Photoluminescent properties of LaF_3:Eu^(3+) and GdF_3:Eu^(3+)nanoparticles prepared by co-precipitation method

GdF3：Eu^3＋ and GdF3：Eu^3＋ nanoparticles were prepared by a co-precipitation method in the presence of the chelating agent, citric acid. The structural properties of the products were characterized by X-ray diffraction （XRD） and transmission electron microscopy （TEM）. The average crystallite size was estimated from the full-width at half-maximum （FWHM） of the diffraction peaks by the Scherrer equation. The sizes of the nanoparticles were 12 nm for LaF3：Eu3＋ and 17 nm for GdF3：Eu^3＋. The luminescent properties of the nanoparticles were investigated by excitation and emission spectra. Energy transfer from Gd3＋ to Eu3＋ was observed.

Spectral analysis in ultraweak emissions of chemi-and electrochemiluminescence systems

Investigation of ultraweak emissions in the processes of chemiluminescence, CL, and electrochemiluminesce, ECL, requires special techniques of their recording and spectral analysis. From among the hitherto proposed methods of detection of the emission spectra of these processes, that of the cut-off filter was most sensitive. The usefulness of this method in interpretation of the CL and ECL systems of the quantum yields in the range 1×10^-9-1×10^-11 containing ions and complexes of Eu（Ⅲ）, Tb（Ⅲ） and Dy0ID was shown. Exceptional character of the emission bands of lanthanide ions, being a result of the f-f electron transitions and in particular their low FWHM, permitted the appli- cation of the cut-off filter method to their analysis. The results obtained for CL and ECL on the basis of analysis of ultraweak emission proved to be successful in analytical applications. The systems containing Eu（Ⅲ） ions hydrated or complexed with organic ligands enabled inferring changes in the coordination sphere of the ions.

Nanosized complex fluorides based on Eu^(3+) doped Sr_2LnF_7(Ln=La, Gd)

A simple co-precipitation approach taking place between Ln3＋, Sr2＋ cations and F anions, led to the formation of nanocrystalline Eu3＋ doped Sr2LnF7 （Ln-La and Gd） complex fluorides. The reaction was carried out in the presence of polyeth- ylene glycol, PEG 6000 as a surfactant/surface modifier, providing small size and homogeneity of the products. The synthesized compounds were composed of small nanoparticles with an average size of 15 nm. All obtained Eu3＋ doped compounds exhibited an intensive red luminescence. In the case of gadolinium based compounds, the energy transfer phenomena could be observed from Gd3＋ ions to Eu3＋ ions. In order to study the structure and morphology of the synthesized fluorides, powder X-ray diffraction （XRD） and transmission electron microscopy （TEM） measurements were performed. Also FT-IR spectra of the products were re- corded, revealing the presence of PEG molecules on the nanoparticles suN＇ace. A spectrofluorometry technique was applied to examine optical properties of the synthesized nanoparticles. Excitation and emission spectra as well as luminescence decay curves were measured and analysed. The performed analysis revealed a red luminescence, typical for the Eu3＋ ion situated in the inorganic, highly symmetric matrix. Concentration quenching phenomena and lifetimes shortening, together with an increasing of the Eu3＋ doping level, were observed and discussed. Judd-Ofelt analysis was also performed for all doped samples, in order to support the registered spectroscopic data and examine in details structural and optoelectronic properties of the synthesized nanomaterials.

Bifunctional luminescent and magnetic core/shell type nanostructures Fe_3O_4@CeF_3:Tb^(3+)/SiO_2

A facile co-precipitation and microemulsion methods were applied to obtain core/shell type nanoparticles. Cerium fluoride doped with terbittrn（Ⅲ） ions supplied intensive green luminescence of the system. Due to the presence of magnetite nanoparticles as cores, the prod- uct was highly sensitive to external magnetic field. Both sorts of nanostructures were encapsulated by silica shell. Such external layer of inert oxide can potentially increase the resistance of prepared nanostructttres to thermal oxidation, aggressive agents, changing ofpH or destructive radiation. Morphology of the product was examined using transmission electron microscopy （TEM）. Formations of the core/shell type nanostructures were clearly seen in the TEM pictures. Powder X-ray diffraction （XRD） confirmed the structure of the products, their nanocrystallinity and amorphous nature of silica shell. Optical properties were investigated by measuring excitation and emission spectra. Such multifunctional luminescent and magnetic nanoparticles coated with easily functionalized silica shell could be applied in many field of science.

Photoluminescence properties of nanosized strontium-yttrium borate phosphor Sr_3Y_2(BO_3) _4:Eu^(3+) obtained by the sol-gel Pechini method

Mixed strontium-yttrium borate phosphor Sr3Y2（BO3）4 doped with Eu^3＋ ions was obtained by the sol-gel Pechini method. Crystal structure of the synthesized compound was analyzed by X-ray powder diffraction. Optimal conditions for the synthesis were found. Photophysical properties of the phosphor samples were investigated by collecting excitation and luminescence spectra as well as measuring lumi- nescence lifetime. Judd-Ofelt analysis showed that Eu^3＋ ions occupied Y^3＋ sites in the crystalline network. The studied compound showed a red emission with the quantum yield of 54%-55% and can be potentially used as phosphor for plasma display panels and luminescent tubes.

Luminescence properties of calcium tungstate activated by lanthanide(Ⅲ) ions

Calcium tungstate phosphors activated by the Ln3＋ ions （Ln-Pr, Nd, Tb, Yb） were synthesized by a traditional high-temperature solid-state method. The crystal structures and morphologies of the products were characterized by scanning electron microscopy （SEM）, X-ray powders diffraction （XRD） and infrared spectra （FT-1R）. The samples were fotmd to show luminescence properties （down-conversion, DC, at excitation wavelength 254 nm and up-conversion, UC, at excitation wavelength 980 nm）. CaWO4 doped with Tb3＋/yb3＋ showed green DC and UC luminescence characteristic of Tb（Ⅲ） ion in the range of 470-660 nm, cor- responding to the 5D4→7F6,5,4,3,2 electronic transition. CaWO4 doped with Pr3＋/Yb3＋ showed week blue, green and red （DC and UC） luminescence of Pr（Ⅲ） ion, in the wavelength region of 450-700 nm. Emission peaks were ascribed to the 3P1→3H4,5,6, 3P0→3H4,5,6, 3P1→3F2 and 3P0→3F2 transitions, respectively. CaWO4 doped with Nd3＋/yb3＋ phosphor emitted orange UC luminescence at 450-690 nm （2p3/2→4I15/2, 4G7/2→419/2,11/2,13/2） and strong near-infrared UC luminescence at 720-900 nm （4F7/2＋4S3/2→4419/2, 4F5/2＋2H3/2→419/2, 4F3/2→4I9/2） which is the characteristic of Nd（Ⅲ） ion.

Spectroscopic properties of Eu^(3+) doped YBO_3 nanophosphors synthesized by modified co-precipitation method

Y1-xEuxBO3 nanophosphors were synthesized by a modified co-precipitation method. The structure of the obtained nanocrystals was determined by X-ray diffraction （XRD） and transmission electron microscopy （TEM）. The average crystallite size was calculated from the full-width at half-maximum （FWHM） of the diffraction peaks by the Scherrer equation. The average particles size was 25±10 nm. The spectroscopic properties of the Y1-xEuxBO3 nanoborates were characterized by excitation and emission spectra under UV and VUV excitation. In order to improve colour purity, the chromaticity coordinates were also calculated.

Structure modeling of terbium doped strontium-lanthanum borate

Terbium doped strontium-lanthanum borate, Sr3La2（BO3）4：Tb （SLB）, was studied by semi-empirical computational ap- proaches using PM6 parametrization and the SPARKLE model for lanthanide（Ⅲ） （Ln（Ⅲ）） cations. The focus of interest was on structural aspects, e.g. the cell parameters and distribution of dopant ions between various sites as a function of dopant concentration. The cell linear dimensions were calculated to decrease linearly with increasing dopant molar concentration. SLB offered two sites for the dopant. Calculations predicted that one of these sites should be preferred by the Tb（Ⅲ） dopant. The optimized cell dimensions as well as the total energies differed for structures with dopant exclusively in site 1 or site 2. Computational predictions were tested against experimental results obtained for SLB synthesized by sol-gel method varying the dopant concentration. The agreement be- tween experimental and computational results was found sufficiently promising to continue the computational studies.

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

CaWO4 phosphor activated by the Tm^3＋/Yb^3＋, Er^3＋/Yb^3＋ and Ho^3＋/Yb^3＋ 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 Tm^3＋/Yb^3＋ showed blue luminescence characteristic of Tm（Ⅲ） ion in the range of 460-485 urn, corresponding to the ^1G4→^3H6 electronic transition. CaWO4 doped with Er^3＋/Yb^3＋ 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 Ho^3＋/Yb^3＋ phosphor emitted green luminescence at 525-560 nm （5S2, 5F4→518） and red luminescence at 6304i70 um （SFs→518） and at 730-770 nm （^5S2, ^5F4→^5I7）, which is the characteristic of Ho（Ⅲ） ion.

An impact of sintering temperature and doping level on structural and spectral properties of Eu-doped strontium aluminium oxide

In the present work, a sol-gel method was employed to prepare nanosized SrAl2O4 powders doped with Eu3＋ions. The raw nano- materials were thermally treated at 900 to 1100℃ for 3 h. The XRD analysis demonstrated that the powders were single-phase nanopowders with high crystallite dispersion. Our studies were focused on relating the luminescence properties of the Eu^3＋ dopant to the NC （nanocrystallites） size. This was achieved by varying the calcinations temperature between 900 and 1100 ℃. The average NC size varied accordingly between -36 and -75 nm. We found that size effect manifested mainly in the expansion of the cell volume and broadening of XRD peaks as indicated by Rietveld analysis. Moreover the emission and excitation spectra, although typical for Eu^3＋ ions, demonstrated some degree of variability with calcinations temperature and doping concentration. To explain these differences a detailed analysis of luminescence spectra by the Judd-Ofelt theory was performed.

Pairs of Ln(Ⅲ)dopant ions in crystalline solid luminophores:an ab initio computational study

Formation of dopant ions clusters in solid （glass） luminophores may affect efficiency of non-radiative energy transfer proc- esses between dopant （photoactivator） ions via shortening of the effective distance between them. This study was based on the as- sumption that the distance between the dopant ions affects the energy of crystal volume at proximity. According to this idea, semi-empirical and ab initio density functional theory （DFT） calculations were performed on various supercells of YVO4：Eu3＋ as a model system. It was noted that a shorter Eu-Eu distance resulted in lower total energy of the system, compared to an analogous structure with distant Eu3＋ ions. As lower energy configurations are preferred, the observed phenomenon was considered to be related to dopant ions clusters formation. Additionally, the values of energies obtained from DFT calculations were used to estimate the per- centage of dopant ions occurring as pairs, for different dopant concentrations. The estimation agreed quite well with the available lit- erature data.