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

100%

Huu P. D. , Thai N. L. , Le P. X.

tom Vol. 40, No. 2

159--169

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.

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

100%

Le P. X. , Ho S. D. , Anh N. D. Q. , Lee H.-Y.

2021

tom Vol. 39, No. 4

458--466

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.

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

88%

Le P. X. , Trang T. T. , Anh N. D. Q. , Lee H.-Y. , Tho L. V.

tom Vol. 40, No. 1

1--8

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.