In this paper, we report on the growth and optical characteristics of white-LED without fluorescent material. The growth of DH (double heterostructure) with AlGaN active layer was performed on a n-GaN/(0001) Al2O3 by the mixedsource HVPE and multi-sliding boat. The CRI (color rendering index) of packaging device charged in the range 72-93 with CIE chromaticity coordinates (x = 0.26~0.34, y = 0.31~0.40). And CCT (correlated color temperature) values was measured 5126~10406 K with increasing injection current. The CIE point of conventional phosphor white LED shifts blue region, but CIE point of non-phosphor white LED shifts opposite direction. These results show the mixed-source HVPE can be possible to newly fabricate method of phosphor free white LED with high CRI value.
Effect of the processing variables on the formation of Pb(Sc1/2Nb1/2)O3 (hereafter PSN) thin layers prepared on Pt(111)/Ti/SiO2/Si substrates using the sol-gel and the spin coating method has been studied. After each deposition, the coated films were heated at 370oC for 5 min. Then they were finally sintered at temperature range of 600~700oC by RTA(rapid thermal annealing). The final multilayered films showed a (111) preferred orientation. On a while, the layer-bylayer crystallization of multilayered amorphous thin films without the intermediate heating exhibited a (100) preferred orientation. In case of heat treatment in the tube furnace with the heating rate of 4oC/min, (100) and (111) oriented thin layers were formed simultaneously. The microstructure of the deposited films were dense and crack-free with thickness of 300nm, irrespective of the processing variables.
Si-doped GaAs single crystals were grown by vertical gradient freeze using PBN crucibles. The amount of oxide layer B2O3 in PBN crucible was changed (0~0.2 wt%) and measured the concentration of carriers. The segregation
coefficients of Si in GaAs melt decreased rapidly from initial 0.1 to 0.01 as the amount of B2O3 increases. At the same time, concentration of carriers was shown to decrease. It is likely that the reaction between dopant Si and B2O3 in GaAs melt results in the reduction of Si dopants (donor) while increase in the amount of boron (acceptor). The thin layer of B2O3 glass in PBN crucible was proved to be a better way to reduce defect formation rather than the total amount of B2O3.
The glass-ceramic of the Li2O-Al2O3-SiO2 system was investigated to develop the low thermal expansion materials. The glass of this system was heat treated at 775oC for 2 h for nucleation and subsequently at 825~900
oC for 2 h for crystallization. The crystal structure of the glass-ceramic of this system was a single phase of β-quartz solid solution (LixAlxSi1 − xO2). The thermal expansion of the glass-ceramic showed 4.40 × 10−7~1.33 × 10−6
K−1 between 25~300oC and 1.56 × 10−6~2.53 × 10−6K−1 between 25~800
oC, higher than lower temperature range. The mechanical strength remained
almost same at around high 110 MPa with heating temperature changes.
The turbid/translucent, near colorless (milky) metamorphic sapphire samples from Sri Lanka have been characterized after the heat treatment in N2 at 1650
oC. As-received sapphire specimens became bluish-colored and exhibited more clarity after the heat treatment. It was found that the color change at inclusions zoning region is attributed by the dissolution. As received samples contain the micro/nano inclusions such as rutile (TiO2), ilmenite (FeTiO3), spinel (MgAl2O4)/ulvospinel (Fe2TiO4) and apatite (Ca5(PO4)3), which were dissolved by the heat treatment and form the blue color through Fe2+/Ti4+
charge transferring. The microstructures become different because as the dissolution of apatite (Ca5(PO4)3(OH,F,Cl)) in alumino silicates (Al2SiO5) occurred, resulting in morphological change with the appearance of (Ca, Mg, Al) silicate on the surface. Both as-received and heat treated samples showed the rhombohedral crystal structure of Al2O3.
Mong Hsu rubies from Myanmar were heat treated in oxidizing (oxygen) atmosphere at 1650oC for 1 hour. The investigations of the micro-structural defects in the samples before and after heat treatment have been carried out by the variety of analysis techniques of FTIR, UV-VIS-NIR and SEM-EDS. It was found that after heat treatment the dark blue cores region were disappeared and turned to orange red color with the presence of the dense cloudy brownish colored tiny particles in and near former blue zoning. As-received ruby samples only revealed the presence of FTIR absorption peaks of
diaspore, boehmite and O-H stretching, at 1986, 2115 and 3078/3319 cm−1
, respectively. The UV-VIS-NIR absorption of asreceived and heat treated ruby samples similarly showed peaks at 405, 554 and 693 nm associated with Cr3+, but for the same samples, the absorption peak of heat-treated ruby samples at 693 nm was somewhat stronger than that of the untreated ruby samples. Especially the presence of Cr3+ peaks at 659 and 675 nm was found obviously in as-received ruby samples only. The SEM-EDS investigation disclosed the micro-porous defect structures commonly related to the core
regions of the untreated ruby samples, which after heat treatment in an oxidizing environment those defect features have been dissolved into the host phase resulting in the lightening or disappearance of the dark coloration of ruby core.
The surface characteristics of Zachery-treated turquoise stones have been studied in detail with a comparison of
natural and plastic-impregnated turquoise. The SEM-EDS analysis exhibited that Zachery-treated turquoise was characterized
by the uniform distribution of potassium element through the specimen and did not show the sharp crystalline SiO2 facet
and boundary phase which are common in natural ore. The potassium element shown in the Zachery-treated turquoise
seemed to be occurred during the treatment process for the improvement of durability. The bar-shaped crystals observed in
the pore was found to be a feature of Zachery treated turquoise and are expected to influence on their stability and
durability, while the pore sizes in turquoise stones depends on the parameter of the treatment procedure.
The accelerated life time test of the MLCCs with different BaTiO3 particle sizes were conducted at 150℃, 75 V
condition and the effect of BaTiO3 particle size on the breakdown voltage and degradation characteristics of MLCCs was
investigated. The MLCCs were prepared by using the BaTiO3 particles having the size of 0.525 μm, 0.555 μm, 0.580 μm
and Ni-electrode, respectively. The MLCCs which have the particle size of 0.525 μm, 0.555 μm, and 0.580 μm, respectively
were confirmed to meet the standard requirements of X5R (change capacitance within ± 15 % at −55~85℃) by TCC
(Temperature Coefficient of Capacitance). The effect of the BaTiO3 particle size on the insulation resistance behavior of
MLCCs was confirmed by BDV (Breakdown Voltage) measurements and the cause and degree of degradation of MLCCs
were characterized by XPS analysis after the accelerated life test. The MLCCs with 0.525 μm-BaTiO3 showed better
insulation resistance and BDV characteristics compare to other MLCCS and XPS analysis revealed that the MLCCs
degradation is caused by the NiO peak and BaTiO3 peak decrease