Seoung-jae Im

Effects of additional Ce3+ doping on the luminescence of Li2SrSiO4:Eu2+ yellow phosphor

Additional Ce3+ doping improves the luminescence of Li2SrSiO4:Eu2+, a yellow phosphor for ultraviolet or blue light-emitting diodes. By examining the photoluminescence of Li2SrSiO4:Eu2+, Li2SrSiO4:Ce3+, and Li2SrSiO4:Ce3+,Eu2+, it was confirmed that the energy transfer from Ce3+ to Eu2+ ions contributes little to the enhanced luminescence of Li2SrSiO4:Ce3+,Eu2+. Alternatively, we suggested that Ce3+ ions could stabilize the Li vacancies, inhibit the oxidization of Eu2+ to Eu3+, and consequently increase emission intensity, based on the characterizations with decay time and synchrotron light source x-ray absorption measurements. The proposed argument was validated with first principle calculations of the defect formation energies.

Energy Transfer and Brightness Saturation in ( Sr , Ca ) 2P2O7 : Eu2 + , Mn2 + Phosphor for UV-LED Lighting

A red phosphor, (Sr,Ca) 2 P 2 O 7 :Eu 2+ ,Mn 2+ , for UV light-emitting diodes (LEDs) was synthesized under a reducing atmosphere, and its luminescent properties were investigated. The phosphor absorbs UV light at around 400 nm and efficiently emits red light at approximately 610 nm through an energy transfer from Eu 2+ to Mn 2+ . The energy transfer occurs through dipole-quadrupole electric resonance as confirmed by the quantitative estimation of multipolar interactions. Using the varied input current test for the phosphor-loaded LED lamps, it was found that the luminescent efficiency of the phosphor decreased with increasing light flux. This might be due to an increased probability of excited-state absorption and the consequent nonradiative relaxation in Mn 2+ ions, as deduced from a simple analytical model.

Silver silicates with three-dimensional d10-d10 interactions as visible light active photocatalysts for water oxidation

Ag2SiO3 and Ag9(SiO4)2NO3 with the short Ag–Ag bond distances close to metallic Ag have optical band gaps of 2.6 eV and 2.0 eV, respectively. They oxidized water molecules to oxygen with the rates of 98 and 194 μmol/g · h by the 280 mW/cm2 visible-light illumination, and decolorized organic dye more than 10 times faster than the commercialized WO3 and TiO2. Based on the electronic structure calculation, their small band gaps and superior carrier transport property are correlated with the spatial proximity between Ag ions stabilized by d10-d10 interaction, which promotes the descent and dispersion of conduction bands by increasing Ag 5s/5p orbital overlaps.

Melilite-type blue chromophores based on Mn3+ in a trigonal-bipyramidal coordination induced by interstitial oxygen

A new, earth-abundant, environmentally benign, and stable inorganic blue chromophore series Sr2(Mg1−xMnx)Ge2O7+δ has been prepared and characterized by X-ray absorption spectroscopy, synchrotron X-ray diffraction, and ab initio total energy calculation. As the content of Mn in the compound was increased, the color changed from white (for x = 0.0) to sky blue, deep blue, and finally black body color (for x = 1.0). Sr2MgGe2O7 has the melilite-type structure comprising Mg(2+)O4 and GeO4 tetrahedra. On the other hand, it was found that the Mn ion in Sr2(Mg1−xMnx)Ge2O7+δ is mainly trivalent and that the additional oxygen atom infiltrates into the lattice to compensate for the excess positive charge. The additional oxygen atom occupies an interstitial site, leading to the formation of Mn(3+)O5 trigonal bipyramid and Ge(4+)O5 square pyramid. As the driving force for the Mn(3+)O5 formation, the tendency for improving the lattice coherency between BO4–B′O4 and AO8 layers in the melilite A2BB′2O7 is suggested.

P-50: Excimer Gas Discharge Characteristics for Color AC-PDPs

We present the discharge characteristics of a rare gas halide mixture in AC- Plasma Display Panels. Studies for excimer gas of plasma display panels are performed using XeF. This excimer gas is investigated as function of its pressure and different discharge condition. In this paper, the real panel using XeF excimer gas is researched for good discharge characteristics and a full-color panel is demonstrated.

25.3: Luminous Efficacy Dependence of Kr2* Excimer ACPDP on Sustain Driving Conditions

Sustain driving conditions for Kr2* excimer ACPDP are investigated with real 6-inch panels. At the optimized driving with 5 kHz, the PDP with a mixture of Kr: Ne = 50:50 (%) shows the efficacy of 1.6 lm/W, which is over 2 times higher than that of the same PDP panel with a conventional mixture (Xe: Ne = 4:96 (%), 0.7 lm/W).

Effect of Alkali-Earth Metal Fluorides on Phase and Luminescence of Magnesium Germanate Phosphors

The luminescence intensity of 3.5MgO · 0.5 MgF 2 · Geo 2 :Mn 4+ was enhanced by 143, 141, and 149% when MgF 2 was replaced with CaF 2 , SrF 2 , and BaF 2 , respectively. MgF 2 contributes to the enhancement of the phosphor crystallinity by inserting F- into the structure and by decreasing the phase formation temperature. Because CaF 2 , SrF 2 , and BaF 2 not only supply F - to the host but also function as fluxes, they can improve the crystallinity more effectively than MgF 2 . A light emitting diode (LED) lamp with 3.5MgO · 0.5SrF 2 . GeO 2 :Mn 4+ and Y 3 Al 5 O 12 :Ce 3+ (YAG) shows a stable performance for various forward currents and higher color rendering index than that observed in a conventional YAG-based white LED lamp.

40.1: Invited Paper: The Dual Coplanar Electrode Mercury Free Flat Fluorescent Lamp

The authors introduce a dual coplanar electrode flat fluorescent lamp, which is basically the sum of two coplanar electrode lamps, one having the electrodes on the front plate and the other on the bottom plate. It has the same level of discharge stability as that in a usual coplanar lamp. And the results also indicate that the brightness and luminous efficacy improve largely for a dual coplanar lamp compared to a coplanar lamp because there is less diffusion loss for the dual coplanar lamp.

Luminous efficacy evaluation of XeI excimer for ACPDP

We demonstrate for the first time a luminous efficacy of a Xel excimer PDP comparable to that of a conventional Xe/Ne-mixture PDP using 6-in. ACPDPs. For the conventional PDP as a reference, a mixture of Xe:Ne = 4:96(%) with a total gas pressure of 60.0 kPa (450 torr) was used. For the Xel PDP, Ne-buffered mixtures with the same total gas pressure were tried, and a mixture of I 2 :Xe:Ne = 0.02:7.1:92.88 (%) showed an efficacy as high as that of the conventional Xe PDP.

P-62: Dielectric Material Properties of CaF2 for AC PDPs

We present the discharge characteristics of new dielectric layers in AC- plasma display panels. Studies for dielectric layer of plasma display panels are performed using CaF2. In this paper, the real panel using CaF2 dielectric layer is researched for material characteristics and discharge characteristics, and a color panel is demonstrated.