• Current Applied Physics
• /
• v.18 no.11
• /
• pp.1359-1367
• /
• 2018

In this work, we investigated the spectroscopic properties of $LiY_xSr_yZrO_{3+{\alpha}:Eu^{3+}$, a red emitting nanophosphor based on $SrZrO_3$ perovskite. The synthesis process was an auto-combustion process. X-ray diffractograms show the orthorhombic structure of $SrZrO_3$. Photoluminescence (PL) excitation spectra display a split charge transfer band revealing the presence of two possible sites for the $Eu^{3+}$ ions. The emission spectra at 231 nm excitation illustrate the dominance of the $^5D_0-^7F_1$ transition, which is an indication that the smaller sized $Eu^{3+}$ ions are mostly situated at the more ordered (symmetric) $Sr^{2+}$ sites. The emission spectra at 292 nm & 397 nm excitations show the dominance of $^5D_0-^7F_2$ transition which suggests some of the $Eu^{3+}$ ions are also situated at the distorted $Zr^{4+}$ sites. Both the intensity parameters, asymmetry ratio and the decay lifetimes of the nanophosphors show dependence on $Y^{3+}$ concentration, signifying a modification in the host structure. Maximum quantum efficiency value of ${\approx}46%$ was obtained for the nanophosphors which indicate the need for improvement for practical applications. CIE coordinates show the suitability of this phosphor for both red emission in LED and as a complementary colour for white LED applications.

• Journal of the Korean Ceramic Society
• /
• v.39 no.3
• /
• pp.240-244
• /
• 2002

The GdOBr:Ce phosphor were prepared by solid state reaction using starting chemicals of $Gd_2O_3,\;CeO_2\;and\;NH_4Br$. Under 370nm UV excitation, GdOBr:Ce phosphors showed blue emission band with a spectral range of 410∼430nm. The maximum photoluminescence(PL) emission intensity was observed at 2mol% Ce content. In order to look for feasibility of application for low voltage filed emission display, cathodoluminescence(CL) of GdOBr:Ce phosphors were measured. CL emission spectra was found to be in the range of 410∼430nm, which is the same as PL spectra. The phosphors with 1mol% Ce concentration showed the maximum CL emission intensity. For the comparison of degradation property of the prepared phosphors with commercial ones, the electron beam was applied for 10min. From the result, GdOBr:Ce could be used as a blue phosphor for FED.

• Journal of the Korean Vacuum Society
• /
• v.16 no.3
• /
• pp.192-196
• /
• 2007

ZnSe/CdSe/ZnSe single quantum wells with different well thickness were grown by hot wall epitaxy. The quantum well thicknesses were measured by TEM. The critical thickness of single quantum well layer was found to be about $9{\AA}$ from the intensities and the full-width at half maximum of photoluminescence(PL) spectra. When the thickness of quantum wells was less than the critical thickness, the Stoke's shift was confirmed from the comparison between PL and photoluminescence excitation spectra, and it may be due to the exciton binding energy. The PL peak energy dependence on the quantum well thickness was coincident with the theoretical values.

• Bulletin of the Korean Chemical Society
• /
• v.27 no.11
• /
• pp.1809-1814
• /
• 2006

The L-Valinate anion coordinating zinc complex, [$Zn(val)_2(H-2O)$], was isolated and structurally characterized by single crystal X-ray crystallography. The crystal possess orthorhombic symmetry with a space group $P2_12_12_1$, Z = 4, and a = 7.4279(2)$\AA$, b = 9.4342(2)$\AA$, c =20.5862(7)$\AA$ respectively. The compound features a penta-coordinate zinc ion in which the two valine anion molecules are directly coordinating the central zinc metal ion via their N (amine) and O (carboxylate) atoms, and an additional coordination to zinc is made by water molecule (solvent) to form a distorted square pyramidal structure. In addition, further synthesis of the valine capped ZnS:Mn nanocrystal from the reaction of [$Zn(val)_2(H-2O)$] precursor with $Na_2S$ and 1.95 weight % of $Mn^{2+}$ dopant is described. Obtained valine capped nanocrystal was water dispersible and was optically characterized by UV-vis and solution PL spectroscopy. The solution PL spectrum for the valine capped ZnS:Mn nanocrystal showed an excitation peak at 280 nm and a very narrow emission peak at 558 nm respectively. The measured and calculated PL efficiency of the nanocrystal in water was 15.8%. The obtained powders were characterized by XRD, HR-TEM, and EDXS analyses. The particle size of the nanocrystal was also measured via a TEM image. The measured average particle size was 3.3 nm.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.02a
• /
• pp.124-124
• /
• 2010

Much interest has been focused on InGaN-based materials and their quantum structures due to their optoelectronics applications such as light emitting diode (LED) and photovoltaic devices, because of its high thermal conductivity, high optical efficiency, and direct wide band gap, in spite of their high density of threading dislocations. Build-in internal field-induced quantum-confined Stark effect in InGaN/GaN quantum well LED structures results in a spatial separation of electrons and holes, which leads to a reduction of radiative recombination rate. Therefore, many growth techniques have been developed by utilizing lateral over-growth mode or by inserting additional layers such as patterned layer and superlattices for reducing threading dislocations and internal fields. In this work, we investigated various characteristics of InGaN multiple quantum wells (MQWs) LED structures grown on selectively wet-etched porous (SWEP) GaN template layer and compared with those grown on non-porous GaN template layer over c-plane sapphire substrates. From the surface morphology measured by atomic force microscope, high resolution X-ray diffraction analysis, low temperature photoluminescence (PL) and PL excitation measurements, good structural and optical properties were observed on both LED structures. However, InGaN MQWs LED structures grown on SWEP GaN template layer show relatively low In composition, thin well width, and blue shift of PL spectra on MQW emission. These results were explained by rough surface of template layer, reduction of residual compressive stress, and less piezoelectric field on MQWs by utilizing SWEP GaN template layer. Better electrical properties were also observed for InGaN MQWs on SWEP GaN template layer, specially at reverse operating condition for I-V measurements.

• Current Photovoltaic Research
• /
• v.4 no.1
• /
• pp.25-29
• /
• 2016

$Eu^{3+}$-activated $MgMoO_4$ phosphor thin films were grown at $400^{\circ}C$ on quartz substrates by radio-frequency magnetron sputter deposition from a 15 mol% Eu-doped $MgMoO_4$ target. After the deposition, the phosphor thin films were annealed at several temperatures for 30 min in air. The influence of thermal annealing temperature on the structural and optical properties of $MgMoO_4:Eu^{3+}$ phosphor thin films was investigated by using X-ray diffraction (XRD), photoluminescence (PL), and ultraviolet-visible spectrophotometry. The transmittance, optical band gap, and intensities of the luminescence and excitation spectra of the thin films were found to depend on the thermal annealing temperature. The XRD patterns indicated that all the thin films had a monoclinic structure with a main (220) diffraction peak. The highest average transmittance of 91.3% in the wavelength range of 320~1100 nm was obtained for the phosphor thin film annealed at $800^{\circ}C$. At this annealing temperature the optical band gap energy was estimated as 4.83 eV. The emission and excitation spectra exhibited that the $MgMoO_4:Eu^{3+}$ phosphor thin films could be effectively excited by near ultraviolet (281 nm) light, and emitted the dominant 614 nm red light. The results show that increasing RTA temperature can enhance $Eu^{3+}$ emission and excitation intensity.

• Korean Journal of Materials Research
• /
• v.20 no.7
• /
• pp.364-369
• /
• 2010

A $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor powder with stuffed tridymite structure was synthesized by glycine-nitrate combustion method. The luminescence, formation process and microstructure of the phosphor powder were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy (PL). The XRD patterns show that the as-synthesized $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor was an amorphous phase. However, a crystalline $SrAl_2O_4 $ phase was formed by calcining at $1200^{\circ}C$ for 4h. From the SEM analysis, also, it was found that the as-synthesized $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor was in irregular porous particles of about 50 ${\mu}m$, while the calcined phosphor was aggregated in spherical particles with radius of about 0.5 ${\mu}m$. The emission spectrum of as-synthesized $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor did not appear, due to the amorphous phase. However, the emission spectrum of the calcined phosphor was observed at 520 nm (2.384eV); it showed green emission peaking, in the range of 450~650 nm. The excitation spectrum of the $SrAl_2O_4:Eu^{2+},Dy^{3+}$ phosphor exhibits a maximum peak intensity at 360 nm (3.44eV) in the range of 250~480 nm. After the removal of the pulse Xe-lamp excitation (360 nm), also, the decay time for the emission spectrum was very slow, which shows the excellent longphosphorescent property of the phosphor, although the decay time decreased exponentially.

• Journal of the Korean Vacuum Society
• /
• v.17 no.1
• /
• pp.34-39
• /
• 2008

We have investigated the characteristics of $Al_{0.55}Ga_{0.45}N$/GaN heterostructures with and without low-temperature (LT) AlN interlayer grown by metalorganic chemical vapor deposition. The structural and optical properties were systematically studied by Rutherford backscattering spectroscopy (RBS), X-ray diffraction (XRD), optical microscopy (OMS), scanning electron microscopy (SEM), and photoluminescence (PL). The Al content (x) of 55% and the structural properties of $Al_xGa_{1-x}N$/GaN heterostructures were investigated by using RBS and XRD, respectively. We carried out OMS and SEM experiments and obtained a decrease of the crack network in $Al_{0.55}Ga_{0.45}N$ layer with LT-AlN interlayer. A two-dimensional electron gas (2DEG)-related PL peak located at ${\sim}3.437eV$ was observed at 10 K for $Al_{0.55}Ga_{0.45}N$/GaN with LT-AlN interlayer. The 2DEG-related emission intensity gradually decreased with increasing temperature and disappeared at temperatures around 100 K. In addition, with increasing the excitation power above 3.0 mW, two 2DEG-related PL peaks were observed at ${\sim}3.411$ and ${\sim}3.437eV$. The observed lower-energy and higher-energy side 2DEG peaks were attributed to the transitions from the sub-band level and the Fermi energy level of 2DEG at the AlGaN/LT-AlN/GaN heterointerface, respectively.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2007.08b
• /
• pp.1551-1554
• /
• 2007

To overcome defect due to large surface of nanoparticle, a redispersible Eu doped $LnPO_4:LnPO_4$ core/shell nanoparticles were prepared in a highboiling coordinating solvent. The particle size of the synthesized core/shell nanophosphors was estimated to be about 8 nm by TEM. In this core/shell nanoparticle, the concentration of Eu ion was optimized on the basis of the emission intensity under UV ray excitation. Also, the PL properties of the nanophosphors have been compared with those of the $LnPO_4:Eu$ nanoparticles.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.15 no.3
• /
• pp.208-213
• /
• 2002

We present the temperature and excitation power density dependence of the photoluminescence from carbon-doped GaAs epilayers grown on GaAs (311)A substrate by atmospheric pressure metalorganic chemical vapor deposition. The measured temperature dependence of the PL peak energy is well expressed by an empirical formula proposed by Varshni. The thermal quenching mechanism of the intensity of 16 K luminescence peak at 1.480 eV is described with the dominant activation energy of 27$\pm$2 meV. The activation energy shows an evidence that the emission band involves the carbon acceptor in the recombination process.