In this study, Y3Al5O12:Eu3+ red phosphors were synthesized at different temperatures using a solid state reaction method. The crystal structures, surface and optical properties of the Y3Al5O12:Eu3+ red phosphors were investigated using Xray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and photoluminescence (PL) analyses. From XRD results, the crystal structure of the Y3Al5O12:Eu3+ red phosphors was determined to be cubic. The maximum emission spectra were observed for the Y3Al5O12:Eu3+ red phosphor prepared by annealing for 4h at 1,700 oC. The 565~590 nm photoluminescent spectra of the Y3Al5O12:Eu3+ red phosphors is associated with the 5D0 → 7F2 magnetic dipole transition of the Eu3+ ions. The intensity of the photoluminescent spectra in the red phosphors is more dominant for the magnetic dipole transition than the electric dipole transition with increasing annealing temperature. The International Commission on Illumination (CIE) coordinates of Y3Al5O12:Eu3+ red phosphors prepared by 1,700 oC annealing temperature are X = 0.5994, Y = 0.3647.

Y2O3:Eux (x = 0.005, 0.01, 0.02, 0.03, 0.05, 0.1 mol) phosphors are synthesized with different concentrations of Eu3+ ions by solvothermal method. The crystal structure, surface and optical properties of the Eu doped Y2O3 phosphors are investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and photoluminescence (PL) and photoluminescence excitation (PLE) analyses. From X-ray diffraction (XRD) results, the crystal structure of the Eu doped Y2O3 phosphor is found to be cubic. The maximum emission spectra of the Eu doped Y2O3 phosphors are observed at 0.05 mol Eu3+ concentration. The photoluminescence of 615 nm in the Eu doped Y2O3 phosphors is associated with 5D0 → 7F2 transition of Eu3+ ions. The decrease in emission intensity of 0.1 mol Eu doped Y2O3 is interpreted by concentration quenching. The International Commission on Illumination (CIE) coordinates of 0.05 mol Eu doped Y2O3 phosphor are X = 0.6547, Y = 0.3374.

Lu3Al5-xGaxO12:Ce3+,Cr3+ powders are prepared using a solid-state reaction method. To determine the crystal structure, Rietveld refinement is performed. The results indicate that Ga3+ ions preferentially occupied tetrahedral rather than octahedral sites. The lattice constant linearly increases, obeying Vegard’s law, despite the strong preference of Ga3+ for the tetrahedral sites. Increasing x led to a blue-shift of the Ce3+ emission band in the green region and a change in the emission intensity. Persistent luminescence is observed from the powders prepared with x = 2–3, occurring through a trapping and detrapping process between Ce3+ and Cr3+ ions. The longest persistent luminescence is achieved for x = 2; its lifetime is at least 30 min. The findings are explained using crystal structure refinement, crystal field splitting, optical band gap, and electron trapping mechanism.

SrMoO4:RE3+ (RE=Dy, Sm, Tb, Eu, Dy/Sm) phosphors are prepared by co-precipitation method. The effects of the type and the molar ratio of activator ions on the structural, morphological, and optical properties of the phosphor particles are investigated. X-ray diffraction data reveal that all the phosphors have a tetragonal system with a main (112) diffraction peak. The emission spectra of the SrMoO4 phosphors doped with several activator ions indicate different multicolor emissions: strong yellow-emitting light at 573 nm for Dy3+, red light at 643 nm for Sm3+, green light at 545 nm for Tb3+, and reddish orange light at 614 nm for Eu3+ activator ions. The Dy3+ singly-doped SrMoO4 phosphor shows two dominant emission peaks at 479 and 573 nm corresponding to the 4F9/2→6H15/2 magnetic dipole transition and 4F9/2→6H13/2 electric dipole transition, respectively. For Dy3+ and Sm3+ doubly-doped SrMoO4 phosphors, two kinds of emission peaks are observed. The two emission peaks at 479 and 573 nm are attributed to 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions of Dy3+ and two emission bands centered at 599 and 643 nm are ascribed to 4G5/2→6H7/2 and 4G5/2→6H9/2 transitions of Sm3+. As the concentration of Sm3+ increases from 1 to 5 mol%, the intensities of the emission bands of Dy3+ gradually decrease; those of Sm3+ slowly increase and reach maxima at 5 mol% of Sm3+ ions, and then rapidly decrease with increasing molar ratio of Sm3+ ions due to the concentration quenching effect. Fluorescent security inks based on as-prepared phosphors are synthesized and designed to demonstrate an anticounterfeiting application.

New triple tungstate phosphors NaPbLa(WO4)3:Yb3+/Ho3+ (x = Yb3+/Ho3+ = 7, 8, 9, 10) are successfully fabricated by microwave assisted sol-gel synthesis and their structural and frequency upconversion (UC) characteristics are investigated. The compounds crystallized in the tetragonal space group I41/a and the NaPbLa(WO4)3 host have unit cell parameters a = 5.3927(1) and c = 11.7961(3) Å, V = 343.05(2) Å3, Z = 4. Under excitation at 980 nm, the phosphors have yellowish green emissions, which are derived from the intense 5S2/ 5F4 → 5I8 transitions of Ho3+ ions in the green spectral range and strong 5F5 → 5I8 transitions in the red spectral range. The optimal Yb3+:Ho3+ ratio is revealed to be x = 9, which is attributed to the quenching effect of Ho3+ ions, as indicated by the composition dependence. The UC characteristics are evaluated in detail under consideration of the pump power dependence and Commission Internationale de L'Eclairage chromaticity. The spectroscopic features of Raman spectra are discussed in terms of the superposition of Ho3+ luminescence and vibrational lines. The possibility of controlling the spectral distribution of UC luminescence by the chemical content of tungstate hosts is demonstrated.

Lu(Nb,Ta)O4:Eu3+ powders are synthesized by a solid-state reaction process using LiCl and Li2SO4 fluxes. The photoluminescence (PL) excitation spectra of the synthesized powders consist of broad bands at approximately 270 nm and sharp peaks in the near ultraviolet region, which are assigned to the Nb5+-O2− charge transfer of [NbO4]3− niobates and the f-f transition of Eu3+, respectively. The PL emission spectra exhibit red peaks assigned to the 5D0 → 7FJ transitions of Eu3+. The strongest peak is obtained at 614 nm (5D0 → 7F2), indicating that the Eu3+ ions are incorporated into the Lu3+ asymmetric sites. The addition of fluxes causes the increase in emission intensity, and Li2SO4 flux is more effective for enhancement in emission intensity than is LiCl flux. The substitution of Ta5+ for Nb5+ results in an increase or decrease in the emission intensity of LuNb1-xTaxO4:Eu3+ powders, depending on amount and kind of flux. The findings are explained using particle morphology, modification of the [NbO4]3− structure, formation of substructure of LuTaO4, and change in the crystal field surrounding the Eu3+ ions.

BaSiO3:RE3+ (RE = Sm or Eu) phosphor powders with different concentrations of activator ions are synthesized using the solid-state reaction method. The effects of the concentration of activator ions on the structural, photoluminescent, and morphological properties of the barium silicate phosphors are investigated. X-ray diffraction data reveals that the crystal structure of all the phosphors, regardless of the type and the concentration of the activator ions, is an orthorhombic system with a main (111) diffraction peak. The grain particles agglomerate together to form larger clusters with increasing concentrations of activator ions. The emission spectra of the Sm3+-doped BaSiO3 phosphors under excitation at 406 nm consist of an intense orange band at 604 nm and three weak bands centered at 567, 651, and 711 nm, respectively. As the concentration of Sm3+ increases from 1 to 5 mol%, the intensities of all the emission bands gradually increase, reach maxima at 5 mol% of Sm3+ ions, and then decrease significantly with further increases in the Sm3+ concentration due to the concentration quenching phenomenon. For the Eu3+-doped BaSiO3 phosphors, a strong red emission band at 621 nm and several weak bands are observed. The optimal orange and red light emissions of the BaSiO3 phosphors are obtained when the concentrations of Sm3+ and Eu3+ ions are 5 mol% and 15 mol%, respectively.

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.

LuNbO4:0.2Yb3+,xTm3+ powders were prepared using a solid-state reaction process. The effects of the amount of Tm on up-conversion(UC) and down-conversion(DC) luminescence properties are investigated. X-ray diffraction patterns confirm that Yb3+ and Tm3+ ions are successfully incorporated into Lu sites. Under 980 nm excitation, the UC spectra of the powders predominantly exhibit strong near-infrared emission bands that peak at 805 nm, whereas weak 480 nm emission bands are observed as well. The emission bands are assigned to the 1G4→ 3H6 (480 nm) and 3H4→ 3H6 (805 nm) transitions of the Tm3+ ions via an energy transfer from Yb3+ to Tm3+; two- and three-photon UC processes are responsible for the 805 and 480 nm emissions, respectively. The DC emission spectra exhibit blue emission (1D2→ 3F4) of Tm3+ at 458 nm. The amount of Tm affects the emission intensity with the strongest emissions at x = 0.007 and 0.02 for the UC and DC luminescence, respectively. The results demonstrate that LuNbO4:Yb3+,Tm3+ phosphors are suitable for bio-applications.

A series of CaNb2O6:Dy3+, CaNb2O6:Eu3+ and CaNb2O6:Dy3+, Eu3+ phosphors were prepared by solid-state reaction process. The effects of activator ions on the structural, morphological and optical properties of the phosphor particles were investigated. XRD patterns showed that all the phosphors had an orthorhombic system with a main (131) diffraction peak. For the Dy3+-doped CaNb2O6 phosphor powders, the excitation spectra consisted of one broad band centered at 267 nm in the range of 210-310 nm and three weak peaks; the main emission band showed an intense yellow band at 575 nm that corresponded to the 4F9/2→ 6H13/2 transition of Dy3+ ions. For the Eu3+-doped CaNb2O6 phosphor, the emission spectra under ultraviolet excitation at 263 nm exhibited one strong reddish-orange band centered at 612 nm and four weak bands at 536, 593, 650, and 705 nm. For the Dy3+ and Eu3+-codoped CaNb2O6 phosphor powders, blue and yellow emission bands due to the 4F9/2→ 6H15/2 and 4F9/2→ 6H13/2 transitions of Dy3+ ions and a main reddish-orange emission line at 612 nm resulting from the 5D0→ 7F2 transition of Eu3+ ions were observed. As the concentration of Eu3+ ions increased from 1 mol% to 10 mol%, the intensities of the emissions due to Dy3+ ions rapidly decreased, while those of the emission bands originating from the Eu3+ ions gradually increased, reached maxima at 10 mol%, and then slightly decreased at 15 mol% of Eu3+. These results indicate that white light emission can be achieved by modulating the concentrations of the Eu3+ ions incorporated into the Dy3+-doped CaNb2O6 host lattice.

Ho3+/Yb3+/Tm3+ tri-doped NaY1-x(WO4)2 phosphors with proper doping concentrations of Ho3+, Yb3+ and Tm3+ (x = Ho3+ +Yb3+ +Tm3+, Ho3+ = 0.04, 0.03, 0.02, 0.01, Yb3+ = 0.35, 0.40, 0.45, 0.50 and Tm3+ = 0.01, 0.02, 0.03, 0.04) were successfully synthesized via the microwave sol-gel route, and their upconversion properties were investigated. Well-crystallized microcrystalline particles showed fine and homogeneous microcrystalline morphology with particle sizes of 1-2 μm. The optical properties were comparatively examined using photoluminescence emission and Raman spectroscopy. Under excitation at 980 nm, the doped particles exhibited white emissions based on blue, green and red emission bands, which correspond to the 1G4→ 3H6 transitions of Tm3+ in the blue region, the 5S2/ 5F4→ 5I8 transitions of Ho3+ in the green region, the 5F5→ 5I8 transitions of Ho3+, and the 1G4→ 3F4 and 3H4→ 3H6 transitions of Tm3+ in the red region. The pump power dependence of the upconversion emission intensity and the Commission Internationale de L'Eclairage chromaticity coordinates of the phosphors were evaluated in detail.

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.

To prepare Mn4+-activated K2TiF6 phosphor, a precipitation method without using hydrofluoric acid (HF) was designed. In the synthetic reaction, to prevent the decomposition of K2MnF6, which is used as a source of Mn4+ activator, NH5F2 solution was adopted in place of the HF solution. Single phase K2TiF6:Mn4+ phosphors were successfully synthesized through the designed reaction at room temperature. To acquire high luminance of the phosphor, the reaction conditions such as the type and concentration of the reactants were optimized. Also, the optimum content of Mn4+ activator was evaluator based on the emission intensity. Photoluminescence properties such as excitation and emission spectrum, decay curve, and temperature dependence of PL intensity were investigated. In order to examine the applicability of this material to a white LED, the electroluminescence property of a pc-WLED fabricated by combining the K2TiF6:Mn4+ phosphor with a 450 nm blue-LED chip was measured.

NaCaLa1-x(MoO4)3:Ho3+/Yb3+ ternary molybdates with proper doping concentrations of Ho3+ and Yb3+ (x = Ho3+ +Yb3+, Ho3+ = 0.05 and Yb3+ = 0.35, 0.40, 0.45 and 0.50) were successfully synthesized by microwave sol-gel method. Well-crystallized particles formed after heat-treatment at 900 oC for 16 h showed a fine and homogeneous morphology with particle sizes of 3-5 μm. Under excitation at 980 nm, the UC intensities of the doped samples exhibited strong yellow emissions based on the combination of strong emission bands at 520-nm and 630-nm emission bands in the green and red spectral regions, respectively. The optimal Yb3+:Ho3+ ratios were obtained at 9:1 and 10:1, as indicated by the compositiondependent quenching effect of the Ho3+ ions. The pump power dependence of the upconversion emission intensity and the Commission Internationale de L'Eclairage chromaticity coordinates of the phosphors were evaluated in detail.

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.

CaAl2O4:RE3+(RE = Tb or Dy) phosphor powders were synthesized with different contents of activator ions Tb3+ and Dy3+ by using the solid-state reaction method. The effects of the content of activator ions on the crystal structure, morphology, and emission and excitation properties of the resulting phosphor particles were investigated. XRD patterns showed that all the synthesized phosphors had a monoclinic system with a main (220) diffraction peak, irrespective of the content and type of Tb3+ and Dy3+ ions. For the Tb3+-doped CaAl2O4 phosphor powders, the excitation spectra consisted of one broad band centered at 271 nm in the range of 220-320 nm and several weak peaks; the main emission band showed a strong green band at 552 nm that originated from the 5D4→ 7F5 transition of Tb3+ ions. For the Dy3+-doped CaAl2O4 phosphor, the emission spectra under ultraviolet excitation at 298 nm exhibited one strong yellow band centered at 581 nm and two weak bands at 488 and 672 nm. Concentration-dependent quenching was observed at 0.05 mol of Tb3+ and Dy3+ contents in the CaAl2O4 host lattice.

BaMoO4:Tb3+ phosphor powders were synthesized with different concentrations of Tb3+ ions using the solid-state reaction method. XRD patterns showed that all the phosphors, irrespective of the concentration of Tb3+ ions, had tetragonal systems with two main (112) and (004) diffraction peaks. The excitation spectra of the Tb3+-doped BaMoO4 phosphors consisted of an intense broad band centered at 290 nm in the range of 230-330 nm and two weak bands. The former broad band corresponded to the 4f8 →4f75d1 transition of Tb3+ ions; the latter two weak bands were ascribed to the 7F2→ 5D3 (471 nm) and 7F6→ 5D4 (492 nm) transitions of Tb3+. The main emission band, when excited at 290 nm, showed a strong green band at 550 nm arising from the 5D4→ 7F5 transition of Tb3+ ions. As the concentration of Tb3+ increased from 1 to 10 mol%, the intensities of all the emission lines gradually increased, approached maxima at 10 mol% of Tb3+ ions, and then showed a decreasing tendency with further increase in the Tb3+ ions due to the concentration quenching effect. The critical distance between neighboring Tb3+ ions for concentration quenching was calculated and found to be 12.3 Å, which indicates that dipoledipole interaction was the main mechanism for the concentration quenching of the 5D4→ 7F5 transition of Tb3+ in the BaMoO4:Tb3+ phosphors.

NaLa1-x(MoO4)2:Ho3+/Yb3+ phosphors with the correct doping concentrations of Ho3+ and Yb3+ (x = Ho3++Yb3+, Ho3+ = 0.05 and Yb3+ = 0.35, 0.40, 0.45 and 0.50) were successfully synthesized by the microwave-modified sol-gel method. Well-crystallized particles formed after heat-treatment at 900 oC for 16 h showed a fine and homogeneous morphology with particle sizes of 3-5 μm. The optical properties were examined using photoluminescence emission and Raman spectroscopy. Under excitation at 980 nm, the UC intensities of the doped samples exhibited strong yellow emissions based on the combination of strong emission bands at 545-nm and 655-nm emission bands in green and red spectral regions, respectively. The strong 545-nm emission band in the green region corresponds to the 5S2/5F4→ 5I8 transition in Ho3+ ions, while the strong emission 655-nm band in the red region appears due to the 5F5→ 5I8 transition in Ho3+ ions. Pump power dependence and Commission Internationale de L'Eclairage chromaticity of the upconversion emission intensity were evaluated in detail.

Pb1-xMoO4:Er3+/Yb3+ phosphors with various doping concentrations of Er3+ and Yb3+ (x = Er3++Yb3+, Er3+ = 0.05, 0.1, 0.2, and Yb3+ = 0.2, 0.45) are successfully synthesized using a microwave sol-gel method, and the up-conversion photoluminescence properties are investigated. Well-crystallized particles, which are formed after heat treatment at 900 oC for 16 h, exhibit a fine and homogeneous morphology with particle sizes of 2-5 μm. Under excitation at 980 nm, the Pb0.7MoO4: Er0.1Yb0.2 and Pb0.5MoO4:Er0.05Yb0.45 particles exhibit a strong 525 nm emission band, a weak 550 nm emission band in the green region, and a very weak 655 nm emission band in the red region. The Raman spectra of the doped particles indicate the presence of strong peaks at higher and lower frequencies induced by the disordered structures of Pb1-xMoO4 through the incorporation of the Er3+ and Yb3+ ions into the crystal lattice, which results in the unit cell shrinkage accompanying the new phase formation of the MoO4-x group.