Effect of the green-emitting CaF2:Ce3+,Tb3+ phosphor particles’ size on color rendering index and color quality scale of the in-cup packaging multichip white LEDs

In this paper, we investigate the effect of the green-emitting CaF2:Ce (3+), Tb (3+) phosphor particle's size on the color rendering index (CRI) and the color quality scale (CQS) of the in-cup packaging multichip white LEDs (MCW-LEDs). For this purpose, 7000K and 8500K in-cup packaging MCW-LEDs is simulated by the commercial software Light Tools. Moreover, scattering process in the phosphor layers is investigated by using Mie Theory with Mat Lab software. Finally, the research results show that the green-emitting CaF2: Ce (3+), Tb (3+) phosphor's size crucially influences on the CRI and CQS. From that point of view, CaF2: Ce (3+), Tb (3+) can be proposed as a potential practical direction for manufacturing the in-cup packaging phosphor WLEDs.Web of Science13235134

Hybrid remote quantum dot/powder phosphor designs for display backlights

Quantum dots are ideally suited for color conversion in light emitting diodes owing to their spectral tunability, high conversion efficiency and narrow emission bands. These properties are particularly important for display backlights; the highly saturated colors generated by quantum dots justify their higher production cost. Here, we demonstrate the benefits of a hybrid remote phosphor approach that combines a green-emitting europium-doped phosphor with red-emitting CdSe/CdS core/shell quantum dots. Different stacking geometries, including mixed and separate layers of both materials, are studied at the macroscopic and microscopic levels to identify the configuration that achieves maximum device efficiency while minimizing material usage. The influence of reabsorption, optical outcoupling and refractive index-matching between the layers is evaluated in detail with respect to device efficiency and cost. From the findings of this study, general guidelines are derived to optimize both the cost and efficiency of CdSe/CdS and other (potentially cadmium-free) quantum dot systems. When reabsorption of the green and/or red emission is significant compared to the absorption strength for the blue emission of the pumping light emitting diode, the hybrid remote phosphor approach becomes beneficial

Improving color quality and luminous flux of white LED utilizing triple-layer remote phosphor structure

In this manuscript, we presented a research that enhance the performance of WLED using the multi-phosphor configuration. The phosphor layers in the research are separated from each other to achieved better luminous efficiency, however, it makes controlling color light quality more complex. Another issue is finding out the whether two layers of phosphor or three layers of phosphor is better in improving color quality. The research addressed this issue by analyzing the optical aspects of the respective WLEDs that employ these structure. The studied aspects are quality indicators such as luminous efficacy (LE), and color uniformity, color rendering index (CRI), color quality scale (CQS). The results of the experiments in this research, which come from the employment of WLEDs with 2 color temperatures 5600 K and 8500, suggest that WLED with three phosphor layers is better in CRI, CQS, LE. This type of phosphor structure also limits the color deviation significantly, thus, improves the color uniformity. This results is verifies with Mie theory, therefore, can be applied as reference or guideline for production of better WLED

Effect of selected luminescent layers on CCT, CRI, and response times

Phosphors have been used as wavelength converters in illumination for many years. When it is excited with blue light, the frequently used yttrium aluminium garnet doped with cerium (YAG:Ce) phosphor converts a part of blue light to a wideband yellow light, resulting in the generated light having a white color. By combining an appropriate concentration of the YAG:Ce phosphor and blue excitant light, white light of a desired correlated color temperature (CCT) can be obtained. However, this type of illumination has a lower color rendering index value (CRI). In an attempt to improve the CRI value, we mixed the YAG:Ce phosphor with europium-doped calcium sulfide phosphor (CaS:Eu), which resulted in a considerably increased CRI value. This article examines an experiment with luminescent layers consisting of a mixture of selected phosphors and polydimethylsiloxane (PDMS). Different thicknesses in these layers were achieved by changing the speed of rotation during their accumulation onto laboratory glass using the method of spin coating. The spectral characteristics of these luminescent layers as they were excited with blue light emitting diode (LED) and laser diode (LD) were then determined. A suitable combination of the YAG:Ce phosphor with a phosphor containing europium, as it was excited with a blue LED, yielded a source of white light with a CRI value of greater than 85. The response time in the tested luminescent layers to a rectangular excitant impulse (generated by a signal generator and transmitted by LD) was also measured in order to examine their potential use in visible light communications (VLC).Web of Science1213art. no. 209

Using flat phosphor layer in dual-layer remote phosphor configuration to improve luminous efficacy

The phosphor layer shape and components distances are the subjects proposed to advance the quality of WLEDs in this article. The two distances, between phosphor layers (d1) and between the phosphor layer and the LED chip (d2) in Flat dual-remote phosphor (FDRP) and Concave dual-remote phosphor (CDRP) were examined by experiments to determine their impacts on WLEDs lighting performances. The results suggest that FDRP is a better option than CDRP for lighting performance. In each respective structure, the distances influence the lighting capacity and color output whenever they fluctuate. Therefore, to effectively control and study this phenomenon, the correlated color temperature is maintained at 8500 K, and the concentration of phosphor material is altered while the distances are changing. When d1 and d2 are at the starting value of 0, the recorded lumen output and chromatic performance of lighting devices are the lowest and begin to increase as d1 and d2 expand. Bigger d1 and d2 mean bigger scattering area and better chromatic light integration, which leads to higher color quality. Detailed results present that optimal values of d1 or d2 for the highest lumen output of 1020 lm are 0.08 mm or 0.63 mm, respectively. Meanwhile the lowest color deviation is accomplished with d1=0.64 mm or d2=1.35 mm

Improving color rendering index of WLEDs with convex-dual-layer remote phosphor geometry using red-emitting CaGa2S4:Mn2+ phosphor

The white-light light-emitting diode (LED), a conventional illumination solution, usually consists of one chip and one phosphor layer, which leads to the insufficient color rendering index (CRI) in this configuration. To optimize the efficiency of WLED, a new LED package with 2 chips and one phosphor was proposed, this innovative configuration can yield more lights and achieve high CRI. Thus, this study aims at perfecting the color performance with the two chips and dual phosphor layers package with the proportions and densities of phosphor in the silicone constantly changed to find the best option. The white-light LED module is adjusted using a specialized color design model. The comparison results between the measured and the simulation from the color design model CIE 1931 color coordinates suggest that the highest discrepancy is about 0.0063 and is achieved at around 5600K correlated color temperature (CCT). This study’s results lay a firm path in customizing white-light LED modules that guarantee CRI and lumen output qualities

Acquiring higher lumen efficacy and color rendering index with green NaYF4:Er3+Yb3+ and red α-SrO·3B2O3:Sm2+ layers for designing remote phosphor LED

Lighting devices that apply diodes to create white light-emitting diodes (WLEDs) can achieve remarkable results in color quality, especially those containing quantum dots (QDs) and phosphor. The technique to create an appropriate package is providing spaces between the QDs and phosphor components which helps decrease the ratio of the reabsorption losses and keeps the QDs surface ligands constant. The research aims to perfect the constructing method of remote phosphor configuration containing quantum dots and phosphor materials that based on lighting properties and temperature feature of WLEDs. The infrared thermography is the tool to measure and analyze total emitted light and emission ranges of the device. This device is also used in temperature simulation and experimental verification. At the given mA of 60, the WLEDs structure with green QDs layer above the phosphor layer results in 996 lm luminous flux (LF), and Ra = 57 in color rendering ability. Meanwhile, luminous flux of WLEDs with red QDs-on-phosphor structure is 632, and Ra = 70. Furthermore, comparing with the green QDs-on-phosphor type, the red QDs-on-phosphor type emitted less LF. However, the red QDs-on-phosphor type can be the most effective package design to achieve color rendering ability

Improving luminous flux and color homogeneity of dual-layer phosphor sctructure

In order to clarify the main purpose of the study, we put a green phosphor layer SrBaSiO4:Eu2+ on the yellow phosphorus layer YAG:Ce3+ through using only one WLEDs structure in different color temperatures like 5600 K, 6600 K, 7700K. Then, we find the suitable SrBaSiO4:Eu2+ concentration in order that the luminous flux could get the highest value. The results show that SrBaSiO4:Eu2+ brings great benefits to increase not only optical gain but also color uniformity. Specifically, the greater the SrBaSiO4:Eu2+ concentration, the greater the output of WLEDs because of the development of green light component in WLEDs. However, only if the SrBaSiO4:Eu2+ concentration exceeds the level, a slight decrease in color rendering index (CRI) can occur, which based on Monte Carlo simulation. In addition, the results of this paper have contributed significantly to the creation of higher-powered WLEDs