Gun Young Hong

Photoluminescence Characteristics of Spherical Y 2 O 3 : Eu Phosphors by Aerosol Pyrolysis

The phosphors of high luminous efficiency for plasma display panel (PDP) applications must have high purity, single phase, uniform particle size, and clean surfaces. Photoluminescence characteristics of europium-doped yttrium oxide phosphors of spherical shape as well as optimum synthetic conditions for maximal luminescence were investigated through emission spectroscopy, X-ray spectroscopy, and scanning electron microscopy. It was found that the spherical Y 2 O 3 :Eu phosphors had good mechanical properties and high emission spectra for device application Optical characteristics of spherical phosphors were mainly dependent on synthetic temperature, doped activator concentrations, particle size, and annealing process. Especially, it was observed that the europium distribution in the host lattice of our samples prepared by aerosol pyrolysis was quite different from that of commercial phosphors by the solid-state reaction method. The resultant spherical phosphors show comparable luminescent properties to the commercial product (product by Nichia Co.) This paper describes the synthetic technique and discusses physical and luminescent properties of spherical phosphors in comparison to the characteristics of phosphors prepared by the solid-state reaction method.

Control of Spectral Properties of Strontium-Alkaline Earth-Silicate-Europium Phosphors for LED Applications

SiO 4 -based phosphors doped by Eu 2 + were studied for use in white light emitting diodes (LEDs). Variations of excitation and emission spectra by changes in the alkaline earth ions in host lattice were studied. It was found that the Sr 2 SiO 4 :Eu -Ba 2 SiO 4 :Eu system was excellent for white LED applications with excitation in the 380-465 nm region. Specially, the yellow light intensity from (Sr,Ba)SiO 4 :Eu was comparable to yttrium aluminum gamet:Ce phosphors for excitation at 465 nm (blue-emitting LED). The peak excitation wavelength could be controlled by the Ba/Sr ratio in the host lattice. Also, it was found that (Sr,Mg)SiO 4 :Eu phosphors efficiently emit blue light at 405 nm excitation.

Spherical BaMgAl10 O 17 : Eu2 + Phosphor Prepared by Aerosol Pyrolysis Technique for PDP Applications

Preparation and luminescent characteristics of blue-emitting BaMgAl 10 O 17 :Eu 2+ (BAM) phosphor with spherical shape for plasma display panel (PDP) application has been investigated by aerosol pyrolysis technique using dissolved nitrates solution. The characteristics of particles were examined by controlling the effects of process conditions on the crystallinity, morphology, and luminescence properties. The as-prepared particles at 1400°C showed smooth surface with spherical shape, but above that temperature, had a rougher surface due to higher crystallization. It reflects that the spherical particles were transformed into the hexagonal form with the preparation temperatures because of structure characteristic of a BAM phosphor. X-ray diffraction measurement indicates that the as-prepared particles above 1600°C had similar crystal structure to that of commercial particles. The crystallinity of the BAM phosphor played a major important factor on the luminescent intensity irrespective of particle shape. Photoluminescent characteristies of particles were compared to those of commercial particles (Nichia Co.) under vacuum ultraviolet excitation.

Improvement of Discharge Characteristics of the Zn2SiO4 : Mn2 + Phosphor Layer in Plasma Display Panels

To improve the discharge characteristics of Zn 2 SiO 4 :Mn 2+ phosphor layers in ac plasma display panels, the charging tendency of phosphor was modified by coating the phosphor surface and manipulating the phosphor paste with metal oxide, and their effects on the driving voltages and addressing time were investigated in terms of the driving conditions of plasma display panel (PDP) cell. It was found that the magnesium oxide, which has a positive charging tendency, was very effective and could dramatically improve the surface characteristics of the phosphor layer for stable discharge of the PDP cell. Consequently, the delay time of addressing current was reduced more than 30% and the minimum values of sustaining voltage as well as addressing voltage could be decreased by 12 V on average, while the luminous efficiency was kept constant and even improved in the case of MgO-coated phosphor.

Enhancement of Luminous Intensity of Spherical Y 2 O 3 : Eu Phosphors Using Flux during Aerosol Pyrolysis

Spherical phosphors of trivalent europium-activated yttrium oxide for flat panel displays were prepared from precursor solutions, which included various fluxes, by aerosol pyrolysis. The effects of the flux on the properties of prepared particles were investigated thoroughly by optical spectroscopy, X-ray spectroscopy, and scanning electron microscopy. To enhance the luminescence intensity of the spherical phosphors, the several fluxes, concentration of each flux, and synthetic temperature were examined and optimized by photoluminescence and cathodoluminescence measurements. The luminescent and physical characteristics of the prepared particles were sensitively influenced by the added flux. Particularly, the spherical phosphors produced from precursors incorporating sodium-based fluxes had relatively higher luminous efficiency. The red emission intensity of the spherical Y 2 O 3 : Eu phosphor was increased by about 30% by the addition of Na 2 HPO 4 compared with the intensity of Y 2 O 3 : Eu alone.

Discharging characteristics of green cell using MgO-Coated Zn2SiO4:Mn2+ phosphor in plasma display panel

The charging tendency of a Zn2SiO4:Mn2+ phosphor surface was modified in order to improve the discharging characteristics of green cell in an ac-plasma display panel (ac-PDP). The zinc silicate (Zn2SiO4:Mn2+) green-emitting phosphor was coated with magnesium oxide (MgO), which has a positive charge on the surface. After fabricating a green cell with MgO-coated Zn2SiO4:Mn2+, the electrical and optical properties were examined. It was found that the dynamic voltage margin could be increased while decreasing address time. This may be ascribed to a change in the charging tendency of Zn2SiO4:Mn2+ phosphor by the MgO coating, which makes stable wall-charge accumulation possible. When Zn2SiO4:Mn2+ phosphor was coated with 1.3 wt% MgO, the address time was decreased to 1.2 µs and the address voltage lowered to 25 V without any misfiring problem, compared with those of a noncoated Zn2SiO4:Mn2+ phosphor layer. The luminescence intensity of the green cell using the MgO-coated phosphor layer was also improved by 10%.

Preparation of Spherical Phosphor ( Y , Gd ) BO 3 : Eu by Polymeric-Aerosol Pyrolysis

The red phosphor of (Y, Gd)BO 3 :Eu 3+ was prepared by aerosol pyrolysis for plasma display panel applications through the polymeric reaction, in which citric acid and ethylene glycol were used as ion carriers, i.e., monomers. This synthetic route was adopted to enhance mechanical and optical characteristics of spherical phosphors. In particular, the phosphors synthesized with monomers showed quite different morphology and luminous efficiency compared to those without monomers. It was certain that polymeric precursor had a good effect on particle formation mechanism and status of particles surface. For enhancing the luminescence intensity and mechanical characteristics, optimal synthesizing conditions were investigated through concentration of monomers, synthesis temperature, and activator concentration. In result. the red emission intensity of the spherical (Y, Gd)BO 3 :Eu 3+ phosphor was increased by about 20% by using the polymeric reaction route, compared to that using conventional spray pyrolysis. They were also observed to have spherical shape. dense morphology, and rigid surface.

Low Voltage Cathodoluminescent Characteristics of Spherical Zinc Aluminogallate Phosphors

In this work, we prepared spherical gallate-hased phosphors using an aerosol pyrolysis method. The synthetic parameters such as post heat-treatment temperature, activator concentration, and degree of reductions were optimized for the maximum cathodoluminescent (CL) intensity. For enhancing the CL luminous efficiency of phosphors, adjustment of lattice structure were also considered. It was found that the CL intensity was sensitive to the crystal structure in host lattice, which would he engineered by Al concentration in ZnGa-Al-O system. The most prominent result on the zinc aluminogallates which are of spherical shape was the brightness of 550 cd/m 2 at 400 V excitation with color coordinate of x x = 0.1665 and y = 0.6655.

Synthesis and Optical Characteristics of Green-Emitting ( Y , Gd ) Al3 ( BO3 ) 4 : Tb3 + Phosphor for Plasma Display Panel Applications

The objective of this work is to find a green phosphor for plasma display panels which has both high luminescence and a short decay time. A new green phosphor, (Y 1-x-y Gd x )Al 3 (BO 3 )4:Tb 3+ y (0.05 S x ≤ 0.5, 0.1 ≤ y ≤ 0.5), was synthesized by a flux-assisted solid reaction and its vacuum UV excitation and emission characteristics were examined. We found that under 147 and 172 nm excitations, (Y 0.3 Gd 0.2 )Al 3 (BO 3 ) 4 :Tb 3+ 0.5 phosphors showed a strong green emission at 535-555 nm corresponding to the electric dipole 5 D 4 → 7 F 5 transition of Tb 3+ . The luminance of (Y 0.3 Gd 0.2 )Al 3 (BO 3 ) 4 :Tb 3+ 0.5 at the 147 nm excitation was higher than that of YBO 3 :Tb 3+ , while the spectrum and decay time of the Tb ion was about the same as that of the commercial phosphor (YBO 3 :Tb 3+ ).

Preparation of Spherical GaN:Zn Phosphors by Aerosol Pyrolysis for FED Applications

For application to field emission displays (FEDs), blue-emitting GaN phosphors doped with Zn ions were prepared by the aerosol pyrolysis technique using ammonia gas. It was found that bulk GaN phase was formed in the gas phase and was well crystallized through the annealing process. The GaN:Zn phosphors synthesized in this work were of about 0.7 μm diam and spherical shape. The emission band was broad and showed a peak near 440 nm, while the excitation peak appeared near 350 nm. The CIE coordinate of the GaN:Zn phosphors was (0.158, 0.122) when they are excited by electron-beam under 5 X 10 - 6 Torr. Cathodoluminescence intensity was sensitive to the postannealing condition, and the doping level of Zn ions was high for maximal luminescence.