SiO2 particles and red-emitting CaMgSi2O6:Eu2+,Mn2+ phosphor have been added into a yellow phosphor compound YAG:Ce3+ to enhance the optical efficiency of white light LEDs whose average correlated color temperature (CCT) is in the range of 5600 K ÷ 8500 K. It was observed that altering CaMgSi2O6:Eu2+,Mn2+ concentration from 2 % to 30 % while maintaining 5 % of the SiO2 strongly influenced the color rendering index (CRI), color quality scale (CQS), and lumen efficiency of the compound. Besides, through the application of Monte Carlo simulation and Mie-scattering theory, it was possible to improve the optical properties by CaMgSi2O6:Eu2+,Mn2+ and SiO2 addition. The results provided a practical approach to achieve higher luminous efficiency and better color uniformity in remote-phosphor white LEDs (RP-WLEDs).

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.

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.

The results obtained from EHM project showed that the water environmental quality of studied area has been put in the ranks "B" and "C", it corresponds with the ecological health categories from average to bad level, the worst level was observed right at discharged throat of Nhieu Loc-Thi Nghe channel, where the water of channel has not been treated completely and having been discharged directly into Sai Gon river. The results of the classifying for water environmental quality derived from ecological health ranking method provided the understandable informations of water pollution levels at defined sites and time. It is serves as a basic for the authorities as well as the citizens to understand the water quality sources and what kinds and whether the water safe and suitable for intentional uses. This research was the first contribution to reality and theory in the field of ecological quality supervising resrearch for the Sai Gon river in particular and for other rivers and canals of Ho Chi Minh city in future.

The effects of red light-emitting phosphor CaMgSi2O6:Eu2+,Mn2+ on the optical properties of single-layer remote phosphor structure (SRPS) and dual-layer remote phosphor structure (DRPS) are the focus of this study. The differences in color quality and luminous flux (LF) of white light-emitting diodes (WLEDs) between these two structures are also revealed and demonstrated based on the Mie theory. SRPS consists of one mixed phosphor layer betweenCaMgSi2O6:Eu2+,Mn2+ andYAG:Ce3+particles, while DRPS includes two separated layers: red phosphor layer and yellow phosphor layer. In this work, 5% SiO2 is added into the phosphor layers to increase scattering abilities. Discrepancies in structures greatly affect the optical characteristics of WLEDs. The results showed that the color rendering index (CRI) increased with the concentration in both structures with nearly equal values. Meanwhile, color quality scale (CQS) of DPRS is 74 at ACCTs ranging from 5600K to 8500K, higher than CQS of SRPS which is only 71 at 8500K. In addition, the luminous flux of DRPS is significantly higher than SRPS at 2% -14% of CaMgSi2O6:Eu2+,Mn2+. In summary, DRPS is better for color quality and lumen outputin comparison to SRPS and adding the right amount of red phosphor can enhance CQS and LF.