The characteristics of the residual stress on the types of the substrate was investigated with adjusting the V/IIIratio during GaN growth via the HVPE method. GaN single crystal layers were grown on a sapphire substrate and a GaNtemplate under the conditions of V/III ratio 5, 10, and 15, respectively. During GaN growth, multiple hexagonal pits inGaN single crystal were differently revealed in accordance with growth condition and substrate type, and their distributionand depth were measured via optical microscopy(OM) and white light interferometry(WLI). As a result, it was confirmedthat the distribution area and depth of hexagonal pit tended to increase as the V/III ratio increased. Moreover, it was foundthat the residual stress in GaN single crystal decreased as the distribution area and depth of the pit increased throughmeasuring micro Raman spectrophotometer. In the case of GaN growth according to substrate type, the GaN on GaNtemplate showed lower residual stress than the GaN grown on sapphire substrate.
To develop the bright-vivid red- and yellow-inorganic fluorescent pigments with high luminescence properties,A3V5O14 (A = K and Rb) and Cs2V4O11 inorganic pigments were synthesized by a water assisted solid state reaction (WASSR)method and a conventional solid state reaction method. Although impurity peaks corresponding to the AVO3 and AV3O8(A = K, Rb, and Cs) were observed in all samples prepared, the trigonal structure A3V5O14 (A = K and Rb) and orthorhombicstructure Cs2V4O11 were successfully obtained as a main phase. These inorganic pigments showed the broad absorption band(under 550 nm) originated from CT transitions of VO4 polyhedron, and the strong broad red- and green-emission bands dueto 3T2 1A1 and3T1 1A1 transitions of the [VO4]3 group. The A3V5O14 (A = K and Rb) and Cs2V4O11 pigments showeda bright-vivid red- and yellow-body color, where the a* values of the A3V5O14 (A = K and Rb) were +35.5 and +45.9,respectively, and b* value of Cs2V4O11 pigments was +50.3. The L* values of the A3V5O14 (A = K and Rb) and Cs2V4O11inorganic pigments were over +45. These results indicate that the A3V5O14 (A = K and Rb) and Cs2V4O11 inorganic pigmentscould be an attractive candidate as a bright-vivid red- and yellow inorganic pigments.
In the previous study, we reported the result to prepare lithium carbonate powder from various lithium-containedsolution. Therefore, using the lithium hydroxide solution, it is conformed that the reaction could occur thermodynamically,and the recovery rate of lithium was 89.4 %. In this study, we carried out the experiment to prepare lithium carbonate powderthrough gas-liquid reactions with lithium hydroxide solution and CO2 gas using ultrasound energy. In case ultrasonic energyis applied to the reaction of lithium carbonate, the recovery rate of lithium at room temperature was approximately 83.8 %,and the recovery rate of lithium was greatly increased to approximately 99.9 % at 60oC reaction temperature. And whenultrasonic energy is not applied, the particle size of lithium carbonate powder was 7.7 m in D50. But the particle size oflithium carbonate powder was significantly reduced to 8.4 m in D50 under the influence of ultrasonic.
The depletion of fossil fuels and the increase in environmental awareness have led to greater interest in renewableenergy. In particular, solar cells have attracted attention because they can convert an infinite amount of solar energy intoelectricity. Dye-sensitize solar cells (DSSCs) are low cost third generation solar cells that can be manufactured usingenvironmentally friendly materials. However, DSSC photoelectrodes are generally produced by screen printing, which requireshigh temperature heat treatment, and low temperature processes that can be used to produce flexible DSSCs are limited. Toovercome these temperature limitations, this study fabricated photoelectrodes using room-temperature aerosol deposition. Theresulting DSSCs had an energy conversion efficiency of 4.07 %. This shows that it is possible to produce DSSCs and flexibledevices using room-temperature processes.
The difference of plasma resistance between the CAS glass bulk and coating films were compared. Plasmaresistance was confirmed by analyzing the etch rate and the microstructure of the surface when the CAS glass bulk andthe glass coating film were etched with CF4/O2/Ar plasma gas. CAS glass coating film was etched up to 25 times fasterthan the glass bulk. A statistically high correlation between the surface roughness and the etching rate of the coating filmwas derived, and thus, the high surface roughness of the coating film was determined to cause rapid etching. In addition,cristobalite crystals that has a low Ca content and a high Si content, was foamed on the glass coating film. Therefore, theCAS glass coating film is considered to have low plasma resistance compared to the glass bulk.
In this study, phosphor ceramics were fabricated, and optical properties were analyzed for application to nextgenerationautomotive laser headlamps by using a spherical YAG : Ce phosphor with a garnet structure synthesized basedon the spray drying method. The thickness of phosphor ceramic using spherical YAG : Ce phosphor was obtained with100 m, 150 m, and 200 m to investigate the effect of thickness on optical properties such as light conversion efficiency,heat dissipation, luminance and color temperature. The results of this study are expected to play a significant role in themanufacturing process for the fabrication of phosphor ceramic by solving issues such as the high cost and low yield in theconventional liquid method to manufacture YAG : Ce nano fluorescent materials.
Quantum dot efficiency was increased to evaluate reliability and optical characteristics using incidental materials.
Quantum dot was manufactured by wrapping a sandwich type quantum layer using a product with a barrier property toprevent water and oxygen because it is vulnerable to oxygen and moisture. We used the three quantum dot films consistingof quantum dot only and quantum dot products consisting of film and barrier film combined with PET in the quantum dotproduct to evaluate the change over 650 hours under high temperature and high humidity conditions at 60oC and 90 %humidity. As a result, the quantum dot product with Barrier Film has lowered luminance by 8 %, CIE x by 2 % and CIEy by 8 %. Quantum dot products exposed to moisture and oxygen were oxidized and measured low before measurement.