RETARDATION OF PHOTOSENSITIZED OXIDATION BY COMPLEX OF HYPOCRELLIN A AND PRASEODYMIUM ION

This paper studies the retardation process for photosensitized oxidation of 9,10-diphenylanthracene(9,10-DPA) induced by hypocrellin A (HA) as a sensitizer in the presence ofpraseodymium ion (Pr~(3 )).Experimental result shows that the prompt fluorescence of HA can be quenched byPr~(3 ) in methanol.Measurement of fluorescence lifetime reveals that it remains constant with increasing con-centration of Pr~(3 ),thus a static quenching character is indicated.The thermally induced delayed fluorescenceof HA can also be quenched effectively by the Pr~(3 )-HA complex.The delayed fluorescence lifetime is re-duced from 1744±50 ns to 700±50 ns and 500±50 ns in the presence of oxygen and Pr~(3 ) respectively,thusthe quenching of delayed fluorescence is of dynamic character.As compared with the double reciprocal rela-tionship of concentration between the oxidation product derived from singlet oxygen and the reactant,it showsthat the Pr~(3 )-HA complex can quench not only the excited triplet of HA but also the singlet oxygen andtherefore the photosensitized oxidation of 9,10-DPA is retarded efficiently.     

STUDIES ON RARE EARTH COMPLEXES WITH CROWN ETHERS ⅩⅧ——Synthesis,Characterization and Crystal Structure of[Sc(NO_3)_3(H_2O)_2]·(15-Crown-5)

The single crystal of the complex [Sc(NO_3)_3(H_2O)_2]·(15C5) has been prepared in acetonitrile.Thenew complex has been characterized by elemental analysis,IR spectra,solubility and molar conductancemeasurements.The structure of the complex is determined by single crystal X-ray diffraction analysis.     

STUDY ON THE SEPARATION AND EXTRACTION MECHANISM OF RARE EARTH ELEMENTS BY MEANS OF REVERSED-PHASE PAPER CHROMATOGRAPHY

Reversed-phase paper chromatography technique is used for study on the extraction mechanism and sep-aration of rare earth elements.As the stationary phase,chromatographic paper strips are impregnated with asolution of monomyristyl phosphoric acid (MPA) in chloroform.Mineral acids are used as developers.The effect of concentration of acids and/or salts upon R_f has been investigated.According to the re-sults of R_f values for a given rare earth element in various acids,the order of extraction ability isHCl>HNO_3>H_2SO_4.A tetrad effect is clearly observed.for the R_f value of rare earth elements.Theeffects of other parameters on the R_f value,such as the quantities of extractant retained by the paper and thetemperature are also examined.Based on the determination of the molar ratio of MPA to rare earth elementsand the number of H~ ions released in extraction reaction,a reasonable mechanism is proposed.The mutualseparation of heavy rare earth elements will be better than that of the light rare earth group because of thelarger separation coefficient of the former.A mixture of Ho-Er-Tm-Lu is successfully separated by thepresent method.     

Samarium doped apatite-type orange-red emitting phosphor Ca_5(PO_4)_2SiO_4 with satisfactory thermal properties for n-UV w-LEDs

A novel single-phase Sm~(3+) activated Ca_5(PO_4)_2SiO_4 phosphor was successfully fabricated via a conventional solid-state method, which can be e fficie ntly excited by near ultraviolet(n-UV) light-emitting chips.The crystal structure and luminescence properties were characterized and analyzed systematically by using relevant instruments. The Ca_5(PO_4)_2SiO_4:Sm~(3+) phosphor shows an orange-red emission peaking at600 nm under the excitation of 403 nm and the optimal doping concentration of Sm~(3+) is determined to be 0.08, The critical distance of Ca_5(PO_4)_2SiO_4:0.08 Sm~(3+) is calculated to be 1.849 nm and concentration quenching mechanism of the Sm~(3+) in Ca_5(PO_4)_2SiO_4 host is ascribed to energy transfer between nearestneighbor activators. The decay time of Ca_5(PO_4)_2 SiO_4: 0,08 Sm~(3+) is determined to be 1.1957 ms. In addition, the effect of temperature on the emission intensity was also studied, 72.4% of the initial intensity is still preserved at 250 ℃, better thermal stability compared to commercial phosphor YAG:Ce~(3+) indicates that Ca_5(PO_4)_2SiO_4:0.08 Sm3+ has excellent thermal stability and active energy is deduced to be 0.130 eV.All the results demonstrate that orange-red emitting Ca_5(PO_4)_2SiO_4:0.08 Sm~(3+) phosphor exhibits good luminescent properties. Owing to the excellent thermal quenching luminescence property,Ca_5(PO4)_2SiO_4:0.08 Sm~(3+) phosphor can be applied in n-UV white light emitting diodes and serve as the warm part of white light.     

Study on Electronic Structure of Rare Earth Complex with Dioxygen

The electronic structure and chemical bonding of[Ce(CO_3)_3O_2]_2~(8-) have been studied by INDO(Intermediate Neglect of Differentiated Overlap)method in this paper.The results obtained show that theHOMO of[Ce(CO_3)_3O_2]_2~(8-) is mainly composed of the anti-bonding π orbitals of the pcroxide ion(O_2~(2-))and the LUMO is mainly composed of the 4f orbitals of the Ce(Ⅳ).The peroxide ion coordinates to ceric ionby means of σ and π dative bonds.After coordination the O-O bond of the peroxide ions is strengthened.Bycomparison with cerous complexes,the contribution of the 4f orbitals to bonding increases in the ceric com-plex.     

Thermal decomposition mechanism of low-content-fluorite Bayan Obo rare earth concentrate roasted with sodium carbonate and its consequent separation study

Thermal decomposition and phase transformation for the mixture of Bayan Obo rare earth concentrate(BORC) and sodium carbonate(Na_2CO_3) roasted at different temperatures with weight ratio of 100:20 were studied in detail in our study.The aim of our study is to reveal the nature of roasting reaction between BORC and Na_2CO_3 and thus providing a new method for processing BORC.The results indicate that BORC can be decomposed completely with Na_2CO_3 at around 600℃ after 3 h.During the calcination process,Ce_(0.5)Nd_(0.5)O_(1.75),NaF,Na_3PO_4,and a rare earth double phosphate phase Na_3RE(PO_4)_2 are formed after the decomposition of BORC with Na_2CO_3.In addition,the thermal decomposition mechanism is determined in the paper.Based on these facts,a clean technique processing BORC was developed.And a CeF_3 powder,whose composition was measured and stability was also evaluated,was obtained for some potential application from the new technique.This research is of significance in terms of the Na_2CO_3-roasting BORC solid reaction study and sheds a light on a potential clean technique for BORC.     

Mechanism of Thermal Decomposition of Rare Earth Acetate Hydrates

The mechanism of thermal decomposition of rare earth acetate hydrates(Ln(Ac)_3·nH_2O,n=5,forLn=La;n=4,for Ln=Pr→Lu,Y,except Pm)has been studied by TG-DTG,DSC,infrared spectra,X-raydiffraction and chemical analysis.The thermal decomposition reaction consists of two stages,one is dehydrationand the other one is decompostion.The final product is oxide.It has been found that the temperature of pro-ducing anhydrous acetates decreases with increasing atomic number of rare earth elements.The activation ener-gies for dehydration and decomposition reaction of rare earth acetate hydrates have been calculated byFreeman-Carroll and Kissinger method.The dependence of activation energy Jor dehydration reaction on theatomic number of rare earth elements shows“inclined‘W’effect”.The enthalpy changes for dehydration anddecomposition reaction have been determined.     

THERMODYNAMIC OPTIMIZATION AND CALCULATION OF THE Fe-Pr SYSTEM

Based on the phase diagram of the Fe-Pr system available,the thermodynamic optimization and calcula-tion of the system have been carried out by the least square method.The lattice stabilities of Fe and Pr aredescribed by the expression recommended by SGTE organization.The liquid phase is described by thesubregular solution model.The intermetallic compounds,Fe_(17)Pr_2 and Fe_2Pr,are treated as stoichiometriccompounds.The optimized parameters describing phases in the system are presented.The comparision be-tween the calculated and experimentally determined phase diagram shows that the agreement is generally verygood except for the liquid δ-Fe equilibrium.It is suggested to measure this part of phase diagram again.     

Preparation and properties of temperature sensitive paint based on Eu(DBM)3phen as probe molecule

Probe molecule Eu(DBM)3 phen is made up of europium oxide(Eu_2 O_3),dibenzoylmethane(DBM) and1,10-phenanthroline(phen). The temperature sensitive paint(TSP) was compounded by the polymerization of the probe molecule, methyl methacrylate(MMA) and the initiator of benzoyl peroxide(BPO).The structure, morphology, luminescence property of probe molecule and the temperature quenching property of the temperature sensitive paint(TSP) were characterized by infrared spectrometer, UV-vis spectrometer, scanning electron microscopy and fluorescence spectrometer respectively. The infrared spectrum and UV-vis spectra show that Eu and DBM form six membered rings, and Eu-O coordinate bonds form. The nanocrystals are in sphere-like morphology with an average size of approximately100 nm. Fluorescence spectra present that the performance of temperature quenching is excellent,what's more, TSP sample has different temperature sensitivity in various temperature scope. Particularly,under excitation of 286 nm, TSP has a highest temperature sensitivity between 50 and 60 ℃, and the strongest fluorescence emission reaches a peak(615 nm). It indicated that probe molecule(Eu(DBM)_3 phen) has strong luminescent intensity and the temperature quenching properties of Eu(DBM)_3 phen/PMMA is good.     

COMPUTER SIMULATION OF STRUCTURE OF La-LaCl_3-KCl MELT

The structure of the La-LaCl_3-KCl molten system at 1223K has been investigated by computersimulation using Monte Carlo method.The partial radial distribution functions of some ion pair as well as thepotential and internal energy of the system at 1223K have been calculated.The results implies that about50% of La(Ⅲ)is six coordinated and LaCl_4~(2-) tetrahedron is the predominant configuration for La(Ⅱ).It is also concluded that the distribution of free space in the molten system is not uniform.There exist manyfissures and empty holes in the molten salt.     

STUDIES ON THE CHROMOPHORIC REACTIONS OF MIXED POLYNUCLEAR COMPLEXES OF RARE EARTH-ARSENAZO Ⅲ-COPPERO-PHENANTHROLINE

In an acidic solution the mixed polynuclear complexes could be formed by association of rareearth-arsenazo Ⅲ complexing anions with copper o-phenanthrolinate cations.In this paper the formationconditions of lanthanum-arsenazo Ⅲ-copper-o-phenanthroline complex and its related reaction mechanismhave been studied in detail.The complex exhibits an absorption maximum at 663 nm and its apparent molarabsorptivity is found to be 1.22×10~5 L·mol~(-1)·cm~(-1).The molar ratio of the components in the complex isestimated to be La:arsenazo Ⅲ:Cu:Phen=1:1:1:3.Its possible molecular formula can expressed as[Cu(Phen)_3](La-arsenazo Ⅲ).The reaction is used to determine micro amounts of lanthanum(or rareearths)in copper containning synthetic samples and satisfactory results are obtained.     

ELECTRONIC STRUCTURE AND BOND CHARACTER OF COMPLEXES OF RARE EARTH CHLORIDES WITH CROWN ETHERS

A series of lanthanide complexes LnCl_3·L(Ln=La,Pr,Nd;L=15-C-5 or 18-C-6)have beensynthesized and their molecular configuration,electronic structure and bond character have been studied byXPS and quantum chemical calculation.The calculated results are in good agreement with that obtained inthe experiments.Three Cl atoms are on the same side of Ln in LnCl_3·15-C-5 and the crown ring on theother side.forming a complex molecule with coordination number 8.LnCl_3·15-C-5 is easily hygroscopic inair because of its unsaturated coordination,which differs sharply from the stable Ln(NO_3)_3·15-C-5 com-plex of coordination number 11.The HOMO and neighboring occupied MOs are composed of Cl 3p and O2p,and the LUMO and neighboring unoccupied MOs are composed of Ln orbitals.The level structure easily pro-duces Ln3d satellite in XPS caused by L→Ln charge transfer transition.Due to the coordination,the absolutevalues of the charge are decreased at Ln and O atoms,but increased at Cl atoms,which is in agreement withXPS results.     

Synthesis and luminescent properties of BaGd2O4:Eu3+ phosphors with highly efficient red-emitting

The BaGd_(2-2 x)Eu_(2 x)O_4(BG, x = 0.01-0.09) phosphors were successfully synthesized via the sol-gel method,and BaY_(2-2 y)Eu_(2 y)O_4(BY, y = 0.005-0.07) phosphors were included for comparison. The pure phase BG phosphors with the ordered CaFe_2 O_4-type structure are obtained by annealing at 1300℃ for5 h. The phosphors with uniform particle size of 120 nm and good dispersion display typical Eu~(3+)emission with the strongest peak at 613 nm(~5 D_0→~7 F_2 transition of Eu3+) under optimal excitation band at 262 nm(CTB band). The presence of Gd~(3+) excitation bands on the PLE spectra monitoring the Eu3+emission directly proves an evidence of Gd~(3+)-Eu~(3+) energy transfer. Owing to the concentration quenching, the optimum content of Eu3+ addition is 5 at%(x = 0.05), and the quenching mechanism is determined to be the exchange reaction between Eu3+. All the BG samples have similar color coordinates and temperature of(0.64 ± 0.02, 0.36 ± 0.01) and 2000 ± 100 K,respectively. The lifetime value of BaGd_(1.9)Eu_(0.1)O_4 for 613 nm is fitted to be 2.19 ± 0.01 ms, and the Eu~(3+) concentration does not change the lifetime significantly. Owing to the Gd~(3+)-Eu~(3+) energy transfer, the luminescent intensity of the BaGd_(1.9)Eu_(0.1)O_4 phosphor is better than BY system. The BG system served as a new type of phosphor is expected to be widely used in lighting and display areas.     

Kinetic Study on the Induced Coordination Reaction of Lanthanum with p-Acetylcarboxylazo

The absorption spectra of p-ACA(p-acetylcarboxylazo)and its complex with lanthanum ionswere determined.The molar ratio of metal to ligand in the complex was estimated to be 1:2.An inductionperiod was found existing in the coordination reaction between La and p-ACA and the effects oftemperature,acidity and ionic strength on the induction period were studied.The reaction mechanism wasdepicted.The rate equation is consistent with the rate law,R=k[La(H_2O)_6~(3+)][H_3O~+],obtained by kineticmethod.Finally the possible geometric structure of this complex was discussed.     

Roles of Ceria on Copper and Manganese Oxides Catalyst——Adsorption of NO and CO

A microreactor system and TPD techniques were used to study the reaction kinetics of the CO+NO reaction and the adsorption of CO,NO,CO_2 and N_2O over Cu-Mn-O(Ⅰ)and Cu-Mn-Ce-O(Ⅱ)catalysts.The results show that the catalytic activity of(Ⅱ)is higher than that of(Ⅰ)for the CO+NO reac-tion,and the higher the conversion of NO,the larger was the activity difference between(Ⅰ)and(Ⅱ).For(Ⅰ)the rate of NO elimination is dependent on the partial pressures of NO,CO,CO_2 with the kinetics or-ders of 0.48,0.56,0.08,respectively.The TPD study shows that the presence of Ce in(Ⅱ)may promote theadsorption of NO,CO on the surface,i.e.an increase of the coverage θ_(NO),θ_(CO),which result in a decrease ofthe hindrance of the reaction products.For CO_2 and N_2O the situation is in the opposite,the presence of Cemakes the θ_(CO)_2)and θ_(NO)on(Ⅱ)decrease,which weakens the inhibition of CO_2 for the reaction.     

Luminescence thermal quenching of M_2SiO_4:Eu~(2+)(M=Sr,Ba) phosphors

In this paper,luminescence thermal quenching of M_2SiO_4:Eu~(2+)(M=Sr,Ba) orthosilicate phosphors and mechanisms for thermal quenching proposed by different authors are briefly reviewed.Depending on preparation conditions and/or Eu~(2+)-doping concentrations,the quenching temperature(T_(1/2)) and activation energy for thermal quenching of the same orthosilicate phosphor reported by different authors are inconsistent.The common conclusion is that T_(1/2) of the intermediate compound(Ba_(1-x)Sr_x)_2 SiO_4:Eu~(2+)(x≈0.5) is higher than that of either Sr_2So_4;Eu~(2+)or Ba_2SiO_4;Eu~(2+)end-member.Moreover,T_(1/2) of the best-performing SrBaSiO_4:Eu~(2+)is evidently lower than that of YAG:Ce~(3+)and some Eu~(2+)-doped nitride phosphors.Rega rding the quenching mechanism,most of the investigators attributed thermal quenching to a thermally assisted 4f-5d cross-over in the configuration coordinate diagram.Only a few authors ascribed thermal quenching to a thermally assisted photoionization of 5 d electron to conduction band of the host.Nonetheless,a close inspection of T_(1/2) and Stokes shift derived from the vibrational spectra of the intermediate compound and end-member phosphors indicates that the 5d electron photo ionization model instead of the 4f-5d crossing decay model should be the genuine mechanism for the thermal quenching of M_2 SiO_4:Eu~(2+)(M=Sr,Ba) phosphors.Since the relationship between T_(1/2) and Stokes shift of the phosphors does not support the 4 f-5 d crossing decay model.The ionization probability of the 5 d electron depends on the energy gap(E_(dC)) between 5 d_1 level of the Eu~(2+)and conduction band minimum(CBM) of the host at higher temperatures.Lattice thermal expansion would result in an elevating 5 d_1 level of the Eu~(2+)along with a diminishing CBM of the host and as a consequence a reduction in E_(dC) and an enhanced photo ionization probability at elevated temperatures.A less rigid lattice and hence a larger coefficient of thermal expansion of M_2SiO_4 hosts should be the physical origin of poorer thermal quenching properties of the orthosilicate phosphors.     

A new resource-rich carbonate luminescent host KNa_5Ca_5(CO_3)_8:A case study activated by Eu~(3+) for red-phosphor purpose

Exploring and designing new luminescent host with rich resource is beneficial to reducing the cost and the large-scale application of luminescent materials.Herein,a series of novel Eu~(3+)-activated KNa_(5-)Ca_5(CO_3)_8 red-emitting phosphors with different Eu~(3+) concentrations were successfully synthesized under mild hydrothermal condition.XRD and SEM characterizations show that all as-prepared KNa_5 Ca_5(CO_3)_8:Eu~(3+) samples crystallize in a hexagonal structure,P63 mc(No.186) space group,and show monodispersed hexagonal sheet mo rphologies,within a side length interval about of 2-3μm and a thickness of about 0.6 μm,Eu~(3+) doping within 6 mol% concentration has little influence on the crystal structure of the host,as indicated by XRD,and FT-IR results,but thermal stability changes as shown by the TG-DTA.KNa_5 Ca_5(CO_3)_8 phosphors with different Eu~(3+) concentrations can emit red-light under effectively excitation by near-UV light.CIE chromaticity coo rdinates of all KNa_5 Ca_5(CO_3)_8:Eu~(3+) phosphors were calculated to locate in red region,and CCT of each sample is the range from 2815 to 3650 K,very close to the tungsten lamp light.Besides,concentration quenching phenomenon appearing at 5 mol% is found to be the result of electric multipolar interaction of Eu3+activators,and the decay lifetime is about1.63 ms,which almost unchanges with Eu~(3+) doping concentration.Importantly,thermal quenching analysis reveals good thermal stability with thermal activation energy of about 0.216 eV.The results reported here demonstrate that KNa_5 Ca_5(CO_3)_8 is a promising fluorescent host for LEDs applications.     

SPECTRAL VARIATION AND CHARACTERISTICS OF LOW VALENCY RARE EARTH IONS IN COMPLEX OXIDESⅢ.EFFECT OF THE CRYSTAL ENVIRONMENT AND CHEMICAL FACTORS ON LUMINESCENCE PROPERTIES OF EUROPIUM (Ⅱ) ION

In this paper,the influence of crystal-field on the Luminescence properties of Eu~(2 ) in complex oxidesare studied theoretically by using purely electrostatic model,the dependence of the 4f~65d levels on Eu-Obond distance is given.Quantum chemistry calculation shows that the splitting extent of 4f~65d energy band incubic or in octahedral fields will be inversely proportional to R~5,where R is the distance of Eu~(2 ) to oxygenligand.The value of R affects slightly the location of the centre of 4f~65d energy band.According to the exper-imental spectrum data,we have discussed the influence of the host chemical composition,the replaced sites ofEu~(2 ) and degree of covalency of Eu-O bond on luminescence properties of Eu~(2 ).Some regularity offluorescence spectrum was observed.In alkali-alkaline earth-phosphates,the splitting extent of 4f~65d band (△E) becomes smaller as theEu-O bond distance (R) increases.In Na_(3-x)(PO_4)_(1-x)(SO_4)_x and Na_(2-x)CaSi_(1-x)P_xO_4 hosts,d-d emissionpeak of Eu~(2 ) will shift to shorter wavelength with the increase of x's value.The crystal structure data show that Eu~(2 ) in K_2Mg_2(SO_4)_3 is affected more strongly by crystal-fieldand covalancy than in KMgF_3,so K_2Mg_2(SO_4)_3:Eu~(2 ) emits blue light (E_(em)~m=400nm) and KMgF_3:Eu~(2 )produces ultraviolet fluorescence.     

Synergetic catalysis of ceria and titania for selective reduction of NO

The promotional effect of the interaction between titania and ceria on the catalytic performance for selective reduction of NO was studied.The catalysts,CeO 2,TiO 2,CeO 2 /TiO 2 and Ti x Ce 1-x O 2,were synthesized and tested in NH 3-Selective catalytic reduction(SCR) of NO,and the samples were characterized by the Brunaller,Emmett and Teller(BET absorbed gas N 2),X-ray diffraction(XRD),high resolution transmission electron microscopy(HR-TEM),and temperature programmed desorption(TPD NH 3) techniques.The improvement mechanism of the interaction between the titania and ceria had been explored and discussed from two aspects of micro-structure and surface acidity.The interaction between the titania and ceria greatly improved the catalytic activity but had little effect on the active temperature.It was first reported that the acid amount determined the catalytic activity and the acid strength determined the active temperature for NH 3-SCR of NO.     

Determination of Compositions and Stability Constants of Holmium and Yttrium Complexes with Tribromoarsenazo by Linear Regression Method

According to the appearing of isosbestic point in the absorption spectra of Ho/Y-Tribromoarsenazo(TBA)systems,the complexation reaction is considered to be M nL=ML_n.A method has been proposed basedon it for calculating the mole fraction of free complexing agent in the solutions from spectral data.and two linearregression formula have been introduced to determine the composition,the molar absorptivity,the conditionalstability constant of the complex and the concentration of the complexing agent.This method has been used in Ho-TBA and Y-TBA systems.Ho~(3 )and Y~(3 )react with TBA and form 1:2 complexes in HCl-NaAc buffer solution at pH 3.80.Their molar absorptivities determined are 1.03×10~8 and1.10×10~8 cm~2·mol~(-1),and the conditional stability constants(logβ_2)are 11.37 and 11.15 respectively.Afterconsidering the pH effect in TBA complexing,their stability constants(log β_2~(ahs))are 43.23 and 43.01.respectively.The new method is adaptable to such systems where the accurate concentration of the complexingagent can not be known conveniently.