Hong Jeong Yu

Characterization and Photoluminescence of CdS Nanoparticles Synthesized in Diethyl Ether-Sodium Dioctylsulfosuccinate-Water Microemulsion System

Spherical cadmium sulfide (CdS) nanoparticles, 4–5 nm in diameter, were synthesized using an aqueous cadmium nitride [Cd(NO3)24H2O] and sodium sulfide [Na2S9H2O] solution in a microemulsion system. The effects of the water to surfactant molar ratio (W = [water]/[surfactant]), the concentration of precursors, the Cd to S precursor ratio, and the density of the ultrasonic wave on the properties of the CdS nanoparticles were examined. The luminescent properties and the size effect of the nanoparticles were characterized using UV–vis absorption and photoluminescence (PL) spectra. The PL emission intensity did not change significantly with an increase in precursor and surfactant concentrations. The absorption edge and PL peak energy of the CdS nanoparticles shifted to shorter wavelengths with an increase in cadmium nitride concentration owing to a phase change and a decrease in CdS nanoparticle size.

Preparation of Blue-Emitting Phosphorescent Iridium(III) Complex Under Ultrasound Reaction

F2MeIrpic (Iridium(III)bis[2-(2′,4′-difluorophenyl)-4-methyl pyridinato-N,C2′] picolinate) was synthesized to develop a blue-emitting phosphorescent Ir(III) complex. The synthesized F2MeIrpic showed sky blue light with the maximum PL peak at 470 nm. Generally the reaction time and maximum yield of F2MeIrpic were known to be 78 hours and 28%, respectively. The reaction is composed of three steps which are the synthesis of ligand (F2Meppy), Ir-dimer and F2MeIrpic with Ir-dimer and picolinic acid. The synthesis of F2MeIrpic is a rate determining step. The solubility and dispersibility of Ir-dimer in solvent are important reaction parameters which determine reaction time and yield, because Ir-dimer is not soluble in almost all solvent. Among various solvents Tetrahydrofuran(THF) was the best solvent to solve Ir-dimer. Ir-dimer was dispersed well by an ultra-sonication in the solvent during reaction. The reaction time was reduced to 36 hours and yield was enhanced to 45% by ultra sound in THF.

White emission from CdSe/ZnSe nanoparticles combining with 400, 430 and 460nm InGaN LED

White light emitting diodes (LEDs) were fabricated combining InGaN LED chip as the excitation source and CdSe/ZnSe as the phosphor. CdSe/ZnSe nanoparticles were synthesized via wet chemical method using CdO, zinc stearate, TOP Se as precursors. 4.5 and 5.3nm diameter CdSe/ZnSe nanoparticles with emission peak at 540 and 620nm, respectively, were obtained. CdSe nanoparticle phosphors were coated onto the 460, 430 and 400nm LED chips to fabricate white LEDs. As the shorter wavelength of LED chip was applied to excitation source, the luminous efficiency of white LED was enhanced. The luminous efficiencies of 400, 430, and 460nm excitation white LEDs were 2.15, 3.96 and 6.57 lm/W, respectively at 20 mA. The corresponding CIE-1931 coordinates were (0.34, 0.30), (0.30, 0.32), and (0.31, 0.29). The color rendering index (CRI) of white LED showed similar values ; 65.1, 65.5, and 66.2.

White light emission from blue InGaN LED with hybrid phosphor

In this work we fabricated white LEDs using a blue InGaN LED precoated conjugated copolymer / QDs composite (green-emitting Poly [(9,9-dioctyl-2,7-divinylenefluorenylene)-alto-co-(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene] / red-emitting CdSe quantum dots) as hybrid phosphor. The emission peak wavelengths of blue, green and red emissions in spectra are 462 and 618 nm respectively. Green-emitting polymer has two emission peaks (515 and 543nm). The subpeak of polymer (515 nm) is covered by absorption of QDs. Therefore the emission of first peak is decreasing as increasing the ratio of QDs while the emission of QD (618 nm) is increasing. Therefore CIE-1931 coordinate, the color temperature (7c) and the color rendering index (Ra) were changed by the different ratio of QDs to copolymer. The white LED of the hybrid phosphor containing 20 wt% QDs has a luminous efficiency of 44.2 lm/W at 20 mA with a CIE-1931 coordinate of (0.3297, 0.3332), Tc of 5620 K and Ra of 75.3.