• Bulletin of the Korean Chemical Society
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• v.35 no.1
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• pp.135-140
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• 2014

A bent-shape triazolyl derivative was synthesized via click chemistry, and its photophysical property was investigated in various solvents. In contrast to the invisible ultraviolet emission of other solutions, the chloroform solution exhibited a blue light emission at 460 nm. Furthermore, the blue fluorescence intensified as the UV exposure time at 365 nm increased. On the basis of $^1H$-NMR, pH paper, and acid-addition studies, we confirmed that chloroform was decomposed into HCl with the aid of the triazolyl derivative. The density functional theory calculations suggested that the eye-detectable blue fluorescence was attributed to an intramolecular charge transfer process of the protonated triazolyl derivative in the chloroform solution.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.32-35
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• 2006

For the white UV-LED applications, $Eu^{2+}$-activated calcium aluminium silicate phosphors were synthesized for the first time and the structures and luminescence characteristics of these phosphors were investigated. The phosphors in this study emitted blue. green or blue-green light depending on the starting materials for synthesis. In addition, the structure was also changed when the different starting materials were used. When CaO and $CaCO_3$ was used as a starting material. tetragonal $Ca_2Al_2SiO_7$ was formed and blue-green and pure green light was emitted. respectively. However. in the case of $CaSiO_3$, triclinic $CaAl_2Si2O_8$ was formed and only pure blue emission was detected. The maximum emission intensity was obtained from $CaAl_2Si_2O_8:Eu^{2+}$ phosphors, which intensity was about 1.4 times higher than that of YAG:$Ce^{3+}$ phosphor used for blue LED.

• 한국정보디스플레이학회:학술대회논문집
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• 2000.01a
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• pp.29-30
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• 2000

CaS:Pb thin film used as phosphor layer in electroluminescent devices were deposited by an atomic layer deposition (ALD). The photoluminescence emission and excitation spectra were measured at 5 and 300K for the $CaS:Pb^{2+}$ phosphors with different Pb concentration from 0.001 at.% to 0.648 at.%. The emission spectra of these samples were characterized as UV emission and blue emission with the center of peak around 360 and 425nm, respectively. The UV emission was dominant at the low $Pb^{2+}$ concentration of 0.001 at%, whereas with increase of Pb concentration, the blue emission became a major component and to longer wavelength.

• Journal of the Korean Ceramic Society
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• v.43 no.5 s.288
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• pp.304-308
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• 2006

We have synthesized a $Eu^{2+}-activated\;Sr_3MgSi_2O_8$ blue phosphor and $(Sr,Ba)_2SiO_4$ yellow phosphor and prepared white LEDs by combining these phosphors with a InGaN UV LED chip. Three distinct emission bands from the InGaN-based LED and the two phosphors are clearly observed at 405 nm, 460 nm and at around 560 nm, respectively. The 405 nm emission band is due to a radiative recombination from a InGaN active layer. This blue emission was used as an optical transition of the $Sr_3MgSi_2O_8:Eu$ blue phosphor and $(Sr,Ba)_2SiO_4:Eu$ yellow phosphor. The 460 nm and 560 nm emission band is ascribed to a radiative recombination of $Eu^{2+}$ impurity ions in the $Sr_3MgSi_2O_8:Eu$ and $(Sr,Ba)_2SiO_4$ host matrix. As a consequence of a preparation of UV White LED lamp using the $Sr_3MgSi_2O_8:Eu$ blue phosphor and $(Sr,Ba)_2SiO_4:Eu$ yellow phosphor, the highest luminescence efficiency was obtained at the ration of epoxy/two phosphor (1/0.2361). At this time, the CIE chromaticity was CIE x = 0.3140, CIE y = 0.3201 and CCT (6500 K).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.9
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• pp.701-707
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• 2010

We have synthesized new pure blue-emitting hyperbranched polyfluorene (Hyper-PDHF) through $A_2$ and $B_3$ type monomers via Suzuki coupling polymerization. The weight-average molecular weights ($M_w$) of the Hyper-PDHF was found about 35,000 with polydispersity index as 6.1. The UV absorption peak of the Hyper-PDHF film was at around 335 nm which was far blue shifted than that of linear PDHF film which was found at 380 nm. The pure blue photoluminescene (PL) peak of the Hyper-PDHF was measured at 419 nm as main emission with 397 and 444 nm as shoulder peaks. The Hyper-PDHF showed also higher PL quantum efficiency in solution than linear PDHF (Hyper-PDHF, $\Phi$sol =0.81; PDHF, $\Phi$sol=0.78). The annealed PDHF film (5 hrs on hot plate at $80^{\circ}C$) showed increased shoulder peak emissions and emission color was changed into the green emission. But, Hyper-PDHF film shows almost no excimer emission peak even the film was annealed. The enhanced PL efficiency and no excimer emission of Hyper-PDHF results from the inhibition of excimer formation by the introduction of the hyperbranched system into the polyfluorene backbone.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.473-474
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• 2005

Blue-emitting polymers containing carbazole units In main chains were synthesized by palladium catalyzed polycondensation of aniline with dibromo-substituted monomers such as 3,6-dibromocarbazole, N-(2-ethylhexyl)-3,6-dibromocarbazole, and bis[6-bromo-N-(2-ethylhexyl)-carbazole-3-yl], respectively. All synthesized polymers exhibited relatively good solubility in common organic solvents, considerable molecular weights and high resistance to thermal degradation. From UV-Vis absorption and photoluminescence (PL) spectra of these solution-processable polymers, $\lambda_{max,UV}$ were in the range of 290 ~ 340 nm and $\lambda_{max,PL}$ were in the blue emission range of 440 ~ 478 nm, The polymers had HOMO energy (-5.19 ~ -5.64 eV) and wide band gap energy (2,91 - 3.42 eV).

• Journal of Biosystems Engineering
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• v.35 no.2
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• pp.124-131
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• 2010

Chlorophyll fluorescence has been researched for assessing fruit post-harvest quality and condition. The objective of this preliminary research was to investigate the potential of fluorescence spectroscopy for measuring apple fruit quality. Ultraviolet (UV) and blue light was used as an excitation source for inducing fluorescence in apples. Fluorescence spectra were measured from 'Golden Delicious' (GD) and 'Red Delicious' (RD) apples using a visible/near-infrared spectrometer after one, three, and five minutes of continuous UV/blue light illumination. Standard destructive tests were performed to measure fruit firmness, skin and flesh color, soluble solids and acid content from the apples. Calibration models for each of the three illumination time periods were developed to predict fruit quality indexes. The results showed that fluorescence emission decreased steadily during the first three minutes of UV/blue light illumination and was stable within five minutes. The differences were minimal in the model prediction results based on fluorescence data at one, three or five minutes of illumination. Overall, better predictions were obtained for apple skin chroma and hue and flesh hue with values for the correlation coefficient of validation between 0.80 and 0.90 for both GD and RD. Relatively poor predictions were obtained for fruit firmness, soluble solids content, titrational acid, and flesh chroma. This research has demonstrated that fluorescence spectroscopy is potentially useful for assessing selected quality attributes of apple fruit and further research is needed to improve fluorescence measurements so that better predictions of fruit quality can be achieved.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.654-656
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• 2004

The effect of excitation energy and various dopants(Eu and Ce) on the emission wavelength and intensity were investigated. According to PL spectra, SrO-$Al_2O_3$ phosphors had wide absorption band at nUV. By substituting Ce for Eu, the emission band and excitation wavelength were shifted to shorter wavelength. Ce doped $SrAl_2O_4$ and $Sr_4Al_{14}O_{25}$ showed greenish blue(475nm) and blue(400nm), respectively.

• Bulletin of the Korean Chemical Society
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• v.26 no.11
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• pp.1776-1782
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• 2005

ZnSe/ZnS, UV-blue luminescent core shell quantum dots, were synthesized via a thermal decomposition reaction of organometallic zinc and solvent coordinated Selenium (TOPSe) in a hot solvent mixture. The synthetic conditions of the core (ZnSe) and the shell (ZnS) were independently studied at various reaction temperature conditions. The obtained colloidal nanocrystals at corresponding temperatures were characterized for their optical properties by UV-vis, room temperature solution photoluminescence (PL) spectroscopy, and further obtained powders were characterized by XRD, TEM, and EDXS analyses. The synthetic temperature condition to obtain the best PL emission intensity for the ZnSe core was 300 ${^{\circ}C}$, and for the optimum shell capping, the temperature was 135 ${^{\circ}C}$. At this temperature, solution PL spectrum showed a narrow emission peak at 427 nm with a PL efficiency of 15%. In addition, the measured particle sizes for the ZnSe/ZnS nanocomposite via TEM were in the range of 5 to 12 nm. Furthermore, we have synthesized water-soluble ZnSe/ZnS nanoparticles by capping the ZnSe/ZnS hydrophobic surface with mercaptoacetate (MAA) molecules. For the obtained aqueous colloidal solution, the UV-vis spectrum showed an absorption peak at 250 nm, and the solution PL emission spectrum showed a peak at 425 nm, which is similar to that for hydrophobic quantum dot ZnSe/ZnS. However, the calculated PL efficiency was relatively low (0.1%) due to the luminescence quenching by water and MAA molecules. The capping ligand was also characterized by FT-IR spectroscopy, with the carbonyl stretching peak in the mercaptoacetate molecule appearing at 1575 $cm ^{-1}$. Finally, the particle sizes of the MAA capped ZnSe/ZnS were measured by TEM, showing a range of 12 to 17 nm.

• Journal of the Korean Ceramic Society
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• v.41 no.8
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• pp.573-577
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• 2004

We have synthesized a Eu$^{2＋}$-activated Sr$_3$MgSi$_2$ $O_{8}$ blue phosphor and investigated an attempt to develop blue LEDs by combining it with a InGaN blue LED chip (Len=405 nm). The InGaN-based Sr$_3$MgSi$_2$ $O_{8}$：Eu LED Lamp shows two bands at 405 nm and 460 nm. The 405 nm emission band is due to a radiative recombination from a InGaN active layer. This 405 nm emission was used as an optical transition of the Sr$_3$MgSi$_2$ $O_{8}$：Eu phosphor. The 460 m emission band is ascribed to a radiative recombination of Eu$^{2＋}$ impurity ions in the Sr$_3$MgSi$_2$ $O_{8}$ host matrix. As a consequence of a preparation of W blue LED Lamp using the Sr$_3$MgSi$_2$ $O_{8}$：Eu blue phosphor, the highest luminescence efficiency was obtained at the ration of epoxy/blue phosphor(1/0,202). At this time, the CIE chromaticity was x=0.1417 and y=0.0683.