Disorder-Induced Broadband Near-Infrared Persistent and Photostimulated Luminescence in Mg2SnO4:Cr3.

Materials with near-infrared (NIR) persistent luminescence (PersL) and NIR-to-NIR photostimulated luminescence (PSL) properties are attractive platforms for photonic energy harvesting and release. In this work, we develop Mg2SnO4:Cr as a broadband NIR PersL and NIR-to-NIR PSL material (luminescence maxima at ∼800 nm) and reveal the origin of the PersL and PSL properties. The material has an inverse spinel structure with the Mg2+ and Sn4+ disorder at the Wyckoff 16d site based on the Rietveld refinement. Cr K-edge X-ray absorption near-edge structure (XANES) spectra uncover that the doped Cr ions have a +3 valence state and occupy the disordered (Mg,Sn) site with octahedral coordination. The disorder results in multiple Cr3+ centers, and the broadband luminescence originates from the 4T2(4F) → 4A2 transition of Cr3+ at sites with intermediate crystal field strength. The distribution of trap depths is continuous according to the analysis of thermoluminescence (TL) spectra using the initial rising method, which relates to the random distribution of Mg2+ and Sn4+ at the second coordination sphere of the Cr3+ centers rather than the oxygen-related defects. Stimulating the material with a NIR laser, the NIR PersL gets significantly enhanced due to a PSL process. The broadband PersL and PSL are detectable beyond 100 h and have good tissue penetrability and therefore the developed Mg2SnO4:Cr3+ has potential in applications of optical information storage/reading and autofluorescence-free bioimaging. Finally, three crystal and electronic structure factors are proposed for screening new Cr3+-activated PersL and PSL materials.

[Near-infrared luminescence and energy transfer of ACaPO4 : Eu2+, Nd3+ (A = Li, K, Na)].

Near-infrared (NIR) luminescence phosphors ACaPO4 : Eu2+, Nd2+ (A = Li, K, Na) were prepared by conventional solid state method and the sensitization of Nd3+ near-infrared luminescence by Eu2+ was investigated. The characteristic NIR luminescence of Nd3+ in ACaPO4 matrix is greatly enhanced by co-doping of Eu2+. The fluorescence properties of ACaPO4 : Eu2+, the NIR luminescence properties of ACaPO4 : Eu2+, Nd3+ and the fluorescence lifetime were studied. The effect of emission wavelength of Eu2+ on NIR luminescence of Nd3+ was investigated; The energy transfer mechanism between Eu2+ and Nd3+ was also discussed. Emission peak wavelength of Eu2+ In ACaPO4 matrixes was found red shift with the series of A = Li, K, Na and the extent of the overlap with the different excitation peaks of Nd3+ changes obviously. It was concluded that the emission peak position of Eu2+ is a very important factor for energy transfer, and the optimal wavelength range for Eu2+ --> Nd3+ energy transfer is 500 to 550 nm.

[Near-infrared fluorescence and energy transfer in Sr2SiO4 : Eu2+, Nd3+].

Sr2 SiO4 : Eu2+ , Nd3+ was synthesized by solid state synthesis method, and the sensitization of Nd3+ near-infrared luminescence by Eu2+ was investigated. The characteristic near-infrared luminescence of Nd2+ in Sr2 SiO4 matrix was greatly enhanced by co-doping of Eu2+. The mechanism of energy transfer from Eu2+ to Nd3+ was analyzed through investigation of fluorescence excitation and emission spectra, and fluorescence lifetime. Excited Eu2+ (II) transfers energy effectively to Nd3+ through non-radiative energy transfer process in Sr2SiO4, resulting in greatly enhanced near-infrared luminescence of Nd3+, while sensitization of Nd3+ by Eu2+ (I) was achieved by the way of Eu2+ (II).

Synthesis of Y2O2S:Eu3+, Mg2+, Ti4+ hollow microspheres via homogeneous precipitation route.

A phosphorescent material in the form of Y2O2S:Eu3+, Mg2+, Ti4+ hollow microspheres was prepared by homogeneous precipitation using monodispersed carbon spheres as hard templates. Y2O3:Eu3+ hollow microspheres were first synthesized to serve as the precursor. Y2O2S:Eu3+, Mg2+, Ti4+ powders were obtained by calcinating the precursor in a CS2 atmosphere. The crystal structure, morphology and optical properties of the composites were characterized. X-ray diffraction measurements confirmed the purity of the Y2O2S phase. Electron microscopy observations revealed that the Y2O2S:Eu3+, Mg2+, Ti4+ particles inherited the hollow spherical shape from the precursor after being calcined in a CS2 atmosphere and that they had a diameter of 350-450 nm and a wall thickness of about 50-80 nm. After ultraviolet radiation at 265 or 325 nm for 5 min, the particles emitted strong red long-lifetime phosphorescence originating from Eu3+ ions. This phosphorescence is associated with the trapping of charge carriers by Ti4+ and Mg2+ ions.

[PEG assisted hydrothermal synthesis of LaPO4 : Eu3+ nanoparticles].

The present reports a hydrothermal process to synthesize the precursor of Eu(3+)-doped LaPO4 nanoparticles with PEG2000 used as additive. SEM shows that the nanoparticles are similar to spheres. The Eu(3+-)doped LaPO4 phosphor was characterized by powder X-ray diffractometer. According to our measurements with XRD, the products belong to monoclinic monazite type, and the samples were well crystallized after sintering at 700 degrees C for 2 h. The effects of synthesis condition, sintering temperature and time on the luminescence of the samples were investigated. The luminescence data indicated that the optimum condition for synthesizing the precursor was at 180 degrees C for 14 h, and the optimum condition for heat-treatment of the precursor was at 850 degrees C for 1 hour. The effects of different contents of Eu3+ on the luminescence of LaPO4 : EuO3+ nanoparticles were also investigated, and the results showed that the luminescence intensity was enhanced with the slight increase in the Eu3+ content, and the optimum Eu(3+)-doping concentration was 4% (mole fraction).

[Preparation and characterization of long-afterglow nanophosphors CaTiO3 : Pr].

CaTiO3 : Pr nanophosphors were prepared with a gel-network precipitation technique using cheap inorganic precursors. The samples, being well dispersed and sphere-like with an average diameter of 100 nm, were observed with transmission electron microscope (TEM). The mechanism of coprecipitation and crystallization was discussed briefly based on TG-DTA and the X-ray diffractometer (XRD) results. The luminescent properties were investigated by the fluorescence spectrophotometer. The conditions of the preparation process were also studied systematically and the optimal conditions were concluded. The results show that the products with strongest luminescence intensity could be prepared at 1 100 degrees C for one hour, and the luminescent features of samples synthesized by the gel-network precipitation technique are similar to those by solid-state reaction, while the calcining temperature is reduced about 200 degrees C. In conclusion, uniform long-afterglow nanophosphors CaTiO3 : Pr were successfully synthesized with simple apparatus at low cost.

[Hydrothermal preparation and luminescence of LaF3:Ce, Tb nano-sized phosphor].

Green-emitting LaF3:Ce, Tb phosphor nanoparticles were synthesized by a simple hydrothermal method and characterized by XRD, TEM and fluorescence spectra. The prepared samples had a hexagonal shape, fine size (30 nm), and high brightness under ultraviolet, and the structure of LaF3 remained unchanged after being doped with Ce3+ and Tb3+ ions. The blue Ce3+ emission centered at 261 nm is efficiently quenched in the samples of LaF3:Ce, Tb, in which the dominant emission is in the green at 544 nm, originating from the doped Tb3+ ions' transition of (5)D4 to (7)F5. Excitation spectra of the LaF3:Ce, Tb, observed at 544 nm, consist of both contributions from Ce3+ and Tb3+ ions. There is energy transfer of Ce3+ --> Tb3+ in this system. The energy transfer mechanism was discussed. Above all, the phosphor nanoparticles have high photoluminescence intensity even without any calcination, about twice that of bulk materials prepared by high temperature solid synthesis, and the intensity is also stronger than calcined phosphor nanoparticles.

Hydrothermal preparation and luminescence of LaF3:Eu3+ nanoparticles.

LaF3:Eu3+ nanoparticles were prepared by a simple hydrothermal process at low temperature and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and fluorescence spectrum. Well-dispersed nanoparticles with an average size of 30 nm and a hexagonal shape were obtained. The influences of reaction temperature and time on the preparation and luminescence of LaF3:Eu3+ nanoparticles were investigated. Luminescent quenching occurred at a much higher concentration ( approximately 25mol%) and stronger luminescent intensity than in bulk LaF3:Eu3+. Fluorescence intensity of the LaF3:Eu3+ nanoparticles varied remarkably with calcination temperatures. It was found that samples without any further calcinations can emit quite strong fluorescence.

[Synthesis of N'1, N'2-Bis[(1E)-(2-hydroxyphenyl)methylene]- ethanedihydrazide and its application to determination of Zn(II)].

A reagent of N'1,N'2-bis[(1E)-(2-hydroxyphenyl)methylene]ethanedihydrazide (DSOD) was synthesized, and characterized by IR spectra and element analysis. A highly sensitive fluorimetric method for the determination of trace amounts of zinc was proposed based on the reaction of Zn2+ with DSOD in ethanol at pH 7.00. The linear range of the method was 0-65.0 microg x L(-1) with a detection limit of 0.30 microg x L(-1). The interferences of 16 common ions were investigated and the results showed that the DSOD had a good selectivity. The analytical results of detecting trace amounts of Zn2+ in zinc rich salt and hair by this method were satisfactory.

Determination of chlorine in atmosphere by kinetic spectrophotometry.

A kinetic method for determination of chlorine in air was described in the present work. The method based on fading of methyl orange (MO) containing solution in air absorption process. A determination limit of 2.64 microg L(-1) was found. With the present method, chlorine concentration could be determined in several minutes with convenient manipulation. As concentration variation of methyl orange in the absorption solution did not affect the experimental results, fabrication and preservation of the stock absorption is also convenient. The present method is promising in monitoring chlorine concentration in atmosphere.

[Near-infrared luminescence of Yb3+-chrome blue-black R complex].

In the present work, sensitized near-infrared fluorescence from Yb3+-chrome blue-black R (CBR) complex was studied. It was found that Yb3+ forms 1:2 complex with CBR in natural ethanol solution. The visible fluorescence from CBR was quenched when the complex forms, while the near-infrared fluorescence from Yb3+ was greatly enhanced. A mechanism in which CBR absorbs excitation light and transfers its energy to Yb3+ ions was suggested. Near-infrared fluorescence intensity of Yb3+ is proportional to its concentration under the experimental condition, and was not disturbed by the addition of a small amount of other lanthanide ions, which indicate that near-infrared fluorometric analysis should be promising in the determination of single langthanide ions.

[Lanthanide ion luminescence probe: low temperature phase transition of EuS4N complex].

Fluorescence spectrum of EuS4N complex at low temperature is very different from that at room temperature. When temperature changes, shapes of both excitation and emission spectra change dramatically at about 160 K, which is taken as an indicator of the structural change of EuS4N. Peak splitting of 5D0-->7F0 also indicates that there are two different types of coordination structure for Eu3+ ions at low temperature, while only one at room temperature. Thermal effect for the structure transition is also deduced from the relation between fluorescence intensity and temperature changing manner. These results were in good accordance with directly measurement on sample temperature. The reason for the structure change is also discussed from the structure of the EuS4N complex. This study proved that lanthanide luminescent probe, as a complementarity to X-ray diffraction technique, should be an effective tool in low temperature crystal structure study.