[Show abstract][Hide abstract] ABSTRACT: Yttrium-gadolinium aluminum garnets (YGdAG) doped with Ce3+ ions have been prepared by co-precipitation method. The luminescent properties of Ce3+ ions in Gd3(1−x)Ce3xAl5O12 (х = 0.01) have been studied upon excitation in the 2–20 eV region. The substitution of Gd3+ for Y3+ in the garnet structure results in broadening the emission band and shifting its maximum towards the longer wavelengths. It was found that in addition to the 4f → 5d excitation bands of Ce3+ ions, the excitation spectra for the Ce3+ emission contain bands at 6.67, 7.75, and 9.76 eV. These bands are attributed to the Ce3+-bound exciton formation and O 2p → Al 3s, 3p transitions, respectively. Although gadolinium states dominate near the bottom of the conduction band of Gd3Al5O12, contributions from Altetr and Aloct atoms to the conduction-band density of states are evaluated as quite essential.
Materials Research Bulletin 04/2015; 64. DOI:10.1016/j.materresbull.2014.12.056 · 2.29 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Luminescence spectroscopy has been used to determine the parameters of NaI-SrI2-Eu, NaI-SrCl2-Eu, and NaI-BaI2-Eu compounds in the energy range of 3.7-18 eV at 10 and 295 K and investigate the phase formation in these crystalline systems. The NaI-SrI2(1 mol %)-Eu(0.02 mol %) crystalline system has revealed formation of SrI2 microcrystals activated with europium ions and dispersed in the NaI matrix. Formation of SrCl2-Eu2+ microcrystals dispersed in a NaI matrix is observed for NaI-SrCl2(1 mol %)-Eu(0.02 mol %) crystalline system. The mechanisms of aggregation of impurity ions and specific features of luminescence excitation for europium ions in dispersed microcrystals are discussed.
Optics and Spectroscopy 10/2014; 117(4):593-597. DOI:10.1134/S0030400X14090215 · 0.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Possible reasons for essential differences in values of the total crystal field splitting and centroid shift of Ce3+ 5d configuration for isostructural Li2CaGeO4 and Li2CaSiO4 were analyzed by means of X-ray diffraction method and luminescent spectroscopy. It was found that the increase in Si concentration in Ce3+-doped Li2CaGe1-xSixO4 solid solutions leads to increasing of noncubic crystal field splitting parameter (Delta) of the Ce3+ 5d configuration, indicating to an enhancement of distortion from the cubic symmetry of the calcium dodecahedral site upon going from Li2CaGeO4 to Li2CaSiO4. The results of X-ray diffraction analysis of Li2CaGe1-xSixO4 show that the linear decrease of the unit-cell parameters with increasing Si-content is followed by complex changes in the geometry of the Ca polyhedra. Changes in the electronic structure with the composition of the solid solutions are also discussed.
Journal of Luminescence 10/2014; 154:496-501. DOI:10.1016/j.jlumin.2014.05.034 · 2.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The spectral characteristics of BaF2 and BaF2:Tm crystals and ceramics are compared. The vacuum UV (VUV) and UV absorption spectra and excitation spectra of core-valence and exciton luminescence are investigated. The main exciton and electron-hole processes responsible for the structure of recorded spectra are considered.
Optics and Spectroscopy 09/2014; 117(3):392-395. DOI:10.1134/S0030400X14090227 · 0.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The dependence of X-ray excited luminescence intensity on BaF2 nanoparticle size was studied. A sharp decrease of self-trapped exciton luminescence intensity was observed when the nanoparticle size is less than 80 nm. The main mechanism of the luminescence quenching is caused by the escape of electrons from the nanoparticles. Escape of electrons from nanoparticles is confirmed by the considerable increase of luminescence intensity of the polystyrene scintillator with embedded BaF2 nanoparticles comparing with pure polystyrene scintillator.
[Show abstract][Hide abstract] ABSTRACT: The present research was carried out in order to elucidate the mechanisms of energy transfer from the crystal lattice to Pr3+ ions in SrCl2. The luminescence excitation and emission spectra as well as luminescence kinetics of the SrCl2:Pr single crystals containing 0.2 mol% Pr were investigated at 300 and 10 K using the vacuum ultraviolet (VUV) synchrotron radiation. The X-ray excited luminescence spectra of the SrCl2:Pr (C-Pr=0.2 and 0.5 mol%) and SrCl2:Pr, K (C-Pr=1.5 mol%; C-kappa=1.5 mot%) crystals were studied at 294 and 80 K. Under optical excitation of the samples in the Pr3+ absorption bands, there were observed five fast ultraviolet emissions assigned to the 4f(1)5d -> 4f(2) transitions, and two long-wave bands corresponding to the f-f transitions. Furthermore, the intrinsic emission bands of SrCl2 were observed at 10 K. The X-ray excited luminescence spectrum of the SrCl2:Pr crystal containing 0.2 mol% Pr, besides intrinsic emission band near 400 nm, has got a long-wave band at about 490 nm of the Pr3+ centers. There were not observed any emission bands of the Pr3+ centers corresponding to the 4f(1)5d-4f(2) transitions in the X-ray excited luminescence spectrum of the SrCl2:Pr crystal. The possible mechanisms of energy transfer from the SrCl2 matrix to the Pr3+ centers are discussed.
Journal of Luminescence 01/2014; 145:13-18. DOI:10.1016/j.jlumin.2013.07.033 · 2.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Highlights
The energy band parameters of crystals have been calculated.
The effective mass of the electron at Г point has been estimated.
The average thermalization length of the electrons in CaF2, SrF2 and BaF2 crystals has been determined.
Book of abstracts of the 17 th International Conference on Luminescence and Optical Spectroscopy of Condensed Matter (ICL2014). 13-18 July, 2014. Wroclaw, Poland; 01/2014
[Show abstract][Hide abstract] ABSTRACT: The influence of the BaF2 nanoparticle size on the intensity of the self-trapped exciton luminescence and the radiative core-valence transitions is studied by the luminescence spectroscopy methods using synchrotron radiation. The decrease of the self-trapped exciton emission intensity at energies of exciting photons in the range of optical exciton creation (hν ≤ Eg) is less sensitive to the reduction of the nanoparticle sizes than in the case of band-to-band excitation, where excitons are formed by the recombination way. The intensity of the core-valence luminescence shows considerably weaker dependence on the nanoparticle sizes in comparison with the intensity of self-trapped exciton luminescence. The revealed regularities are explained by considering the relationship between nanoparticle size and photoelectron or photohole thermalization length as well as the size of electronic excitations.
[Show abstract][Hide abstract] ABSTRACT: The luminescent properties of Eu2+ ions in Ca3Sc2Si3O12 have been studied for the first time. The Eu2+-doped Ca3Sc2Si3O12 exhibit a broadband emission in the 720-1100 nm region with a maximum at about 840 nm, which is due to the 4f(6)5d -> 4f(7) transition of Eu2+ ions. This interpretation is supported by the appearance of the fine structure in the emission spectrum of Eu2+-doped Ca3Sc2Si3O12 at 77 K. Probably, the near infrared emission of Eu2+ ions in Ca3Sc2Si3O12 is the most long-wavelength 4f(6)5d -> 4f(7) emission of these ions within more than three hundreds of Eu2+-doped inorganic compounds studied to date.
Chemical Physics Letters 10/2013; 585:11-14. DOI:10.1016/j.cplett.2013.08.100 · 1.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Eu2+-doped Li2CaGeO4 samples have been prepared by the solid state reaction method and by thermolysis of the complex precursor. It was shown that Eu2+ ions in Li2CaGeO4 exhibit an intense emission with a maximum at 473 nm. The Stokes shift (820 cm−1) and full-width at half-maximum (1415 cm−1) of the emission band are close to those of the Eu2+ emission in Li2CaSiO4. Values of the crystal field splitting and the centroid shift of the Ce3+ 5d configuration in Li2CaGeO4 were also determined and compared with those of Ce3+ ions in Li2CaSiO4. Although the spectral positions of the Ce3+ lowest excitation band for Li2CaRO4 (R=Si, Ge) are practically the same, the magnitudes of the Ce3+ crystal field splitting appeared to be unexpectedly very different. This effect is tentatively attributed to a strong distortion of the calcium site in Li2CaSiO4 caused by the presence of the trivalent lanthanide ion.
Ceramics International 08/2013; 39(6):6835-6840. DOI:10.1016/j.ceramint.2013.02.015 · 2.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The study of the spectral-luminescence parameters of LaPO4-Eu and LaPO4-Pr nanoparticles upon excitation by the synchrotron radiation with photon energies 4–40 eV was performed. The differences of the luminescence intensity dependence on the size for LaPO4-Eu and LaPO4-Pr nanoparticles excited at the range of matrix transparency, the range of band-to-band transitions, and the range of electronic excitation multiplication were revealed. The observed regularities are explained in terms of the electron-phonon and electron-electron scattering, surface losses, and exciton diffusion. The ratio between the length of thermalization and electron mean free path and the size of nanoparticle is determinative for the luminescence intensity upon excitation in the range of fundamental absorption of matrix and X-ray excitation.
[Show abstract][Hide abstract] ABSTRACT: Polycrystalline samples of (Tb0.8Y0.2)3 (1-x)Ce3xAl5O12 (x = 0—0.03) are prepared by solid state reaction of Al2O3 and mixed rare earth oxides (Tb,Y)4O7:Ce (about 1300 °C, 3—5 h).
[Show abstract][Hide abstract] ABSTRACT: BaCl2:Eu2+ microcrystals embedded in the NaCl host have been obtained in the NaCl–BaCl2(1 mol%)–EuCl3(0.02 mol%) crystalline system. The influence of the annealing conditions on the formation of such particles has been studied. In particular, long-term annealing (at 200 °С during 100 h) promotes the microcrystals formation in the NaCl–BaCl2–Eu crystalline system. The subsequent heat treatment (annealed at 600 °С during 72 h and quenched to room temperature) is shown to lead to the destruction of the majority of these particles. The luminescent-kinetic properties of BaCl2:Eu2+ microcrystals have been studied upon the ultra-violet excitation by the synchrotron radiation. The X-ray excited luminescence has been measured in order to estimate the distribution of europium ions between microcrystals and the NaCl host. The excitation mechanisms of Eu2+ ions in the NaCl–BaCl2–Eu crystalline system are discussed.
Journal of Luminescence 03/2013; 135:1–4. DOI:10.1016/j.jlumin.2012.10.008 · 2.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Terbium-yttrium aluminum garnets (TYAG) doped with Ce3+ ions have been prepared by solid state reactions between nanostructured oxides of aluminum and rare earths. The luminescent properties of Ce3+ ions in (Тb0.8Y0.2)3(1−x)Ce3xAl5O12 (х = 0.03) have been studied upon excitation in the 2-20 eV region. The substitution of Tb3+ for Y3+ in the garnet structure results in broadening the emission band and shifting its maximum towards the longer wavelengths. It was found that in addition to the 4fn → 4fn−15d excitation bands of Ce3+ and Tb3+ ions, the excitation spectra for the Ce3+ emission contain broad bands at 6.73 and ∼9.5 eV. These bands are attributed to the Ce3+-bound exciton formation and O 2p → Al 3s, 3p transitions, respectively. In contrast to the predictions based on the results of electronic structure calculations on Y3Al5O12 and Tb4Al2O9, the threshold of interband transitions in TYAG is at high energies (⩾7.3 eV), and contributions from Altetr and Aloct atoms to the conduction-band density of states are evaluated as quite essential.
Journal of Alloys and Compounds 02/2013; 550:159-163. DOI:10.1016/j.jallcom.2012.09.053 · 3.00 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The luminescence properties of CaF2 nanoparticles with various sizes (20–140 nm) are studied upon the excitation by VUV and x-ray quanta in order to reveal the influence of ratio of mean free path and thermalization length of charge carriers and nanoparticle size on the self-trapped exciton luminescence. The luminescence intensity for exciting quantum energies corresponding to optical creation of exciton and to the range of electronic excitation multiplication is not so sensitive to nanoparticle size as for quanta with energy of Eg < hν < 2Eg. The dependences of luminescence intensity on nanoparticle size at the excitation by quanta of various energies are discussed in terms of electron-phonon and electron-electron scattering lengths and energy losses on surface defects.
[Show abstract][Hide abstract] ABSTRACT: We have studied the luminescent properties of Eu2+ and Eu3+ in the calcium chloride borate Ca2BO3Cl under optical and synchrotron excitation. The results demonstrate that a reductant should be present during synthesis in order to stabilize Eu2+ in Ca2BO3Cl and provide insight into the factors responsible for the long-wavelength position of the luminescence band (λmax = 577 nm) and the relatively low Eu2+ stability in Ca2BO3Cl.
[Show abstract][Hide abstract] ABSTRACT: LaCl 3 :Eu 2+ microcrystals dispersed in the NaCl matrix have been obtained in the NaCl–LaCl 3 (1 mol.%)– EuCl 3 (0.1 mol.%) crystalline system. The low-temperature luminescent properties of these microcrystals have been studied upon the VUV and UV excitation by the synchrotron radiation. The spectroscopic parameters as well as decay time constants of Eu 2+ -doped LaCl 3 host have been established. The excita-tion mechanism of divalent europium centers through energy transfer and reabsorption is discussed.
Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 03/2012; 275:78-82. DOI:10.1016/j.nimb.2011.11.024 · 1.12 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The luminescent properties of Eu2+ and Ce3+ ions in Li2SrSiO4 have been studied upon excitation in the 2–20 eV region. Based on the results of luminescent measurements, values of the crystal field splitting and the centroid shift of the Ce3+5d configuration in Li2SrSiO4 were found and compared with those of Ce3+ ions in some other inorganic compounds. The Eu2+ ions in Li2SrSiO4 exhibit a broad band emission with a maximum at 576 nm, which is due to the 4f65d→4f7 transition. It was shown that the long-wavelength position of the Eu2+ emission in Li2SrSiO4 is caused by the large crystal-field splitting of the Eu2+ 4f65d configuration and relatively high degree of covalency of the Eu–O bond. The stabilization of Eu2+ ions in Li2SrSiO4 during the synthesis process requires a strong reducing agent. Two phenomenological approaches to explain the low stability of Eu2+ in Li2SrSiO4 are also discussed.
Journal of Luminescence 02/2011; 131(2):310-315. DOI:10.1016/j.jlumin.2010.10.021 · 2.72 Impact Factor