A spherical Sr4Al14O25:Eu2+ phosphor for use in white-light-emitting diodes was synthesized using a liquid-state reaction with two precipitation stages. For the formation of phosphor from a precursor, the calcination temperature was 1,100˚C. The particle morphology of the phosphor was changed by controlling the processing conditions. The synthesized phosphor particles were spherical with a narrow size-distribution and had mono-dispersity. Upon excitation at 395 nm, the phosphor exhibited an emission band centered at 497 nm, corresponding to the 4f65d→4f7 electronic transitions of Eu2+. The critical quenching-concentration of Eu2+ in the synthesized Sr4Al14O25:Eu2+ phosphor was 5 mol%. A phosphor-converted LED was fabricated by the combination of the optimized spherical phosphor and a near-UV 390 nm LED chip. When this pc-LED was operated under various forward-bias currents at room temperature, the pc-LED exhibited a bright blue-green emission band, and high color-stability against changes in input power. Accordingly, the prepared spherical phosphor appears to be an excellent candidate for white LED applications.

Ce3+-doped yttrium aluminum gallium garnet (YAGG:Ce3+), which is a green-emitting phosphor, was synthesizedby solid state reaction using α-phase or γ-phase of nano-sized Al2O3 as the Al source. The processing conditions and thechemical composition of phosphor for the maximum emission intensity were optimized on the basis of emission intensity undervacuum UV excitation. The optimum heating temperature for phosphor preparation was 1550oC. Photoluminescence propertiesof the synthesized phosphor were investigated in detail. From the excitation and emission spectra, it was confirmed that theYAGG:Ce3+ phosphors effectively absorb the vacuum UV of 120-200nm and emit green light positioned around 530nm. Thecrystalline phase of the alumina nanoparticles affected the particle size and the luminescence property of the synthesizedphosphors. Nano-sized γ-Al2O3 was more effective for the achievement of higher emission intensity than was nano-sized α-Al2O3. This discrepancy is considered to be because the diffusion of Al3+ into Y2O3 lattice is dependent on the crystalline phaseof Al2O3, which affects the phase transformation of YAGG:Ce3+ phosphors. The optimum chemical composition, having themaximum emission intensity, was (Y2.98Ce0.02)(Al2.8Ga1.8)O11.4 prepared with γ-Al2O3. On the other hand, the decay time of theYAGG:Ce3+ phosphors, irrespective of the crystalline phase of the nano-sized alumina source, was below 1 ms due to theallowed 5d→4f transition of the Ce3+ activator.

Eu3+ doped YGdO3 phosphors particles which have fine size and narrow size distribution with non aggregated uniform morphology were prepared by solvent evaporation method for the improvement of emission efficiency. Several parameters have been investigated in this study such as the influences of composition ratio of host materials, calcination temperature, amount of activator, surfactant, pH and flux on the photoluminescence intensity, particle size and dispersion. Eu3+ doped YGdO3 phosphor presented a strong narrow band emission peak at 612nm. The maximum emission intensity ofYGdO3:Eu3+ occurred when Eu3+ concentration is 3wt% under vacuum ultra violet excitation. Prepared phosphors were found to have small round-shaped particles about 150nm in size. The addition of PVA as a surfactant inhibits the grain growth and the agglomeration of particles efficiently by reducing the oxygen bridge bonds. As the pH reduces, PL intensity increase due to reducing the formation of oxygen bridge bonds. The particles prepared from solvent evaporation method with 5wt% LiCl were found to have 120% PL intensity compare to particles prepared without LiCl flux.

PDP용 녹색 형광체의 발광특성을 개선시키기 위해 고안된 액상의 화학적 합성법을 사용하여 조성식이 Zn2-x SiO4:xMn(x=0.05, 0.08)인 형광체를 입자크기가 0.5~2μm로 조절하여 제조하였다. 제조된 형광체 입자는 구상이며 잘 분산된 형상을 봉주었고, 고상반응법에 비해 상대적으로 낮은 1080˚C에서 willemite구조의 단일상을 얻을 수 있었다. 또한 진공 자외선 영역의 147 nm의 여기원을 사용하여 광발광 특성을 조사하였다. 입자의 크기가 1μm이고 Mn의 도핑양이 8mole%일 때, 상용 형광체와 비교하여 발광세기는 약 40% 향상되었고 색좌표는 x=0.24, y=0.69로 거의 일치하는 결과를 얻을 수 있었다. 측정된 형광체의 잔광시간은 7.8ms이었다.

폴리 인산염 모체에 이온 반경이 유사한 Sr과 Eu 치환에 적합한 형광체를 찾아 단일 희토류 이온이 첨가 된 형광체를 합성하고 후처리를 통해 형광 영역이 변화를 연구하였다. 고상법을 이용하여 Eu 이온이 첨가 된 NaSr(PO3)3형광체를 합성하고 탄소열환원법을 통하여 NaSr(PO3)3:Eu2+ 형광체를 완성하였다. 두 형광체 모두 X선 회절 측정을 통하여 결정상을 확인하였다. NaSr(PO3)3:Eu3+의 여기 및 방출 스펙트럼 모두 Eu3+ 농도가 증가할수록 형광 강도가 증가하였고 농도소광을 확인하였다. 방출스펙트럼에서 Eu3+ 농도가 높아질 수록 Eu3+ 주변 환경의 국부적 대칭성이 높아지는 것 알 수 있었다. NaSr(PO3)3:Eu2+ 농도별 방출스펙트럼에서 Eu2+ 이온 농도 증가에 따른 Eu2+ 이온 사이의 임계 거리가 가장 가까운 Eu2+ 사이의 에너지 전달에 의해 형광이 감소하는 농도소광의 메커니즘을 확인하였다. 단일 희토류 이온이 첨가된 형광체의 후처리를 통해 형광 영역 변화가 가능하며 형광체 내 Eu3+ 주변 환경의 국부적 대칭성과 Eu2+ 이온간 거리에 따른 에너지 전달 및 농도소광 메커니즘 연구를 통하여 형광 특성 응용에 적합하고 효율성이 높은 형광체 개발에 좋은 모체 결정으로 사용 될 것으로 기대된다.