Ca3MgSi2O8:Eu2+(x = 0.003, 0.005, 0.007, 0.01, 0.03 mol) white phosphors for Light Emitting Diodes(LED) are synthesized with different concentrations of Eu2+ ions using a solid state reaction method. The crystal structures, surface and optical properties of the phosphors are investigated using X-Ray Diffraction(XRD), Scanning Electron Microscope(SEM) and photoluminescence(PL). The X-Ray Diffraction results reveals that the crystal structure of the Ca3MgSi2O8:Eu2+ is a monoclinic system. The particle size of Ca3MgSi2O8:Eu2+ white phosphors is about 1~5 μm, as confirmed by SEM images. The maximum emission spectra of the phosphors are observed at 0.01 mol Eu2+ concentration. The decrease in PL intensity in the Ca3MgSi2O8:Eu2+ white phosphors with Eu2+ concentration is interpreted by concentration quenching. The International Commission on Illumination(CIE) coordinate of 0.01 mol Eu doped Ca3MgSi2O8 is X = 0.2136, Y = 0.3771.

SrAl2O4: Eu2+ and Dy3+ phosphorescent phosphors were synthesized using the polymerized complex method. Generally, phosphorescent phosphors synthesized by conventional solid state reaction show a micro-sized particle diameter; thus, this process is restricted to applications such as phosphorescent ink and paint. However, it is possible to synthesize homogeneous multi-component powders with fine particle diameter by wet process such as the polymerized complex method. The characteristics of SrAl2O4: Eu2+ and Dy3+ powders prepared by polymerized complex method with one and two step calcination processes were comparatively analyzed. Temperatures of organic material removal and crystallization were observed through TG-DTA analysis. The crystalline phase and crystallite size of the SrAl2O4: Eu2+ and Dy3+ phosphorescent phosphors were analyzed by XRD. Microstructures and afterglow characteristics of the SrAl2O4: Eu2+ and Dy3+ phosphors were measured by SEM and spectrofluorometry, respectively.

Eu2+ 이온이 도핑된 질화물 형광체 Sr2Si5N8:Eu2+는 탄소열 환원 질화법 (Carbothermal Reduction Nitridation, CRN)을 이용하여 제조된다. X-선 회절분석기를 이용하여 구조를 관찰할 수 있다. 흡수 밴드 피크인 470 nm 는 Photoluminescence Exitation (PLE) 측정을 통해 확인할 수 있다. 이러한 여기 광은 InGaN 기반으로 한 발광다이오 드에 적용시키기에 효과적일 것으로 기대되며, (Sr1-xEux)2Si5N8:Eu2+ 형광체는 Eu2+ 이온 도핑 농도에 따라 628 nm 부터 670 nm 까지의 피크 파장을 얻을 수 있다. Eu2+의 농도가 증가할수록 발광 파장이 길어지는 적색 편이 현상을 관찰할 수 있다. 청색 발광다이오드에 Y3Al5O12:Ce3+ 형광체와 함께 적용하여 우수한 연색성을 갖는 백색광을 얻을 수 있었다.

본 논문은 Y3Al5O12:Ce3+(YAG:Ce3+) 단결정과 CaAlSiN3:Eu2+(CASN) 형광체에 관하여 연구하였다. 단결정은 floating zone법을 통해 성장시켰다. XRD 측정결과 JCPDS Card(#73-1370)에 상응하며 공간군 la-3d(230)에 속해있고 Cubic 구조로 된 것을 확인할 수 있었다. 단결정의 PL은 550 nm의 발광피크와 반치폭이 71 nm인 넓은 스펙트럼을 나 타냈고 PLE는 350 nm와 460 nm의 피크값을 나타냈다. CASN 분말의 PL은 604 nm, PLE는 460 nm의 피크값을 나타 냈다. CASN을 YAG:Ce3+ 단결정에 코팅하고 blue LED에 적용 후 측정한 결과, 측정한 PL 스펙트럼에서 CASN의 농도 증가에 따라 red shift 현상이 증가함을 알 수 있다. 연색성 또한 YAG:Ce3+ 단결정에서의 Ra는 67, CASN 10 wt%에서 는 78로 개선되는 것을 확인할 수 있었다.

Eu2+/Dy3+-doped Sr2MgSi2O7 powders were synthesized using a solid-state reaction method with flux (NH4Cl). Thebroad photoluminescence (PL) excitation spectra of Sr2MgSi2O7:Eu2+ were assigned to the 4f7-4f65d transition of the Eu2+ ions,showing strong intensities in the range of 375 to 425nm. A single emission band was observed at 470nm, which was the resultof two overlapping subbands at 468 and 507nm owing to Eu(I) and Eu(II) sites. The strongest emission intensity ofSr2MgSi2O7:Eu2+ was obtained at the Eu concentration of 3mol%. This concentration quenching mechanism was attributableto dipole-dipole interaction. The Ba2+ substitution for Sr2+ caused a blue-shift of the emission band; this behavior was discussedby considering the differences in ionic size and covalence between Ba2+ and Sr2+. The effects of the Eu/Dy ratios on thephosphorescence of Sr2MgSi2O7:Eu2+/Dy3+ were investigated by measuring the decay time; the longest afterglow was obtainedfor 0.01Eu2+/0.03Dy3+.

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.

We have synthesized bluish-green, highly-efficient BaSi2O2N2:Eu2+ and (Ba,Sr)Si2O2N2:Eu2+ phosphors through aconventional solid state reaction method using metal carbonate, Si3N4, and Eu2O3 as raw materials. The X-ray diffraction (XRD)pattern of these phosphors revealed that a BaSi2O2N2 single phase was obtained. The excitation and emission spectra showedtypical broadband excitation and emission resulting from the 5d to 4f transition of Eu2+. These phosphors absorb blue light ataround 450nm and emit bluish-green luminescence, with a peak wavelength at around 495 nm. From the results of anexperiment involving Eu concentration quenching, the relative PL intensity was reduced dramatically for Eu=0.033. A smallsubstitution of Sr in place of Ba increased the relative emission intensity of the phosphor. We prepared several white LEDsthrough a combination of BaSi2O2N2:Eu2+, YAG:Ce3+, and silicone resin with a blue InGaN-based LED. In the case of onlythe YAG:Ce3+-converted LED, the color rendering index was 73.4 and the efficiency was 127lm/W. In contrast, in theYAG:Ce3+ and BaSi2O2N2:Eu2+-converted LED, two distinct emission bands from InGaN (450nm) and the two phosphors (475-750nm) are observed, and combine to give a spectrum that appears white to the naked eye. The range of the color renderingindex and the efficiency were 79.7-81.2 and 117-128 lm/W, respectively. The increased values of the color rendering indexindicate that the two phosphor-converted LEDs have improved bluish-green emission compared to the YAG:Ce-converted LED.As such, the BaSi2O2N2:Eu2+ phosphor is applicable to white high-rendered LEDs for solid state lighting.

A SrAl2O4:Eu2+,Dy3+ phosphor powder with stuffed tridymite structure was synthesized by glycine-nitratecombustion method. The luminescence, formation process and microstructure of the phosphor powder were investigated bymeans of X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy (PL). The XRDpatterns show that the as-synthesized SrAl2O4:Eu2+,Dy3+ phosphor was an amorphous phase. However, a crystalline SrAl2O4phase was formed by calcining at 1200oC for 4h. From the SEM analysis, also, it was found that the as-synthesizedSrAl2O4:Eu2+,Dy3+ phosphor was in irregular porous particles of about 50µm, while the calcined phosphor was aggregated inspherical particles with radius of about 0.5µm. The emission spectrum of as-synthesized SrAl2O4:Eu2+,Dy3+ phosphor did notappear, due to the amorphous phase. However, the emission spectrum of the calcined phosphor was observed at 520nm(2.384eV); it showed green emission peaking, in the range of 450~650nm. The excitation spectrum of the SrAl2O4:Eu2+,Dy3+phosphor exhibits a maximum peak intensity at 360nm (3.44eV) in the range of 250~480nm. After the removal of the pulseXe-lamp excitation (360nm), also, the decay time for the emission spectrum was very slow, which shows the excellent long-phosphorescent property of the phosphor, although the decay time decreased exponentially.

Spray pyrolysis was applied to prepare (M=Ca, Sr, Ba) blue phosphor powder. The library of a Ca-Sr-Ba ternary system was obtained by a combinatorial method combined with the spray pyrolysis in order to optimize the luminescent property under vacuum ultraviolet (VUV) excitation. 10 potential compositions were chosen from the first screening. The emission shifted to longer wavelength as Ca became a dominant element and the emission intensity was greatly reduced in the composition region at which Ba is dominant element. On the base of the first screening result, the second fine tuning was carried out in order to optimize the luminescence intensity under VUV excitation. The optimal composition for the highest luminescence intensity was which had the color coordinate of (0.152, 0.072) and about 64% emission intensity of (BAM) phosphor.

In spray pyrolysis, the effects of the preparation temperature, flow rate of the carrier gas and concentration of the spray solution on characteristics such as the morphology, size, and emission intensity of Ca8Mg(SiO4)4Cl2:Eu2+ phosphor powders under long-wavelength ultraviolet light were investigated. The phosphor powders obtained post-treatment had a range of micron sizes with regular morphologies. However, the composition, crystal structure and photoluminescence intensity of the phosphor powders were affected by the preparation conditions of the precursor powders. The Ca8Mg(SiO4)4Cl2:Eu2+ phosphor powders prepared at temperatures that were lower and higher than 700˚C had low photoluminescence intensities due to deficiencies related to the of Cl component. The phosphor powders with the deficient Cl component had impurity peaks of Ca2SiO4. The optimum flow rates of the carrier gas in the preparation of the Ca8Mg(SiO4)4Cl2:Eu2+ phosphor powders with high photoluminescence intensities and regular morphologies were between 40 and 60 l/minute. Phosphor powders prepared from a spray solution above 0.5 M had regular morphologies and high photoluminescence intensities.

The phase transformations and luminescent properties of Eu-doped Ca1-xSrxAl2O4 phosphors were investigated. Ca1-xSrxAl2O4:Eu2+ phosphors were synthesized by a solid-state reaction with a flux, H3BO3. A phase transformation from monoclinic CaAl2O4 to monoclinic SrAl2O4 was observed as the x values increased. A high-temperature hexagonal phase of SrAl2O4 was formed during this transformation as an intermediate phase under an H2 atmosphere due to oxygen vacancies; this did not occur in an air atmosphere. Accordingly, the emission spectra shifted from a blue region to a green region as x increased.

Cu-coated CaS:Eu2+을 1000℃에서 1500℃까지 소성하여 합성하였으며, 이를 스크린 인쇄 방법(screen printing method)을 이용하여 전면 전극층(ITO PET film), 형광층(Cu-coated CaS:Eu2+), 절연층(BaTiO3), 배면 전극층(silver)순으로 적층하였다. 1000℃에서 1500℃까지 소성 온도가 올라감에 따라서 형광체의 grain 크기가 증가 하는 것을 SEM 사진을 통하여 확인하였다. 또한 광 발광(Photoluminescence) 측정에서는 1000℃에서 가장 밝은 발광을 보였으며, 온도가 증가함에 따라 점진적으로 감소하는 경향성을 보였으나, 전계 발광 (Electroluminescence)의 경우에는 1400℃에서 가장 좋은 발광 상태를 보였다. 광 발광과 전계 발광의 경향성 차이는 전계 발광 소자에서의 grain 크기 효과 때문이다. grain 크기가 작아지면 sheet 저항이 낮아지며, 이에 따라 가속되는 전자의 에너지가 증가하여 발광 효율을 높여준 것으로 판단된다.

In recent days, the study of a new phosphorescent phosphor has been performed in order to overcome the defect of sulfide phosphor and increase the brightness and long after-glow characteristic of phosphorescent phosphor. Particularly, sulfide phosphor usually used is so chemically unstable that the study of oxide phosphors are processing. Eu2+, Nd3+ doped Ba-Al-O phosphors sintered at 600~1500℃ for 2hours had the PL emission spectrum and after-glow over 1200℃. In this system, as the mole concentration of alumina increases, emission bands of phosphors moved from 500nm to 380nm. The optimum concentration of flux was 5wt% and after-glow characteristics of phosphors were found at the host material molar ratio (BaCO3:Al2O3), 1:1 and 1:3.