Park S.,Silla University |
Vogt T.,University of South Carolina
Journal of Physical Chemistry C | Year: 2010
We show that a family of anion ordered oxyfluorides with the general composition Sr3-xAxMO4F with A = Ca, Ba and 0 ≤ x ≤ 1 and M = Ga1-zAlz and 0 ≤ z ≤ 1, which are promising new host lattices for near-UV excited phosphors with potential use in light-emitting devices, develop defect structures during exposure to reducing gases. These defects in anion-deficient nonstoichiometric (Sr 3-xAx)1-α-2δMO 4-αF1-δ, can be monitored by broad-band photoluminescence emissions centered near 500 nm when excited with 254 nm UV light. We show how the broad-band photoluminescence emissions of these materials respond to synthesis parameters such as temperature, time, and reducing gas flow rate and argue that they could be used to monitor the long-term stability of these phosphors under UV light. Substituting indium into the oxyfluoride lattices we discovered a class of single phase materials with the general formula (Sr3-xBax)1-α-2δAl 1-cIncO4-α F1-δ (x = 0-0.6, c = 0-0.2, and α, δ = 0-0.05) which show self-activating luminescence with an emission maximum near 600 nm when excited in the near-UV region near 400 nm. © 2010 American Chemical Society.
Park S.,Silla University
Journal of Solid State Chemistry | Year: 2012
Luminescent materials composed of Sr 2.5-3x/2Ba 0.5Sm xAl 1-yIn yO 4F (0.001≤x, y≤0.1) were prepared by the solid-state reaction method. After the replacement of Sr 2 and Al 3 ions by Sm 3 and In 3 ions in Sr 2.5Ba 0.5AlO 4F host structure, a novel charge-transfer band centered around 304 nm shifted from 240 nm is monitored; moreover, sharp and well-resolved emission peaks in the 4G 5/2→ 6H J transitions of the Sm 3 activator are observed. The diverse excitation and emission photoluminescence spectra of Sr 2.5-3x/2Ba 0.5Sm xAl 1-yIn yO 4-αF 1-δ (0.001≤x, y≤0.1) phosphors originated by the charge-transfer of the host to the Sm 3 activator, the ff transitions in the Sm 3 ions, and the defect-induced self-activation are also introduced. © 2011 Elsevier Inc.
Cho S.,Silla University
Current Applied Physics | Year: 2010
The nitrogen and aluminium-codoped ZnO (NAZO) thin films are grown by rf magnetron sputtering system with the nitrogen flow ratio changing from 0% to 30%. All of the NAZO films show a strongly c-axis preferred orientation, while the values of the electron concentration are found to decrease with the increase of the nitrogen flow ratio, and they are determined as 1.5-27 × 10 19 cm-3. The optical transmittance spectra indicate an average transmittance of about 95% in the visible range, and a red shift of the band gap energy is observed with increasing the nitrogen flow ratio. These results suggest that the nitrogen flow ratio is an important parameter to grow the high-quality NAZO films for the application of solar cells. © 2010 Elsevier B.V. All rights reserved.
Ahn S.I.,Silla University
Chemical Physics Letters | Year: 2012
The effects of Ag surface plasmons (SPs) on the defects of ZnS are investigated. The photoluminescence (PL) spectra of ZnS on an Ag film show well resolved, enhanced, and red-shifted emissions compared to reference samples. The enhancement of the PL by the Ag layer is attributed to an enhanced energy transfer between overlapping band energies of ZnS by Ag SP. Based on the results, it is suggested that the PL emissions from defects can be enhanced and distinguished by SPs, which provide a direction for the application of SPs to characterize inorganic materials. © 2012 Elsevier B.V. All rights reserved.
Cho S.-W.,Silla University
Bulletin of the Korean Chemical Society | Year: 2013
Red phosphors Ca(1-1.5x)EuxWO4 and Ca(1-2x)EuxNaxWO4 were synthesized with various concentrations x of Eu 3+ ions by using a solid-state reaction method. The crystal structure of the red phosphors were found to be a tetragonal scheelite structure with space group I41/a. X-ray diffraction (XRD) results show the (112) main diffraction peak centered at 2θ = 28.71o, and indicate that there is no basic structural deformation caused by the vacancies VCa″ or the Eu3+ (and Na+) ions in the host crystals. Densities of Ca(1-1.5x)EuxWO4 were measured on a (helium) gas pycnometer. Comparative results between the experimental and theoretical densities reveal that Eu3+ (and Na+) ions replace the Ca2+ ions in the host CaWO4. Also, the photoluminescence (PL) emission and photoluminescence excitation (PLE) spectra show the optical properties of trivalent Eu3+ ions, not of divalent Eu2+. Raman spectra exhibit that, without showing any difference before and after the doping of activators to the host material CaWO4, all the gerade normal modes occur at the identical frequencies with the same shapes and weaker intensities after the substitution. However, the FT-IR spectra show that some of the ungerade normal modes have shifted positions and different shapes, caused by different masses of Eu3+ ions (or Na+ ions, or V Ca″ vacancies) from Ca2+.