This study presents a novel remote phosphor design involving a concentric ring remote phosphor layer in which green and red phosphors are separated. The green and red phosphor rings were separately illuminated by blue light emitted from the light-emitting diode (LED), causing low reabsorption in phosphor-converted LEDs (pcLEDs) using green and red phosphors. The experimental results revealed that the pcLEDs with green and red phosphors showed high color rendering, indicating that the LEDs are suitable for certain medical applications and architectural lighting. Moreover, for given green/red phosphor ratio and weights of the green and red phosphors, the output power and luminous flux of the pcLED with a concentric ring remote phosphor layer were greater than those of the pcLED with a mixed remote phosphor layer. The reduction in the reabsorption of green emission by red phosphor in pcLED with a concentric ring remote phosphor layer was responsible for the high luminous flux and indicated a high correlated color temperature of pcLED.

Because of advantages such as long lifetime, low power consumption, and no mercury containing, LEDs are widely used in a variety of general-purpose illumination applications. There are two different approaches for generating white light with LEDs. The first one is the combination of phosphors excited by blue or UV LED emission, the other one is mixture of multi-color LEDs Without the power loss in the down conversion process of the white LED using phosphors, a higher efficiency and flexible option can be done with the mixture of multi-color LEDs. Questions arise on how the spectra of the mixture of colored LED designed are for good color rendering performance, more output lumens and better luminous efficiency. A lot of papers discuss the different spectrum combinations of multicolored LEDs which yield light with maximum efficacy, luminous flux and CRI, at the desired corrected color temperature, but most of them use the spectral power distribution of a model LED to calculate the luminous efficacy, luminous flux and CRI, and get the best combination as request. But as most people know, the spectral power distribution of a real LED will vary with ambient temperature, forward current and effect of aging, so simulation of the luminous efficacy, luminous flux and CRI will get some problems in practical. On the other hand, the finding of a better luminous efficacy of the mixture of colored LED can provide the best suggestion when the LED manufacturers try to select commercial LED chips to manufacture colored LED light sources. We setup a system with integrating sphere, spectrometer and four independent PC controlled powermeters, which can get the data of luminous flux, CRI and luminous efficiency of light sources automatically with different input power. Using the database from the system and simulations, we can analyze the optical and color characteristics of the mixture of colored LED light source, even the RGB LED (red, green and blue chips in one package). Then the selection of the combination of the LED chips for the mixture of colored LED light source, for generating more luminous flux, better color rendering index and luminous efficiency should be good.

Because of the predicted shortage of fossil fuels in the future, public interest in utilizing solar energy for photovoltaic (PV) electricity has exponentially increased in recent years. In particular, interest in the building integration of PVs is growing worldwide, and the use of building-integrated PVs (BIPVs) is one of the fastest growing segments of the PV industry. Luminescent solar concentrators (LSCs) are one of the possible approaches for BIPVs. However, the high cost and poor stability of the dyes or quantum dots used in conventional LSCs prevent the widespread adoption of electricity generation through the LSC-based solar energy. Therefore, inorganic phosphors with long lifetime and photostability under ultraviolet (UV) excitation and moisture are favorable luminescent materials for LSCs. In this paper, thin-film LSCs using commercial inorganic phosphors are proposed. The thin-film LSCs with different inorganic phosphors were examined. The phosphor concentration and relative position of the thin phosphor layer were investigated to determine the suitable structure of a thin-film LSC. This paper aimed to achieve an understanding of thin-film LSCs by using inorganic phosphors and to provide useful guidelines for future commercialization.

The quality assessment and reliability improvement of high-power light-emitting diodes (LEDs), which are used in lighting applications, are important. Conventional lifetime testing for LEDs lasts approximately 6000 h. Accelerated life testing (ALT) to quickly assess LED quality and faults is essential for the mass production of LEDs. This paper conducted a systematic nondestructive fault analysis for the ALT of LEDs to effectively detect defect growth. A nondestructive z-scan analysis revealed the defects across the LED cross section (top-bottom); these defects were consistent with the results of destructive focused ion beam analysis. The results showed that parasitic series resistance degrades LED performance and that it ranges from 1.5 to $10.7 Ω$ under an aging current of 1 A applied for less than 50 h.

A phosphor-converted light emitting diode with curved remote phosphor layer was obtained in this study. By changing the geometry of the flat remote phosphor layer in a conventional remote phosphor structure, the package extraction efficiency and luminous efficacy of the curved remote phosphor structure was improved by reducing the total internal reflection at the interface of the air and phosphor layer. Ray tracing simulations were performed to analyze the package extraction efficiency of the curved remote phosphor structure. Experimental results showed that the convex remote phosphor structure had high luminous efficacy with high color uniformity. The convex remote phosphor structure would be a suitable structure if the remote phosphor structure is used in lighting applications.

In this study, an improved scattered photon extraction (SPE) package structure with a reflection plate over the remote phosphor layer is presented. The important factors for the remote phosphor layer in the conventional and improved SPE package structures, including the phosphor layer thickness and phosphor concentration, are also studied. The simulation results show that the yellow–blue ratio (YBR) of the conventional and improved SPE package structure increases with the phosphor concentration when the phosphor layer is thin and that the YBR is saturated when the layer is thick. The experimental results show that for both conventional and improved SPE package structure, the correlated color temperature (CCT) decreases as the phosphor concentration increases. However, the YBR of the improved SPE package structure is higher than that of the conventional SPE package structure for a given phosphor layer thickness and phosphor concentration. That is, in the conventional SPE package structure, it is necessary to increase the phosphor concentration and then increase the absorption of blue light to obtain more yellow light. Hence, for the improved SPE package structure, less phosphor is required in the phosphor layer for achieving the chosen CCT.