Joung Kyu Park

White light-emitting diodes of GaN-based Sr2SiO4:Eu and the luminescent properties

We have synthesized a Eu2+-activated Sr2SiO4 yellow phosphor and investigated an attempt to develop white light-emitting diodes (LEDs) by combining it with a GaN blue LED chip. Two distinct emission bands from the GaN-based LED and the Sr2SiO4:Eu phosphor are clearly observed at 400 nm and at around 550 nm, respectively. These two emission bands combine to give a spectrum that appears white to the naked eye. Our results showed that GaN (400-nm chip)-based Sr2SiO4:Eu exhibits a better luminous efficiency than that of the industrially available product InGaN (460-nm chip)-based YAG:Ce.

Application of strontium silicate yellow phosphor for white light-emitting diodes

In order to develop a yellow phosphor that emits efficiently under the 450–470 nm excitation range, we have synthesized a Eu2+-activated Sr3SiO5 yellow phosphor and attempted to develop white light-emitting diodes (LEDs) by combining them with a InGaN blue LED chip (460 nm). Two distinct emission bands from the InGaN-based LED and the Sr3SiO5:Eu phosphor are clearly observed at 460 nm and at 570 nm, respectively. These two emission bands combine to give a spectrum that appears white to the naked eye. Our results showed that InGaN (460 nm chip)-based Sr3SiO5:Eu exhibits a better luminous efficiency than that of the industrially available product InGaN (460 nm chip)-based YAG:Ce.

Optical Properties of Eu2 + -Activated Sr2SiO4 Phosphor for Light-Emitting Diodes

We have synthesized a Eu 2 + -activated Sr 2 SiO 4 yellow phosphor and investigated an attempt to develop white light-emitting diodes (LEDs) by combining the phosphor with a GaN blue LED chip. Two distinct emission bands from the GaN-based LED and the Sr 2 SiO 4 :Eu phosphor are clearly observed at 400 nm and at around 550 nm, respectively. These two emission bands combine to give a spectrum that appears white to the naked eye. Also, we investigated the compositional dependence of the luminescence properties of Eu 2 + ions based on the different Mg 2 + contents.

Synthesis of SrTiO3:Al, Pr phosphors from a complex precursor polymer and their luminescent properties

Abstract Red emitting Pr 3+ , Al 3+ doped SrTiO 3 phosphor was synthesized by a polymeric complex method using metallic nitrates, ethylene glycol and citric acid. SrTiO 3 phosphor powder with a large surface area, small particle size and low agglomeration was formed at a low temperature of 600°C. Different particle growth tendency was also observed both above and below 900°C. The luminescent properties of SrTiO 3 :Al, Pr phosphor were investigated by photoluminescence. Under 359xa0nm excitation, SrTiO 3 :Al, Pr phosphor exhibited a strong red emission, peaking at about 620xa0nm. The intensity of the excitation spectra was enhanced by the addition of Al 3+ ions. The luminescence mechanism may be related to the interaction between Pr 3+ and Al 3+ ions. Al 3+ ions absorb the exciting radiation, and this absorbed energy is transferred to the Pr 3+ ions and then emitted from the Pr 3+ ions.

Luminescence Characteristics of Sr3MgSi2 O 8 : Eu Blue Phosphor for Light-Emitting Diodes

We have synthesized a Eu 2 + -activated Sr 3 MgSi 2 O 8 blue phosphor and investigated an attempt to develop blue light-emitting diodes (LEDs) by combining it with an InGaN blue LED chip (λ e m = 405 nm). The InGaN-based Sr 3 MgSi 2 O 8 :Eu LED lamp shows two bands at 405 and 460 nm. The 405 nm emission band is due to a radiative recombination from a InGaN active layer. This 405 nm emission was used as an optical pump for the excitation of the Sr 3 MgSi 2 O 8 :Eu phosphor. The 460 nm emission band is ascribed to a radiative recombination of Eu 2 + impurity ions in the Sr 3 MgSi 2 O 8 host matrix.

Luminescence Properties of Eu2 + -Activated CaAl2Si2 O 8 by Photoluminescence Spectra

We studied the luminescence properties of Eu 2 + in CaAl 2 Si 2 O 8 . In CaAl 2 Si 2 O 8 :Eu 2 + phosphor, two emission bands were observed. Because the two emission bands of CaAl 2 Si 2 O 5 :Eu 2 + phosphor are quite different, it can be presumed that Eu 2 + ions occupy two types of sites, namely, Eu 1 and Eu 2 . The energy transfer between the Eu 2 + ions are elucidated from the critical concentration quenching data based on the electric multipolar interaction of the Eu 1 and Eu 2 sites, respectively. In addition, the dominant multipolar interaction character of the Eu 2 -site emission center was investigated from the relationship between the emission intensity per activator concentration and the activator concentration.

Effect of Li + on the Luminescence Properties of Gd2 O 3 : Eu Phosphor

Eu 3 + -activated Gd 2 - x M x O 3 (M = divalent/monovalent) phosphor was synthesized by a combinatorial polymerized-complex method, which was based on the polymeric complex using citric acid and ethylene glycol. The incorporation of divalent metal ion in Gd 2 O 3 :Eu is not effective for enhancing the Eu 3 + luminescence quantum yield. Co-doping with Li + ion leads to an increase of the quantum yield because Li + substitution in the lattice led to a decrease in interstitial oxygen and hence increase in hole concentration. It is indicated that the decrease in interstitial oxygens led to a decrease in the competitive absorption and hence yielded a higher quantum yield. Also, it can be expected that the Li + ions are introduced into the C 2 site with higher population in the lattice so that the Li + doped Gd 2 O 3 :Eu has a higher quantum yield.

Luminescence Properties of GdOBr:Tb Green Phosphors

Tb 3 + doped gadolinum oxybromide phosphors were synthesized by solid-state reaction. The GdOBr:Tb phosphor showed two intense emission bands, corresponding to 5 D 3 → 7 F 5 and 5 D 4 → 7 F 5 transition with the Tb 3 + concentration. The luminescent properties of GdOBr:Tb phosphor were investigated by photoluminescence. To investigate the multipolar interaction scheme between Tb 3 - ions, the decay behavior was analyzed using direct quenching. The energy interaction type of GdOBr:Tb phosphor was dipole-quadrupole interaction. In addition, the critical distance (R c ) value for energy transfer was calculated by the decay curve fitting parameter from the Inokuti-Hirayama equation. Cathodoluminescent emission spectra were compared with industrially manufactured green phosphors.

Combinatorial synthesis of Tb-activated phosphors in the CaO-Gd2O3-Al2O3 system

A combinatorial polymerized-complex method was adopted in order to search for new Tb 3+ activated green phosphors based on the CaO-Gd 2 O 3 -Al 2 O 3 ternary system. In an attempt to apply newly found phosphors to the plasma display panel, a combinatorial screening was carried out in terms of the photoluminescence (PL) at the vacuum ultraviolet excitation (147 nm). As a result, the optimum composition range was determined as 0.2 < x < 0.25, 0.25 < y < 0.3, and 0.45 < z < 0.5 for Ca x (GdTb) x Al z O δ . We found that the samples in the optimum composition range consist of CaGdAlO 4 , CaGdAl 3 O 7 , and GdAlO 3 phases. The mixed compounds showed a much higher PL efficiency than did any of the constituent compounds.

Effect of Composition on Luminescence Properties of Eu2 + -Activated Mullite

We have studied the photoluminescence properties of Eu 2+ in mullite. The 0.005 mol Eu 2+ -activated Al/Si = 1/2 mullite shows a single broad-band emission character and an emission band at about 435 nm. The emission band shifts slightly to a longer wavelength with an increase in Eu 2+ concentration because the distance between Eu 2+ ions decreases and the probability of energy transfer among Eu 2+ ions increases with increased Eu 2+ concentration. However, Al/Si = 1/1 mullite shows two emission centers, an Eu 1 - and an Eu 2 -site, which peak at 420 and 482 nm. Also, we investigated the compositional dependence of the luminescence properties of the Eu 2+ ions based on the different Al/Si ratios.