Zongtao Li

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.

Microstructure and hydrogen absorption properties of nano-phase composite prepared by mechanical alloying of MmNi5−x(CoAlMn)x and Mg

Abstract In this work high energy ball milling was used to prepare composite hydrogen storage alloy in the MmNi 5− x M x –Mg system. X-ray diffraction and TEM analysis were used to characterise the microstructure of the composite alloy obtained by ball milling. It has been shown that the grain size of MmNi 5− x M x and Mg components were reduced to nanometre range after about 20 h of milling. Besides, a Mm 2 Mg 17 phase of nanometre size was also formed in the milling process. Thus, a composite alloy, referred to as nano-phase composite here, composed of MmNi 5− x M x , Mg and Mm 2 Mg 17 phase of nanometre size was obtained. Hydrogen storage behaviour of the nano-phase composite was compared with that of conventional MmNi 5− x M x alloy by measuring PCT and kinetics. It showed that the hydrogen absorption properties were improved.

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.

Highly reflective nanofiber films based on electrospinning and their application on color uniformity and luminous efficacy improvement of white light-emitting diodes

Based on electrospinning technology, in this study, we fabricated poly(lactic-co-glycolic acid) (PLGA) nanofiber films with high reflectivity and scattering properties. Various films with different thicknesses and fiber diameters were fabricated by changing the electrospinning time and solution concentration, respectively. Detailed optical measurements demonstrate that the film reflectance and scattering ability increase with the thickness, whereas fiber diameter contributes little to both properties. With optimized film thickness and fiber diameter, nanofiber films feature whiteness with a reflectance of 98.8% compared to the BaSO4 white plate. Furthermore, when deposited on the reflector surface of a remote phosphor-converted light-emitting diode lamp, nanofiber films witness a correlated color temperature deviation decrease from 8880 K to 1407 K and a luminous efficiency improvement of 11.66% at 350 mA. Therefore, the nanofiber films can be applied in lighting systems as a highly reflective coating to improve their light efficacy and quality.

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.

Freeform illumination lens design combining energy and intensity mapping

A composite method combining energy and intensity mapping is proposed to address the issue of surface error caused by the irregular sampling phenomenon in freeform illumination lens design. In the combined method, the central region of the freeform lens is designed by the intensity mapping method, whereas the peripheral region is designed by the energy-mapping method. Furthermore, an iterative feedback optimization is added to scale out the application in extended light sources. As an evaluating example, a freeform lens with a 120-deg viewing angle, fitted with an appropriate number of points is designed by the proposed combined method. Compared with that designed by the energy method, the lens forms a more uniform illumination on the target surface without the appearance of a hot spot in the central region. The proposed method also exhibits superiority in extended-source design, where only a one-time optimization is needed to achieve the preset uniformity with the proper choice of coefficients.