDs (RP-WLEDs) in the near future.

10

Green-emitting CaF2:Ce3+,Tb3+ phosphor: selection for improving luminous flux and color quality of conformal geometry white LED lamps

Tin P. T., Minh T. H. Q., Nhan N. H. K., Lee H.-Y., Trang T. T.

Materials Science Poland

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2018

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Vol. 36, No. 4

563--569

EN

In the last decades, new solutions for improving lighting properties of white LED lamps (WLEDs) have been the main research direction in optoelectronics. In this paper, a modern approach for enhancing luminous flux and color quality of white LED lamps was presented. By mixing green-emitting CaF2:Ce3+,Tb3+ phosphor with yellow-emitting YAG:Ce phosphor compound, the luminous flux and color quality of white LED lamps with conformal phosphor geometry (CPG) increased significantly. From the obtained results it follows that, the luminous flux increased more than 1.5 times, and the correlated color temperature deviation decreased more than 4 times in comparison with the non-green-emitting CaF2:Ce3+,Tb3+ phosphor. The presented research shows that the green-emitting CaF2:Ce3+,Tb3+ phosphor could become a good candidate for enhancing luminous flux and color quality of white LED lamps.