Time filter

Source Type

Lee K.-C.,Korea Photonics Technology Institute KOPTI | Kim S.-M.,Korea Photonics Technology Institute KOPTI | Moon J.-H.,Chonnam National University
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

White light-emitting diodes (LEDs) have dramatically developed and gradually taken over from the conventional light source as the solid-state lighting during the last decade. It is now sufficient for illumination application in performance, while it is still insufficient in color quality. Especially, most of phosphor-converted white LEDs have the poor angular color homogeneity. In this study, we adopted a distinctive phosphor conformal coating technique in the packaging process to reduce the variance of correlated color temperature (CCT) among the packages and spatial CCT in the package. Also, to reduce the spatial CCT variance without considerable shrinkage of luminous efficacy, we applied sub-micrometer scale TiO2 powder as diffuser in the phosphor layer or in the encapsulation layer of white LED with a phosphor conformal coating layer and investigated the effects of titania diffuser on angular color homogeneity and optical performance. Regardless of the diffuser content, spatial CCT variance and luminous efficacy were decreased with the increase of the diffuser content. Nevertheless, among the conditions for achievement of the equivalent in color uniformity, the luminous efficacy in the case of 0.1 wt% diffuser mingled in the encapsulation layer was 20 % higher than in the case of 5 wt% diffuser mingled in the phosphor layer. These phenomena result from differences of light scattering loss caused by 10 times more volume of diffuser mixed in the phosphor layer than in the encapsulation layer. © 2010 SPIE.

Son H.,Chonnam National University | Lee J.K.,Chonnam National University | Kim S.-M.,Korea Photonics Technology Institute KOPTI
Applied Physics Express | Year: 2013

GaN-InGaN vertical-injection light-emitting diodes (VLEDs) having SiO 2 nanorod arrays were demonstrated to enhance the light extraction efficiency and light propagation to the side of the LEDs. The full width at half maximum (FWHM) of the radiation patterns of the VLED having a nano-extractor (115-117°) was more extracted than that of conventional VLED (108-110°). Furthermore, the light output power of the VLEDs having nanorods was enhanced by 7.9% compared with that of the conventional VLEDs. Based on the measured far-field radiation patterns, the nanorods suppressed the total internal reflection and extracted the light to the side of the thin-GaN LEDs. © 2013 The Japan Society of Applied Physics.

Choi P.-J.,Chosun University | Kim J.-Y.,Korea Photonics Technology Institute KOPTI | Kang Y.-J.,Chosun University | Kang Y.-J.,Korea Photonics Technology Institute KOPTI | Kwon M.-K.,Chosun University
Journal of Nanoscience and Nanotechnology | Year: 2014

This study examined the effects of the alignment of ZnO nanorod arrays (NRAs) on the light extraction enhancement of GaN-based light emitting diodes (LEDs), where ZnO NRAs were synthesized hydrothermally. The shape of the ZnO NRAs was controlled using seed layers for flower and vertical structures. Numerical analysis based on the two-dimensional (2D) finite difference of time domain (FDTD) method showed that the extraction efficiency of LED with bare (without ZnO NRA), vertical ZnO NRA and flower shaped ZnO NRA was 37%, 60% and 49%, respectively. The optical output power of the LEDs with vertical ZnO NRA and flower ZnO NRA was improved by 50% and 30% compared to that of the LED without ZnO NRA at an input current of 100 mA. These results suggest that the vertical alignment of ZnO NRA is important for enhancing the light extraction of GaN based LEDs. Copyright © 2014 American Scientific Publishers.

Kim J.P.,Korea Photonics Technology Institute KOPTI | Song S.B.,Korea Photonics Technology Institute KOPTI
Applied Surface Science | Year: 2011

In this study, an orange-red silicate phosphor that is used in light emitting diodes (LEDs) was coated with a SiO2 blocking layer via a sol-gel reaction of tetra-ethyl ortho-silicate (TEOS) to investigate its reliability as an encapsulant. A sol-gel coating protects the phosphor surface from moisture and reactive materials and improves the reliability of the phosphor. The efficacy of the phosphor coating following an 85 °C and 85 relative humidity (Rh)% test decreased by 7%, whereas an uncoated phosphor coating decreased by 35%. A SiO2 sol-gel coating decreases the luminous efficiency by a small amount with each coating.

Lee K.-H.,Gwangju Institute of Science and Technology | Kim S.-M.,Korea Photonics Technology Institute KOPTI | Jeong H.,Gwangju Institute of Science and Technology | Pak Y.,Gwangju Institute of Science and Technology | And 10 more authors.
Advanced Materials | Year: 2013

All-solution-processed transparent thin film transistors (TTFTs) are demonstrated with silver grid source/drain electrodes, which are fabricated by printing and subsequent silver nanoparticles solution coating, which allows continuous processing without using high vacuum systems. The silver grid electrode shows a reasonable transmittance in visible range, moderate electrical conductance and mechanical strength. The TTFTs are employed to drive liquid crystal cells and demonstrate a successful switching operation. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Seo T.H.,Chonbuk National University | Lee K.J.,Chonbuk National University | Park A.H.,Chonbuk National University | Hong C.-H.,Chonbuk National University | And 8 more authors.
Optics Express | Year: 2011

We report GaN-based near ultraviolet (UV) light emitting diode (LED) that combines indium tin oxide (ITO) nanodot nodes with two-dimensional graphene film as a UV-transparent current spreading electrode (TCSE) to give rise to excellent UV emission efficiency. The light output power of 380 nm emitting UV-LEDs with graphene film on ITO nanodot nodes as TCSE was enhanced remarkably compared to conventional TCSE. The increase of the light output power is attributed to high UV transmittance of graphene, effective current spreading and injection, and texturing effect by ITO nanodots. © 2011 Optical Society of America.

Kim S.-M.,Korea Photonics Technology Institute KOPTI | Lee K.-H.,Gwangju Institute of Science and Technology | Jung G.Y.,Gwangju Institute of Science and Technology
CrystEngComm | Year: 2013

We fabricated InxGa1-xN multiple quantum well (MQW) light-emitting diodes (LEDs) on an air void embedded SiO2 mask using a simple process (silver (Ag) deposition, SiO2 capping, and high-temperature annealing). Ag was volatilized in the MOCVD process and formed an air void, as revealed by energy dispersive X-ray spectroscopy images. The light output power (at 20 mA) of the LED using epitaxial lateral overgrowth on the SiO2 mask (47.8%) and LED with the air void embedded SiO 2 mask (96.8%) are enhanced compared to conventional LEDs. From reflectance measurements, the enhancement of LEDs with an air void embedded SiO2 mask could be mainly explained by the increased high incident angle specular reflectance. © 2013 The Royal Society of Chemistry.

Lee K.-H.,Gwangju Institute of Science and Technology | Kim S.-M.,Korea Photonics Technology Institute KOPTI | Jeong H.,Gwangju Institute of Science and Technology | Jung G.-Y.,Gwangju Institute of Science and Technology
Soft Matter | Year: 2012

We develop an innovative solution processable edge lithography, which we call double-dewetting edge lithography (DDEL). The polymer solution spontaneously dewets the hydrophobic regions and covers only hydrophilic regions on a surface energy-engineered substrate, which is achieved by a combination of conventional photolithography and a subsequent hydrophobic treatment of the exposed areas. Then, the secondary dewetting occurs through a coffee stain effect during the solvent evaporation, leaving polymer edge patterns behind. The whole double-dewetting phenomenon is complete within 1 s. This technique is a fast, cost-effective and easy direct solution patterning method, which enables nanoscale polymer edge patterns to be produced from various micron-scale platforms including lines, angular and irregular shapes.

Kim K.S.,Gwangju Institute of Science and Technology | Kim K.S.,Samsung | Song H.,Gwangju Institute of Science and Technology | Nam S.H.,Gwangju Institute of Science and Technology | And 4 more authors.
Advanced Materials | Year: 2012

A periodically aligned submicron ZnO hemispheres array was embedded into a TiO 2 nanoparticulate thin film (thickness; ca. 12 μm) as a photoanode for dye-sensitized solar cells (DSSCs). The ZnO hemisphere array provided light scattering centers that excited more dyes and direct electron pathways to the electrodes, which is beneficial for high efficiency DSSCs. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

PubMed | Pukyong National University and Korea Photonics Technology Institute KOPTI
Type: Journal Article | Journal: Lasers in surgery and medicine | Year: 2016

Artificial skin phantoms have been developed as an alternative tissue for human skin experiments due to convenient use and easy storage. However, fabricating both thin (100m) epidermis and relatively thick dermis is often cumbersome, and most developed phantoms have hardly reflected specific human skin types. The objective of this study was to fabricate skin phantoms with 3D printing technique to emulate various human skin types (I-VI) along with the corresponding optical and mechanical properties for laser tattoo removal.Both gelatin and agar powders were mixed with coffee and TiO2 particles to fabricate skin phantoms with materials properties for various skin types (I-VI). A 3D printer was employed to precisely control the thickness of each phantom for epidermis and dermis layers. A number of concentrations of the coffee and TiO2 particles were used to determine the degree of absorption and scattering effects in various skin types. The optical properties between 500 and 1,000nm for the fabricated phantoms were measured by double-integrating spheres with an inverse adding-doubling (IAD) algorithm. Optical coherence tomography (OCT) and rheometer were also utilized to evaluate optical (absorption and reduced scattering coefficients) and mechanical properties (compression modulus) of the fabricated phantoms, respectively.Visible color inspections presented that the skin phantoms for types I, III, and VI similarly emulated the color space of the human skin types. The optical property measurements demonstrated that the absorption (a) and reduced scattering ((s)) coefficients decreased with wavelengths. Compared to the human skin type VI, a dermis phantom represented quite equivalent values of a and (s) whereas an epidermis phantom showed up to 30% lower a but almost identical (s) over the wavelengths. The OCT measurements confirmed that the thicknesses of the epidermis and the dermis phantoms were measured to be 138.500.01m and 0.810.04mm, respectively. The mechanical properties of the phantoms mixed with the agar volume of 40% yielded a compression modulus of 83.714.8kPa, which well corresponded to that of human forearm skin (50-95kPa).The 3D printing technique was able to reliably fabricate the double-layered phantoms emulating a variety of skin types (I-VI) along with the comparable optical and mechanical properties. Further investigations will incorporate artificial chromophores into the fabricated skin phantoms to reliably evaluate the new therapeutic wavelengths for laser tattoo removal.

Loading Korea Photonics Technology Institute KOPTI collaborators
Loading Korea Photonics Technology Institute KOPTI collaborators