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Excitation-Dependent Emissive Properties of Silicate Phosphor for Light Converted LEDs
Baojiu Chen,정준호,M. Jayasimhadri,장기완,Ho Sueb Lee,Eunjin Cho,Soung Soo Yi,정중현 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.4
A phosphor with the designed composition 1.99SrO2-1.0MgO-1.6SiO2-0.01Eu2O3 was prepared via a solid state reaction in a reducing atmosphere (90%N2/10%H2). The crystal structure of the phosphor was identified by using X-ray diffraction (XRD). The morphology of the phosphor particles was examined by using scanning electron microscopy (SEM). The optical properties of the emission spectra and the chromaticity coordinates were studied. The emission spectra were found to depend on the excitation wavelengths; thus colors in a wide region could be obtained by combining the prepared phosphor and light-emitting diodes (LEDs) with proper emitting wavelengths.
The Effect of Modified Gravity on the Odds of the Bound Violations of the Turn-around Radii
Lee, Jounghun,Li, Baojiu American Astronomical Society 2017 The Astrophysical Journal Vol.842 No.1
<P>The turn-around radii of the galaxy groups show the imprint of a long battle between their self-gravitational forces and the accelerating space. The standard Lambda CDM cosmology based on the general relativity (GR) predicts the existence of an upper bound on the expectation value of the turn-around radius that is rarely violated by individual galaxy groups. We speculate that a deviation of the gravitational law from GR on the cosmological scale could cause an appreciable shift of the mean turn-around radius to higher values and make the occurrence of the bound violation more probable. Analyzing the data from high-resolution N-body simulations for two specific models with modified gravity (MG) and the standard GR+Lambda CDM cosmology, we determine the turn-around radii of the massive Rockstar groups from the peculiar motions of the galactic halos located in the bound zone where the fifth force generated by MG is expected to be, at most, partially shielded. We detect a 4 sigma signal of difference in the odds of the bound violations between a fiducial MG and the GR models, which proves that the odds of the bound violations increase with the strength of the fifth force produced by the presence of MG. The advantage of using the odds of the bound violations as a complementary diagnostics to probe the nature of gravity is discussed.</P>
Co-precipitation synthesis and characterization of Bi3+, Eu3+ co-doped nanocrystal Gd2WO6 phosphors.
Tian, Yue,Chen, Baojiu,Hua, Ruinian,Cheng, Lihong,Zhong, Haiyang,Sun, Jiashi,Wang, Bo,Wan, Jing,Lu, Weili,Jang, Kiwan American Scientific Publishers 2010 Journal of nanoscience and nanotechnology Vol.10 No.3
<P>Eu3+ single-doped and Bi3+/Eu3+ co-doped nanocrystal Gd2WO6 phosphors were successfully synthesized via a co-precipitation reaction. The structure and morphology of the phosphors were characterized by using X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The influence of Bi(3+)-doping concentration on the excitation and emission spectra was studied. It was found that the introduction of Bi3+ can greatly affect the charge transfer band and the luminescence intensity of Eu3+ but does not cause a change in the profile of emission spectra of Eu3+.</P>
MASSIVE GRAVITY WRAPPED IN THE COSMIC WEB
Shim, Junsup,Lee, Jounghun,Li, Baojiu IOP Publishing 2014 The Astrophysical journal Vol.784 No.1
<P>We study how the filamentary pattern of the cosmic web changes if the true gravity deviates from general relativity (GR) on a large scale. The f(R) gravity, whose strength is controlled to satisfy the current observational constraints on the cluster scale, is adopted as our fiducial model and a large, high-resolution N-body simulation is utilized for this study. By applying the minimal spanning tree algorithm to the halo catalogs from the simulation at various epochs, we identify the main stems of the rich superclusters located in the most prominent filamentary section of the cosmic web and determine their spatial extents per member cluster to be the degree of their straightness. It is found that the f (R) gravity has the effect of significantly bending the superclusters and that the effect becomes stronger as the universe evolves. Even in the case where the deviation from GR is too small to be detectable by any other observables, the degree of the supercluster straightness exhibits a conspicuous difference between the f (R) and the GR models. Our results also imply that the supercluster straightness could be a useful discriminator of f (R) gravity from the coupled dark energy since it is shown to evolve differently between the two models. As a final conclusion, the degree of the straightness of the rich superclusters should provide a powerful cosmological test of large scale gravity.</P>
MODIFIED GRAVITY SPINS UP GALACTIC HALOS
Lee, Jounghun,Zhao, Gong-Bo,Li, Baojiu,Koyama, Kazuya IOP Publishing 2013 The Astrophysical journal Vol.763 No.1
<P>We investigate the effect of modified gravity on the specific angular momentum of galactic halos by analyzing the halo catalogs at z = 0 from high-resolution N-body simulations for a f (R) gravity model that meets the solar-system constraint. It is shown that the galactic halos in the f (R) gravity model tend to acquire significantly higher specific angular momentum than those in the standard Lambda CDM model. The largest difference in the specific angular momentum distribution between these two models occurs for the case of isolated galactic halos with mass less than 10(11) h(-1) M-circle dot, which are likely least shielded by the chameleon screening mechanism. As the specific angular momentum of galactic halos is rather insensitive to other cosmological parameters, it can in principle be an independent discriminator of modified gravity. We speculate a possibility of using the relative abundance of low surface brightness galaxies (LSBGs) as a test of general relativity given that the formation of the LSBGs occurs in fast spinning dark halos.</P>
Optical temperature sensing properties of Yb3+/Tm3+ co-doped NaLuF4 crystals
Lili Tong,Xiangping Li,Ruinian Hua,Lihong Cheng,Jiashi Sun,Jinsu Zhang,Sai Xu,Hui Zheng,Yanqiu Zhang,Baojiu Chen 한국물리학회 2017 Current Applied Physics Vol.17 No.7
Yb3þ/Tm3þ and Yb3þ/Er3þ co-doped NaLuF4 crystals were synthesized by a facile hydrothermal method. The optical temperature sensing properties of Tm3þ based upon its two thermally coupled energy levels 3F2, 3 and 3H4 were systematically investigated by means of fluorescence intensity ratio (FIR) technique. The 980 nm laser-induced thermal effect on Tm3þ doped NaLuF4 crystals was studied by using Er3þ doped sample as thermal probe. The temperature sensitivity of Tm3þ in NaLuF4: Yb3þ/Tm3þ crystals shows a nonlinear dependence on temperature, and the maximum value is about 0.00045 K『1 at 600 K. The accuracy and reliability of the optical thermometry based on Tm3þ in NaLuF4: Yb3þ/Tm3þ crystals has been checked by using Yb3þ/Er3þ co-doped sample as temperature sensing unit. The results demonstrate that NaLuF4: Yb3þ/Tm3þ crystals have good sensing stability and may have potential application for the optical thermometry.