Xinrui Ding

Light Extraction Improvement for LED COB Devices by Introducing a Patterned Leadframe Substrate Configuration

We propose a patterned leadframe substrate (PLS) configuration for light-emitting diode chip-on-board devices (LED COBs) with regular triangular structures on it. The mechanism of this method is analyzed through ray dynamics, which indicate that the light-propagating regimes are considerably different as the structure inclination angle α changes. For typical encapsulant materials (refractive index=1.41), the optimal α is 22.5°~45°. Then the performance of LED COB devices with PLS configurations are verified through 3-D Monte Carlo ray-tracing simulations as well as experimental measurements. Results show that the light-extraction efficiency is significantly improved. A simulated enhancement of 42% and a measured enhancement of 41.07% are observed. These results are in good consistency with the ray dynamic analysis, confirming our predictions about PLS methods. Furthermore, we find that such an LED COB configuration also provides a way to change the angular distribution of intensity from half-peak side angle 101.84° to 141.80°. The findings of our work represent a new concept for LED COB packaging design of great practicality in building lighting systems.

Improving LED CCT uniformity using micropatterned films optimized by combining ray tracing and FDTD methods

Although the light-emitting diode (LED) has revolutionized lighting, the non-uniformity of its correlated color temperature (CCT) still remains a major concern. In this context, to improve the light distribution performance of remote phosphor LED lamps, we employ a micropatterned array (MPA) optical film fabricated using a low-cost molding process. The parameters of the MPA, including different installation configurations, positioning, and diameters, are optimized by combining the finite-difference time-domain and ray-tracing methods. Results show that the sample with the upward-facing convex-cone MPA film that has a diameter of half of that of the remote phosphor glass, and is tightly affixed to the inward surface of the remote phosphor glass renders a superior light distribution performance. When compared with the case in which no MPA film is used, the deviation of the CCT distribution decreases from 1033 K to 223 K, and the corresponding output power of the sample is an acceptable level of 85.6%. We perform experiments to verify our simulation results, and the two sets of results exhibit a close agreement. We believe that our approach can be used to optimize MPA films for various lighting applications.

A Detailed Study on Phosphor-Converted Light-Emitting Diodes With Multi-Phosphor Configuration Using the Finite-Difference Time-Domain and Ray-Tracing Methods

Although the optical simulations have been widely adopted to study phosphor-converted light-emitting diodes (pcLEDs), to the best of our knowledge, there is no study that investigates the pcLED model considering the effect of phosphor particles with irregular shapes. In order to explore this topic, we employ the finite-difference time-domain method to characterize the phosphor-converted element (PCE) model. Furthermore, the PCE-based pcLED with YAG:Ce and nitride phosphors is investigated by the ray-tracing method. The results show that the rod-shaped nitride phosphor can scatter incident light to larger angles compared with the spherical YAG:Ce phosphor of the same size. In turn, their different scattering and absorption characterizations cause that the mixing concentration of the phosphors has a significant effect on the correlative color temperature and light output power of the pcLED.

CCT-tunable LED device with excellent ACU by using micro-structure array film.

We apply a microstructure array (MSA) film to improve the angular color uniformity (ACU) of a correlated-color-temperature-tunable LED (CCT-tunable LED) with tunable CCT ranging from 2700 to 6500 K. The effects of the MSA film area and the height between the film and LED are investigated and optimized. The resulting ACU is greatly improved for all CCT ranges with little luminous flux loss. For a typical CCT range of 3000-4000 K, with a full-covering MSA film and height H = 5 mm, the CCT deviation is significantly reduced from 1090 K to 218 K, with only 1.8% luminous flux loss.

Color uniformity enhancement for COB WLEDs using a remote phosphor film with two freeform surfaces

The color uniformity (CU) of chip-on-board (COB) white light emitting diodes (WLEDs) has been improved by using remote phosphor films with two freeform surfaces (TFS-RPFs). The finite-difference time-domain (FDTD), Monte Carlo ray-tracing, and color-thickness feedback (CTFB) methods were used to design the TFS-RPFs: the blue light distribution of COB WLEDs is greatly affected by the angular thickness distribution of TFS-RPFs, and a high CU can be achieved iteratively. The directional inconsistency of incident and emergent blue light, scattering effect of TFS-RPFs, and illumination characteristics of the COB source were also investigated. COB WLEDs containing optimized TFS-RPFs achieved high CU with a decrease of 26.2% in maximum CCT deviation; thus, TFS-RPFs can improve the CU of COB WLEDs.

Efficient synthesis of highly fluorescent carbon dots by microreactor method and their application in Fe3 + ion detection

Rapidly obtaining strong photoluminescence (PL) of carbon dots with high stability is crucial in all practical applications of carbon dots, such as cell imaging and biological detection. In this study, we proposed a rapid, continuous carbon dots synthesis technique by using a microreactor method. By taking advantage of the microreactor, we were able to rapidly synthesized CDs at a large scale in less than 5min, and a high quantum yield of 60.1% was achieved. This method is faster and more efficient than most of the previously reported methods. To explore the relationship between the microreactor structure and CDs PL properties, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were carried out. The results show the surface functional groups and element contents influence the PL emission. Subsequent ion detection experiments indicated that CDs are very suitable for use as nanoprobes for Fe3+ ion detection, and the lowest detection limit for Fe3+ is 0.239μM, which is superior to many other research studies. This rapid and simple synthesis method will not only aid the development of the quantum dots industrialization but also provide a powerful and portable tool for the rapid and continuous online synthesis of quantum dots supporting their application in cell imaging and safety detection.

ACU Optimization of pcLEDs by Combining the Pulsed Spray and Feedback Method

In this paper, the pulse-sprayed (PS) phosphor coating technique and feedback method were combined to optimize the angular color uniformity of remote phosphor-converted light-emitting diodes (pcLEDs). The geometry of the phosphor-converted element (PCE) was controlled by the PS technique and the curvature of the phosphor bearing surface. Meanwhile, the yellow and blue light irradiance distributions are as the feedback function to optimize the mass distribution of the PS PCE during the feedback iteration process. With the method proposed herein, the correlative color temperature of the optimized remote pcLED ranges from 5192 to 5263 K with a maximum deviation of only 71 K.

Energy feedback freeform lenses for uniform illumination of extended light source LEDs

Using freeform lenses to construct uniform illumination systems is important in light-emitting diode (LED) devices. In this paper, the energy feedback design is used for freeform lens (EFFL) constructions by solving a set of partial differential equations that describe the mapping relationships between the source and the illumination pattern. The simulation results show that the method can overcome the illumination deviation caused by the extended light source (ELS) problem. Furthermore, a uniformity of 95.6% is obtained for chip-on-board (COB) compact LED devices. As such, prototype LEDs manufactured with the proposed freeform lenses demonstrate significant improvements in luminous efficiency and emission uniformity.

Full spectral optical modeling of quantum-dot-converted elements for light-emitting diodes considering reabsorption and reemission effect

Quantum dots (QDs) have attracted significant attention in light-emitting diode (LED) illumination and display applications, owing to their high quantum yield and unique spectral properties. However, an effective optical model of quantum-dot-converted elements (QDCEs) for (LEDs) that entirely considers the reabsorption and reemission effect is lacking. This suppresses the design of QDCE structures and further investigation of light-extraction/conversion mechanisms in QDCEs. In this paper, we proposed a full spectral optical modeling method for QDCEs packaged in LEDs, entirely considering the reabsorption and reemission effect, and its results are compared with traditional models without reabsorption or reemission. The comparisons indicate that the QDCE absorption loss of QD emission light is a major factor decreasing the radiant efficacy of LEDs, which should be considered when designing QDCE structures. According to the measurements of fabricated LEDs, only calculation results that entirely consider reabsorption and reemission show good agreement with experimental radiant efficacy, spectra, and peak wavelength at the same down-conversion efficiency. Consequently, it is highly expected that QDCE will be modeled considering the reabsorption and reemission events. This study provides a simple and effective modeling method for QDCEs, which shows great potential for their structure designs and fundamental investigations.

Study on Scattering and Absorption Properties of Quantum-Dot-Converted Elements for Light-Emitting Diodes Using Finite-Difference Time-Domain Method

CdSe/ZnS quantum-dot-converted elements (QDCEs) are good candidates for substituting rare-earth phosphor-converted elements (PCEs) in white light-emitting diodes (LEDs); however, studies on their scattering and absorption properties are scarce, suppressing further increment in the optical and thermal performance of quantum-dot-converted LEDs. Therefore, we introduce the finite-difference time-domain (FDTD) method to achieve the critical optical parameters of QDCEs when used in white LEDs; their scattering cross-section (coefficient), absorption cross-section (coefficient), and scattering phase distributions are presented and compared with those of traditional YAG phosphor-converted elements (PCEs) at varying particle size and concentration. At a commonly used concentration (<50 mg/cm3), QDCEs exhibit stronger absorption (tens of millimeters, even for green-to-red-wavelength light) and weaker scattering (<1 mm−1) compared to PCEs; the reabsorption, total internal reflection, angular uniformity, and thermal quenching would be more significant concerns for QDCEs. Therefore, the unique scattering and absorption properties of QDCEs should be considered when used in white LEDs. Furthermore, knowledge of these important optical parameters is helpful for beginning a theoretical study on quantum-dot-converted LEDs according to the ray tracing method.