Guanwei Liang

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.

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.

ACU improvement of CCT-tunable LED device by electrospun nanofiber film

We fabricated PMMA nanofiber composite diffusion films to improve the angular color uniformity (ACU) of correlated-color-temperature-tunable light emitting diode (CCT-tunable LED) device. Based on electrospinning technology, we prepared diffusion films with different scattering properties by controlling the fiber deposition time. Detailed optical measurement shows that the scattering intensity of PMMA nanofiber films increases with the increase of thickness. The diffuse transmittance and haze are 88%, 96.6% in the visible light, respectively. Furthermore, when applied to the CCT-tunable LED device, the device witnesses a reduced CCT deviation from 630 K to 159 K in a typical CCT range of 5000– 6000 K. Therefore, the proposed nanofiber films can be applied to lighting systems as diffusion films to improve their ACU.

Color Uniformity Enhancement for WLEDs Using Inverted Dispensing Method

The inverted dispensing (ID) method is proposed to fabricate remote phosphor layers (RPLs) with cone-like shapes for white light-emitting diodes (WLEDs) to improve their color uniformity. We introduce surface evolver packages and optical simulations to study the effect of the surface tension on the optical performance of these WLEDs during the ID process. The results show that a decreasing surface tension contributes to a sharpened geometry of the RPL. This sharpened surface geometry is responsible for the optimization of the color uniformity by deflecting blue light towards central angles. The proposed ID method is simple and efficient. The color uniformity performance can be tuned by selecting silicone with a proper surface tension without affecting the total correlated color temperature and sacrificing the WLED’s optical power.