Effects of Ce3＋ , Nd3＋ , Gd3＋, Tb3＋ and Lu3＋ ions on Formation of CaCO3

The effects of lanthanides at various concentrations on CaCO3 crystal growth were studied by X-ray diffraction (XRD), infrared spectra (IR), X-ray photoelectric energy spectra (XPS) and inductively coupled plasma mtms spectrometry (ICP-MS). It was found that the calcite, a stable form of CaCO3 in thermodynamics, is the predominant species. The research indicates that lanthanide ions (Ln3 ) can partly substitute the Ca2 in the lattice of CaCO3 crystals, and change the crystal characterization and direct the ordinal growth of CaCO3 crystals.     

Quenching mechanism of Er^3＋ emissions in Er^3＋-and Er^3＋/Yb^3＋-doped SrAl12O19 nanophosphors

Nanoscaled SrAl12O19:Er3+ and SrAl12O19:Yb3+,Er3+ phosphors were synthesized by a combustion method.The emission intensities of every sample were compared by a new method with the emission of codoped Gd3+ ions as a reference.Compared with their bulk material prepared by the solid-state reaction method,a higher Er3+ quenching concentration,as high as 20%,was observed in the nanoscaled phosphors for both visible(VIS) and near infrared(NIR) emissions.The higher quenching concentration in both VIS and NIR regions for nanoscaled samples are related to the structure characteristics of the nano particles.The influence of the introduction of Yb3+ ions on the emission spectra intensity was also investigated and discussed.     

Optical Spectroscopy of Er^3＋ and Er^3＋/Yb^3＋ Co-doped Bi2O3-GeO2-B2O3-ZnO Glasses

The （60 - x）Bi2O3 - xGeO2-30B2O3-10ZnO （x = 5, 10, 20, 30 molar percent） glasses doped with Er^3＋ and Er^3＋/Yb^3＋ were fabricated using the melting method. The thermal stability of the glasses was studied with their DTA curves. The results show that the difference between the glass transition temperature and the crystallization onset temperature increases with the increase of GeO2 content, indicating that the thermal stability of the glass has become better. The absorption spectra were recorded and the stimulated emission cross sections were calculated using the McCumber theory. The Ω2, O4, and Ω6 parameters,the transition probability, the radiative lifetime, and the fluorescence branch ratio of Er^3＋ for optical transition were calculated from their absorption spectra in terms of reduced matrix U^（t）（λ = 2, 4, 6） character for optical transitions. The infrared emission of Er^3＋ was measured upon excitation with 970 nm light and the full width at half-maximum （FWHM） was estimated from the emission spectra. The pumping efficiency and the intensity of the emission at the 1.54 μm band of Er^3＋ were enhanced considerably by co-doping Yb^3＋ .     

Preparation and luminescence properties of Ce3＋/Dy3＋-codoped fluorosilicate glass ceramics

The Ce3+and Dy3+ co-doped fluorosilicate glass and glass ceramics containing SrF2 or CeF3 nanocrystals were prepared under re-ducing atmosphere. The precipitated nano-crystalline phase shifted from cubic SrF2 to hexagonal CeF3 gradually with the heat treatment tem-perature increasing from 620 to 680 °C. The glass and glass ceramics emitted white light, deriving from a combination of the Ce3+ blue and the Dy3+ yellow light. The CIE coordinates could be tuned by adjusting the ratio of Ce3+/Dy3+ concentration. The luminescence could be en-hanced significantly by annealing the samples at the temperatures lower than 640 °C.     

Upconversion Luminescence Properties of Ho^3＋, Tm^3＋, Yb^3＋ Co-Doped Nanocrystal NaYF4 Synthesized by Hydrothermal Method

Nanocrystal of upconversion （UC） phosphor Ho^3＋, Tm^3＋ , and Yb^3＋ co-doped NaYF4 was prepared by the hydrothermal method in the presence of the complexing agent EDTA. Under 980 nm diode laser excitation, the impact of different concentrations of Ho^3＋ ion on the UC luminescence intensity was discussed. The law of luminescence intensity versus pump power shows that the 474 nm blue emission, 538 nm green emission, and 642 nm red emission are all due to the two-photon process, while the 450 nm blue emission is a three-photon process. The UC mechanism and processes were also analyzed. The sample was characterized by transmission electron microscopy （TEM） and X-ray diffraction （XRD）. The result shows that Ho^3＋ ,Tm^3＋ , and Yb^3＋ co-doped NaYF4 prepared by the hydrothermal method exhibits a hexagonal nanocrystal.     

Photon Cascade Emission through Energy Transfer in Pr^3＋and Er^3＋Codoped System

Energy transfer processes in Pr^3 -codoped CaAl12O19crystal from 12 to 290K were studied.Energy transfer from Pr^3 toEr^3 ions in this system was observed,The transfer can partially convert the ^1S0UVfluorescence of Pr^3 into green emission of the characteristic of Er^3 ,The efficiency of the energy transfer was estimated based of the spectroscopic data,The temperature dependence on the transfer was also discussed.     

Biosorption of La^3＋ and Ce^3＋ by Agrobacterium sp.HN1

The Agrobacterium sp.HN1 was isolated from the soil and used to adsorb rare earth ions La3+ and Ce3+.The results showed that the pretreatments of Agrobacterium sp.HN1 did not enhance the adsorption of La3+ and Ce3+.The pH,temperature,time and bacterial age affected the dynamics of adsorption of La3+ and Ce3+.The optimum adsorption conditions for Agrobacterium sp.HN1 were as follows:15 mg/L La3+ of initial concentration,10 mg/L Ce3+,300 mg/L(dry wt.cell) biomass for sorption,6.8 pH,30 oC temperature,150 r/min rotational speed,2 h adsorption time and 28 h bacterial age.The adsorption kinetics of La3+ and Ce3+ for Agrobacterium sp.HN1 followed the pseudo-second order equation.     

Up-conversion of Er3＋/yb3＋ co-doped transparent glass-ceramics containing Ba2LaF7 nanocrystals

The up-conversion of Er3+/Yb3+co-doped transparent glass-ceramics 50SiO2-10AlF3-5TiO2-30BaF2-4LaF3-0.5ErF3-0.5YbF3 containing Ba2 LaF7 nanocrystals under the changing of heat treatment temperature and time were investigated.The Ba2 LaF7 nanocrystals precipitated from the glass matrix was confirmed by X-ray diffraction(XRD).The structural investigation carried out by XRD and transmission electron microscopy(TEM) evidenced the formation of cubic Ba2 LaF7 nanocrystals with crystal size of about 14 nm.Comparing with the samples before heat treatment,the high efficiency up-conversion emission of Er3+/Yb3+co-doped samples was observed in the glass-ceramics under 980 nm laser diode excitation.The increase in red emission intensity bands was stronger than the green bands when the crystal size increased.The mechanism for the up-conversion process in the glass-ceramics and the reasons for the increase of Er3+/Yb3+co-doped up-conversion intensity after heat treatment were discussed.     

Photoluminescence of SrGdGa3O7：RE（RE=Ce^3＋, Pr^3＋ ,Tb^3＋） under VUV-UV Excitation

SrGdGa3O7:RE(RE=Ce^3 ,Pr^3 ,Tb^3 ) were prepared by traditional solid-state reaction and their luminescence properties in the range of VUV-Vis were investigated. The two broad bands situated at about 177 and 217nm in excitation spectra are attributed to the host lattices absorption, and they have no considerable change when doped different rare earth ions. The f-d transitions of Pr^3 and Tb^3 calculated by the formula gathered by Dorenbos were compared to the experimental results. The excitation spectra also show the sharp Gd^3 excitation line at about 274 nm pointing to an efficient energy transfer from Gd^3 to Pr^3 and Tb^3 . All of the emission spectra present the characteristic emissions of rare earth ions when excited by VUV and UV.     

Effect of solvent on luminescence properties of re-dispersible LaF3：Ln3＋ （Ln3＋=Eu3＋, Dy3＋, Sm3＋ and Tb3＋） nanoparticles

LaF3:Ln3+(Eu3+,Dy3+,Sm3+ and Tb3+) nanoparticles were prepared in different solvents such as water,EG(ethylene glycol),DMSO(dimethyl sulfoxide) and their mixed solvents at a relatively low temperature of 150 oC by simple chemical route.All the prepared samples showed hexagonal phase and exhibited spherical morphology.The highest luminescence intensity was observed for the samples prepared in EG than the samples prepared in other solvents.However,the sample prepared in water showed anomalously higher luminescence intensity than that of the sample prepared in DMSO.     

VUV Spectroscopy of GdPO4： Eu^3＋ and GdBO3： Eu^3＋

The emission and the excitation spectra of GdPO4 ： Eu^3＋ and GdBO3： Eu^3 ＋ prepared by solid state reaction method were investigated using the synchrotron radiation source of SUPERLUMI station of HASYLAB. The energy transfer between Gd^3＋ and Eu^3＋ was discussed with the probability of quantum cutting process. In the excitation spectra monitoring the red emission from Eu^3＋ , the distinct lines corresponding to the intraconfigurational 4f-4f transitions from Gd^3＋ were observed for both samples, indicating an efficient energy transfer from host Gd^3＋ ions to the doped Eu^3＋ ions. The efficient energy transfer is necessary for the quantum cutting process based on the two-step energy transfer from Gd^3＋ to Eu^3＋ . However, the overlapping of the lines corresponding to Gd^3＋ ：^8S7/2→^6GJ and the broad excitation band （180 - 270 nm） due to Eu^3＋- O^2- charge transfer states （CTS） around 200 nm cause excitation energy on ^6GJ levels to dissipate into CTS by direct energy transfer, unfavorable to the cross relaxation energy transfer between Gd^3＋ and Eu^3＋, thus unfavorable to the quantum cutting process. With the help of the general rules governing the energy positions of Eu^3＋-O^2- ：CTS, the suggestions concerning searching suitable oxide hosts for Gd^3＋-Eu^3＋ quantum cutting were made.     

Complexation of N＇- [1-（3-aminophenyl）ethylidine] isonicotinohydrazide with La3＋, Pr3＋, Nd3＋, Sm3＋, Eu3＋ and Gd3＋ ions and associated thermodynamics

A novel Schiff base N′-[1-(3-aminophenyl)ethylidine]isonicotinohydrazide was prepared and its complexation behavior towards some selected lanthanides had been studied employing pH-metric and calorimetric titration and spectral techniques. pH-metric studies were carried out for the trivalent La, Pr, Nd, Sm, Eu, and Gd complexes in 30% aqueous-dioxane medium at constant ionic strength of 0.05 mol/L NaClO4 and at different temperatures of 293, 303 and 313 K. The proton-ligand formation constants of the ligand indicated the presence of only one dissociable proton while the metal-ligand formation constants were compatible with the formation of 1:1 Ln(Ⅲ) complexes. The sta-bility of the complexes followed the order: La3+Gd3+, showing a break at gadolinium. The thermodynamic parame-ters, ΔG, ΔH and ΔS associated with protonation and complexation reactions were negative which suggested that all reactions were exother-mic and enthalpy-driven. Isothermal calorimetric studies of Gd3+-aeINH systems at 303 K also showed exothermic nature of the complexation reaction and formation of 1:1 complex in agreement with the pH-metric data. Formation of 1:1 complexes was confirmed by the characteriza-tion of Nd(Ⅲ) complex. A seven coordinated geometry was assigned for the complex based on its elemental and spectral data.     

Luminescence properties of Tm^3＋/Yb^3＋, Er^3＋/Yb^3＋ and Ho^3＋/Yb^3＋ activated calcium tungstate

CaWO4 phosphor activated by the Tm3+/Yb3+,Er3+/Yb3+ and Ho3+/Yb3+ ions were synthesized by a traditional high-temperature solid-state method.The crystal structures and morphologies of the products were characterized by X-ray powders diffraction method(XRD) ,infrared spectra(FT-IR) and scanning electron microscopy(SEM) .The samples were found to show up-conversion luminescence properties.CaWO4 doped with Tm3+/Yb3+ showed blue luminescence characteristic of Tm(III) ion in the range of 460-485 nm,corresponding to the 1G4→3H6 electronic transition.CaWO4 doped with Er3+/Yb3+ showed strong green luminescence at 510-565 nm(2H11/2,4S3/2→4I15/2) and weak red luminescence at 640-685 nm(4F9/2→4I15/2) of Er(III) ion.CaWO4 doped with Ho3+/Yb3+ phosphor emitted green luminescence at 525-560 nm(5S2,5F4→5I8) and red luminescence at 630-670 nm(5F5→5I8) and at 730-770 nm(5S2,5F4→5I7) ,which is the characteristic of Ho(III) ion.     

Energy transfer between Gd^3＋ and Tb^3＋ in phosphate glass

The phosphate glass doped with Gd3+,Tb3+ and Gd3+/Tb3+ were prepared by high temperature melting.The photo-luminescence behavior of Gd3+ and Tb3+ in phosphate glass were investigated by absorption,excitation,and emission spectroscopy.Energy transfer between Gd3+ and Tb3+ in phosphate glass was studied,and it was found that there were two energy transfer mechanisms between Gd3+ and Tb3+ in phosphate glass: one was from 4f7 level of Gd3+ to the 4f8 level of Tb3+,and the other was from 5d level of Tb3+ to 4f7 level of Gd3+.The new findings would be beneficial for the study of Tb3+-doped scintillating phosphate glass.     

Preparation and Long Persistence Red Luminescence of M0.2Ca0.8TiO3 ： Pr^3＋ （M = Mg^2＋ , Sr^2＋ , Ba^2＋ , Zn^2＋）

M0.2Ca0.8TiO3 : Pr^3 (M = Mg^2 , Sr^2 , Ba^2 , Zn^2 ) long persistence red phosphors were prepared by solid state reaction. The influence of the partially replacing Ca^2 in CaTiO3 with Mg^2 , Sr^2 , Ba^2 , Zn^2 on the excitation spectra, the emission spectra and the long persistence properties were studied. The results suggest that certain quantity of Mg^2 , Sr^2 , Ba^2 , Zn^2 which partially replace Ca^2 can enhance the luminescent intensity and prolong the afterglow persistence of the samples. The intensity of Mg0.2Ca0.8TiO3: Pr^3 is above all of the samples. Take Mg0.2Ca0.8TiO3:Pr^3 as the basic sample, the influence of Pr^3 concentrations (C (Pr^3 )) on the long afterglow properties were also studied.The results suggest that when the C (Pr^3 ) is 0.10% (tool fraction) the intensity of the sample is the highest. The excitation spectra of all these samples show broad band spectra ranging from 300 - 500 nm peaking at about 342 nm. The emission spectra also exhibit a broad band peaking at 613 nm (CaTiO3: Pr^3 is 612 nm). XRD research indicates that the crystalline phases change due to the replacement of divalent metal ions. The research on the thermoluminescence spectra of Mg0.2Ca0.8TiO3:Pr^3 indicates that the peak is at 107.35℃ and the depth of the trap energy is about 0.852 eV.     

Upconversion luminescence of Y2O3：Er^3＋ ,Yb^3＋ nanoparticles prepared by a homogeneous precipitation method

Y2O3： Er^3＋, Yb^3＋ nanoparticles were synthesized by a homogeneous precipitation method without and with different concentrations of EDTA 2Na. Upconversion luminescence spectra of the samples were studied under 980 nm laser excitation. The results of XRD showed that the obtained Y2O3：Er^3＋,Yb^3＋ nanoparticles were of a cubic structure. The average crystallite sizes calculated were in the range of 28-40 nm. Green and red upconversion emission were observed, and attributed to ^2H11/2,^4S3/2→^4I15/2 and ^4F9/2→^4I15/2 transitions of the ion, respectively. The ratio of the intensity of green emission to that of red emission drastically changed with a change in the EDTA 2Na concentration. In the sample synthesized without EDTA, the relative intensity of the green emission was weaker than that of the red emission. The relative intensities of green emission increased with the increased amount of EDTA 2Na used. The possible upconversion luminescence mechanisms were discussed.     

Structural and optical studies of Yb^3＋, Er^3＋ and Er^3＋/Yb^3＋ co-doped phosphate glasses

Phosphate glass samples with various Yb2O3 and Er2O3 contents were synthesized by the conventional melt quenching technique and characterized by X-ray diffraction,IR absorption spectroscopy and Raman scattering spectroscopy.The absorption,emission spectra and fluorescence decay studies were carried out both at low and room temperatures.Results showed the existence of several sites occupied by the rare earth ions in the phosphate glass.Up-conversion and cooperative fluorescence were also discussed.     

Energy transfer in Tb~（3＋）,Yb~（3＋） codoped Lu_2O_3 near-infrared downconversion nanophosphors

Tb3+ and Yb3+ codoped Lu2O3 nanophosphors were synthesized by the reverse-strike co-precipitation method. The obtained Lu2O3:Tb3+,Yb3+ nanophosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectra. The XRD results showed that all the prepared nanophosphors could be readily indexed to pure cubic phase of Lu2O3 and indicated good crystallinity. The Tb3+→Yb3+ energy transfer mechanisms in the UV-blue region in Lu2O3 nanophosphors were investigated. The experimental results showed that the strong visible emission around 543 nm from Tb3+ (5D4→7F5) and near-infrared (NIR) emission around 973 nm from Yb3+ (2F5/2→2F7/2) of Lu2O3:Tb3+,Yb3+ nanophosphors were observed under ultraviolet light excitation, respectively. Tb3+ could be effectively excited up to its 4f75d1 state and relaxed down to the 5D4 level, from which the energy was transferred cooperatively to two neighboring Yb3+. The Yb3+ concentration dependent luminescent properties and lifetimes of both the visible and NIR emissions were also studied. The lifetime of the visible emission decreased with the increase of Yb3+ concentration, verifying the efficient energy transfer from the Tb3+ to the Yb3+. Cooperative energy transfer (CET) from Tb3+ to Yb3+ was discussed as a possible mechanism for the near-infrared emission. When doped concentrations were 1 mol.% Tb3+ and 2 mol.% Yb3+, the intensity of NIR emission was the strongest.     

Facile sol-gel combustion synthesis and photoluminescence enhancement of CaZrO3：Sm3＋ nanophosphors via Gd3＋ doping

CaZrO3:Sm and CaZrO3:Sm,Gd nanophosphors were synthesized by a facile and efficient sol-gel combustion method. Their structure and optical properties were studied. The photoluminesce (PL) results showed that the phosphor could be efficiently excited by irradiation at wavelengths in the visible light region (350-430nm). The CaZrO3:Sm nanophosphor exhibited strong yellow-green, orange and red emissions with peak wavelength centered at 565nm (4G5/2→6H5/2), 601nm (4G5/2→6H7/2) and 645nm (4G5/2→6H9/2), respectively. The incorporation of Gd3+ ions could greatly improve the luminescence intensity. The highest emission intensity was observed with 2mol.% Gd3+ doped CaZrO3:3mol.% Sm powder. The material had potential application in the development of materials for LED’s and other optical devices in the visible region.     

Photoluminescent properties of Eu3＋ and Tb3＋ codoped Gd2O3 nanowires and bulk materials

In this paper, the Gd2O3：Eu3＋,Tb3＋phosphors with different doping concentrations of Eu3＋and Tb3＋ions were prepared by a hydrothermal method for nanocrystals and the solid-phase method for microcrystals. The interaction of the doped ions with different concentrations and the luminescent properties of the nanocrystals and microcrystals were studied systematically. Their structure and morphology of Gd2O3：Eu3＋,Tb3＋phosphors were analyzed by means of X-ray powder diffraction （XRD）, transmission electron mi-croscopy （TEM） and scanning electron microscopy （SEM）. The photoluminescence （PL） properties of Gd2O3：Eu3＋,Tb3＋phosphors were also systematically investigated. The results indicated that when the concentration of doped Eu3＋was fixed at 1 mol.%, the emis-sion intensity of Eu3＋ions was degenerating with Tb3＋content increasing, while when the Tb3＋content was fixed at 1 mol.%, the emission intensity of Tb3＋ions reached a maximum when the concentration of Eu3＋was 2 mol.%, implying that the energy transfer from Eu3＋to Tb3＋took place. In addition, Tb3＋could inspire blue-green light and the Eu3＋could inspire red light. Therefore co-doping systems by controlling the doping concentration and the hosts are the potential white emission materials.