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Qiao, Xuebin,Seo, Hyo Jin Elsevier 2014 JOURNAL OF ALLOYS AND COMPOUNDS Vol.615 No.-
<P><B>Abstract</B></P> <P>This paper reports on the luminescence studies of Eu<SUP>3+</SUP>-doped strontium fluoroapatite. The goal of this paper is to establish and characterize the possible sites for Eu<SUP>3+</SUP> substitution in Sr<SUB>5</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB>F lattice. Eu<SUP>3+</SUP>-doped Sr<SUB>5</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB>F phosphor was prepared by the solid state reaction method. The X-ray powder diffraction result of as-synthesized powder phosphor reveals the single phase Sr<SUB>5</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB>F and it also indicates that the incorporation of Eu<SUP>3+</SUP> ions does not affect the crystal structure. Photoluminescence (PL) studies of Eu<SUP>3+</SUP>-doped Sr<SUB>5</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB>F phosphor are performed to study spectral properties of the sample. Site-selective excitation and emission spectra together with the decay curves are investigated by site-selective laser-excitation spectroscopy. The three crystallographic sites for Eu<SUP>3+</SUP> ions are identified in the <SUP>7</SUP>F<SUB>0</SUB> → <SUP>5</SUP>D<SUB>0</SUB> excitation spectra by using a pulsed, tunable, and narrowband dye laser. The luminescence due to the <SUP>5</SUP>D<SUB>0</SUB> → <SUP>7</SUP>F<I> <SUB>J</SUB> </I> (<I>J</I> =1, 2) transitions under excitation at each crystallographic site exhibits its own spectral features. Three crystallographic sites in Sr<SUB>5</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB>F give rise to different crystal-field splits of the <SUP>7</SUP>F<SUB>1</SUB> and <SUP>7</SUP>F<SUB>2</SUB> multiplets. Heterovalent substitution by rare-earth ions (Eu<SUP>3+</SUP>) for Ca<SUP>2+</SUP> positions in the hexagonal crystal lattice requires charge compensation. The charge-compensation mechanism, site symmetry, and the crystal-field strength on Eu<SUP>3+</SUP> in Sr<SUB>5</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB>F are discussed for better understanding of preferential substitution of Eu<SUP>3+</SUP> in the Sr<SUB>5</SUB>(PO<SUB>4</SUB>)<SUB>3</SUB>F lattice.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Site-selective excitation and emission spectra were investigated. </LI> <LI> The three crystallographic sites for Eu<SUP>3+</SUP> ions were identified. </LI> <LI> Three crystallographic sites give rise to different site symmetry. </LI> <LI> Charge compensation and the crystal-field strength on Eu<SUP>3+</SUP> sites were discussed. </LI> </UL> </P>
Qiao, Xuebin,Huang, Yanlin,Cheng, Han,Seo, Hyo Jin Elsevier 2016 Materials letters Vol.164 No.-
<P><B>Abstract</B></P> <P>A silver vanadate semiconductor K<SUB>2/5</SUB>Ag<SUB>3/5</SUB>VO<SUB>3</SUB> with the stable α-AgVO<SUB>3</SUB> structure has been prepared via the hydrothermal method. The structural refinements were completed. Similar to the well-known β-AgVO<SUB>3</SUB>, K<SUB>2/5</SUB>Ag<SUB>3/5</SUB>VO<SUB>3</SUB> also keeps one-dimensional crystallization habit with a high ratio of length to diameter. The surface was characterized by the SEM, TEM, energy dispersive spectrometer (EDS) spectrum and nitrogen adsorption–desorption isotherms. The UV–vis absorption spectrum shows that K<SUB>2/5</SUB>Ag<SUB>3/5</SUB>VO<SUB>3</SUB> nanowire has narrow band energy (2.02eV) characterized by indirect allowed electronic transition. K<SUB>2/5</SUB>Ag<SUB>3/5</SUB>VO<SUB>3</SUB> nanowires present a very good dispersion in water. Photocatalysis was tested by the photo-degradation of methylene blue (MB) solution. The textile structure of the nanowires makes recovery possible by filtering after photocatalytic reactions<B>.</B> K<SUB>2/5</SUB>Ag<SUB>3/5</SUB>VO<SUB>3</SUB> nanowires show effective photocatalytic ability under visible-light irradiation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> K<SUB>2/5</SUB>Ag<SUB>3/5</SUB>VO<SUB>3</SUB> semiconductor was developed by the hydrothermal method. </LI> <LI> K<SUB>2/5</SUB>Ag<SUB>3/5</SUB>VO<SUB>3</SUB> presents stable α-AgVO<SUB>3</SUB> structure with narrow band (2.02eV). </LI> <LI> It keeps one-dimensional crystallization with a high ratio of length to diameter. </LI> <LI> The nanowires present very good dispersion in water and can be well recycled. </LI> <LI> K<SUB>2/5</SUB>Ag<SUB>3/5</SUB>VO<SUB>3</SUB> has effective photocatalytic ability under visible-light irradiation. </LI> </UL> </P>
Synthesis and luminescence properties of LiMg1-xMnxPO4 solid solutions
Xuebin Qiao 한양대학교 세라믹연구소 2013 Journal of Ceramic Processing Research Vol.14 No.S1
Mn2+-doped LiMg1-xMnxPO4 (x = 0.0035-1) solid solutions were prepared by conventional solid state reaction. A systematic structural of the solid solution series was carried out by X-ray powder diffraction. The emission and excitation spectra were employed to characterize the synthesized phosphors. The XRD results reveal that the samples adopt an olivine (Mg2SiO4) type structure with the space group Pnma. With increasing Mn2+ concentration, the XRD patterns shift systemically to lower angle in indexes of (200), (131), and (211) with all other lines, confirming the formation of solid solutions. The great red-shift of Mn2+ emission with increasing Mn2+-concentration from 0.35 to 100 mol% in LiMg1-xMnxPO4 is observed. The CIE coordinates and the emission shift of Mn2+ ions in LiMg1-xMnxPO4 are discussed in relation to the structural properties of LiMg1-xMnxPO4.
Luminescence properties of novel Ce^3+, Mn^2+ doped NaSr_4(BO_3)_3 phosphors
Xinmin Zhang,Xuebin Qiao,서효진 한국물리학회 2011 Current Applied Physics Vol.11 No.3
A new borate compound NaSr_4(BO_3)_3 doped with Ce^3+, Mn^2+ was prepared by a solid-state reaction at high temperature. The photoluminescence (PL) excitation and emission spectra, low temperature emission spectra and decay curves of Ce^3+, Mn^2+ in NaSr_4(BO_3)_3 were studied. The PL properties of Ce^3+, Mn^2+ co-doped NaSr_4(BO_3)_3 were also investigated. NaSr_4(BO_3)_3:Ce^3+, Mn^2+ phosphors emit two distinctive colors: a blue band centered at 435 nm originating from Ce^3+ and a red band at 660 nm caused by Mn^2+. The results indicate that there exist energy transfer from Ce^3+ to Mn^2+ in the NaSr_4(BO_3)_3 doped with Ce^3+, Mn^2+ system.