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1.
The energy-transfer mechanisms and frequency upconversion emissions in 0.5Er 3+/ xHo 3+ co-doped tellurite glasses by exciting at 980 nm have been investigated. Three intense upconversion luminescence emissions are observed at around 525, 548, and 660 nm, which correspond to Er 3+: 2H 11/2 → 4I 15/2, Er 3+: 4S 3/2 → 4I 15/2 + Ho 3+: 5S 2( 5F 4) → 5I 8, and Er 3+: 4F 9/2 → 4I 15/2 + Ho 3+: 5F 5 → 5I 8 transitions, respectively. The upconversion emissions reach the maximum values when Ho 2O 3 is 0.5 mol%, and the intensities of the green and red light emissions were about 4.5 and 6 times stronger than those un-doped Ho 2O 3, respectively. The possible upconversion mechanisms and energy transfer between Er 3+ and Ho 3+ were also estimated and evaluated. All the three emissions are based on two photon absorption processes. 相似文献
2.
An analysis of the red to ultraviolet wavelength upconversion in Ho 3+ in SrLaGa 3O 7 and SrLaGaO 4 crystals is given. Upconverted, ultraviolet emission from the 3D 3 level under cw 647 nm excitation at room temperature was observed. Excitation of the 5F 5 level, corresponding to the 5I 8→ 5F 5 transition, leads to intense emission from the 5I 7, 5I 6, 5F 5, 5S 2, 5F 3, 3G 5 and 3D 3 levels. Based on the energy level diagram of Ho 3+, the pump intensity dependencies and experimental time dependencies of the observed emissions, an excitation scheme is proposed. 相似文献
3.
The spectroscopic behaviour of the Nd 3+ and Yb 3+ doped alkaline metal yttrium double phosphates, M 3Y 1−xLn x(PO 4) 2 (M=Na, Rb; x=0.01–0.3) were studied for both powder and single crystal samples. The high resolution absorption and emission spectra were measured in the visible and IR regions. Spectral changes with the Nd 3+ and Yb 3+ concentration were interpreted. The absorption strengths of the 4f–4f transitions were analysed and used to assess the structural modifications of the two double phosphates. Based on the 4 K absorption spectra the number of metal sites occupied by the dopants was investigated. Strong emission from Na3Y1−xNdx(PO4)2 involving the 4F3/2→4I9/2,4I11/2,4I13/2,4I15/2 transitions were observed whereas the corresponding emission from the rubidium phosphate was presumably quenched by multiphonon processes due to the water molecules absorbed in the channel-like structure. The IR spectra were used to assign the vibronic components of the electronic transitions. The Yb3+ emission bands were broadened depending on the Yb3+ concentration (1–10 mol%). The tentative energy level scheme of the ground and excited 2FJ (J=7/2, 5/2) levels was described. 相似文献
4.
Absorption and emission spectral properties of GdVO 4 single crystal doped with Ho 3+ ions were investigated at room temperature. Polarized absorption cross section is calculated in the range of 400–2200 nm. Results were analyzed and parameters were calculated based on Judd-Ofelt theory, the emission spectrum shows that the emission intensity around the wavelength of 546 nm associated with transition 5S 2 → 5I 8 is much stronger than other bands in the observed range and potentially enable the green light output around this emission band in this crystal. 相似文献
5.
We report the luminescence and upconversion spectra of nanocrystalline YAlO 3 doped with trivalent erbium at concentrations of 5.0, 1.0 and 0.1 mol.%. The powder samples were prepared using a solution combustion reaction method, and the resulting YAlO 3 nanocrystals show, under wide-angle X-ray diffraction, a size in the range 20–40 nm. Efficient green and red emissions are observed at room temperature under continuous-wave pumping at 980 nm. A weak emission can also be detected in the blue at 410 nm. The upconversion dynamics were studied measuring the decay times and the pump-power dependence of the transitions to the 4I 15/2 ground state starting from the 2H 11/2, 4S 3/2 and 4F 9/2 excited states. Excited-state absorption (ESA) is found to be responsible for the higher energy ( 2H 11/2, 4S 3/2→ 4I 15/2) green transitions. On the other hand, for the 4F 9/2→ 4I 15/2 red transition a competing energy-transfer upconversion (ETU) mechanism is found, which accounts for the more than 100-fold increase in intensity of the red emission on passing from the lowest (0.1 mol.%) to the highest (5 mol.%) erbium concentration. 相似文献
6.
The new phases KFe 2(SeO 2OH)(SeO 3) 3 and SrCo 2(SeO 2OH) 2(SeO 3) 2 have been synthesized under low-hydrothermal conditions and their structures were determined by single-crystal X-ray methods. Both compounds are monoclinic; KFe 2(SeO 2OH)(SeO 3) 3: space group P2, A = 9.983(4), B = 5.270(1), C = 10.614(4) Å, β = 97.42(2)°, V = 553.7 Å 3, Z = 2; SrCo 2(SeO 2OH) 2(SeO 3) 2: space group P2 ln, A = 14.984(2), B = 5.286(1), C = 13.790(2) Å, β = 94.72(1)°, V = 1088.5 Å 3 , Z = 4. The refinements converged to R-values of 2.9 and 3.6% respectively. The atomic arrangement in KFe2(SeO2OH)(SeO3)3 and SrCo2(SeO2OH)2(SeO3)2 is based on isolated MO6 octahedra (M = Fe3+, Co2+), which are corner-linked via trigonal pyramidal selenite groups to a framework structure. Interstitials are occupied by potassium or strontium atoms in ten- or eight-coordination respectively, and by the lone-pair electrons of the Se4+ atoms. Both compounds are not isotypic but are closely related and may be interpreted as different distortions of an idealized structure type in space group P2/m, which was modelled for a theoretical compound SrFe2(SeO3)4 by distance least squares refinement (program
). 相似文献
7.
Up-conversion luminescence has been studied in the Er 3+-doped oxyfluoride glass, its daughter nano-glass–ceramics and the polycrystalline ErF 3 when excited at infrared wavelengths of either 800 or 980 nm. The mechanism of the up-conversion luminescence is shown to differ for excitations at 800 and 980 nm since the different excited levels of the Er 3+ are involved, respectively. An order of magnitude increase of red-to-green up-conversion luminescence ratio has been observed with nano-ceramming of the precursor glass when excited at 800 nm and a full dominance of the red up-conversion luminescence has been observed in the ErF 3 at the both excitation wavelengths. Observed changes in the spectra of the up-conversion luminescence from the precursor glass to its daughter nano-glass–ceramics provide a tool for tuning the colour of the up-conversion luminescence by ceramming of the precursor glass. These changes are shown to be due to decrease of the vibration energy of phonons coupled to the Er 3+ ions embedded to the PbF 2 nano-crystals with nano-ceramming. Hence we report for the first time that the red up-conversion luminescence from the Er 3+-doped material can be due to the radiative transition 4F 5/2, 4F 3/2 → 4I 13/2 of the Er 3+ ion, which is principally allowed only in such a low-phonon energy host as the PbF 2 nano-crystals, while such red up-conversion luminescence is almost completely non-radiatively quenched in the oxyfluoride precursor glass. The up-conversion emission spectrum of the ErF 3 is dominated by a cross-relaxation mechanism typical of hosts with a very high doping level of the Er 3+ ions. 相似文献
8.
We report the results of structural studies by means of Eu 3+ fluorescence line narrowing techniques in the binary systems PbF 2-GeO 2 and PbF 2-SiO 2. Several features characteristic of the europium fluorescence in lead glasses are put forward. The absence of selectively excited emission at room temperature demonstrates an unusually large homogeneous broadening of the electronic levels. A relative increase in the 5D 0 → 7F 1 (magnetic dipole) with respect to the 6D 0 → 7F 2 (electric dipole) transition is observed with time-resolved. detection. This effect shows that accidental coincidences of 5D 0 → 7F 0 energies and 7F 1 splitting do occur between europium sites differing only by their 6D 0 lifetimes and magnetic dipole: electric dipolar relative intensities. The general characteristics are interpreted with oxygen neighbours for Eu 3+ rather than fluorine ions. The crystal field strength expressed as Nv = [∑ k,a ( Bgk) 2 × 4π/(2 k + 1)] 1/2 (limited to k=2 parameters) is slightly higher in the germanate than in the silicate matrix. 相似文献
9.
The example of three trivalent neodymium compounds Na 3Nd(ODA) 3·2NaClO 4·6H 2O, Nd 2Mg 3(NO 3) 12·24H 2O and LiYF 4/Nd 3+ is used to show how the simulation of the magnetic circular dichroism transitions in addition to the simulation of the -spectrum can provide an independent tool for checking the reliability of the wave functions and intensity parameters. The 4F 9/2← 4I 9/2 transition, which is clearly observed in all three samples, is used here to illustrate the simulation procedure. 相似文献
10.
Absorption spectra have been studied in 190–3100 nm region at various temperatures from 16 to 292 K for Yb 3+-doped and Yb 3+/Nd 3+-, Yb 3+/Er 3+- and Yb 3+/Pr 3+-co-doped LiNbO 3 single crystals before and after γ-irradiation with a dose of 10 5–10 7 Gy. Intense 400 and 500 nm absorption bands were observed after γ-irradiation, which are due to the creation of oxygen vacancy (F-type color center) and Nb 4+ polaron, respectively. Different change was observed in the 2870 nm OH − absorption band intensity among the various rare-earth doped crystals. These are interpreted by discrepancy of ionic radii between substituting rare earth dopant ion and Li + or Nb 5+ host ion. The observed temperature dependence of the hot bands is understood by electronic transition from the thermally populated 2F 7/2 Stark levels to the excited 2F 5/2 level. The position of the Yb 3+ 2F 7/2→ 2F 5/2 first resonant line was observed to be slightly different among the co-doped crystals. This is due to the perturbation of Yb 3+ by co-doped rare earth ion which is located at the neighborhood of theYb 3+. 相似文献
11.
In the present work, the spectroscopic and magnetic properties of heteronuclear Cu:Pr squarate are reported. Single crystals of [Pr 2Cu(C 4O 4) 4(H 2O) 16]·2H 2O were obtained by reaction of squaric acid, praseodymium chloride and copper chloride in water solution according to the procedure described earlier. The crystals of title compound are isomorphic with [La 2Cu(C 4O 4) 4(H 2O) 16]·2H 2O crystal, where squarate anions participate as bridging ligands between metal ions. The UV region of absorption spectra of the title compound is dominated by C–T band of Cu(II), f–d transition of Pr(III) and internal π–π*(A1g→Eu) and π–π*(A1g→Eg) ligand transitions. In visible and IR regions, t2g–eg of copper Cu(II) as well as 3H4→3PJ, 1D2, 1G4, 3FJ, 3H6 Pr(III) transitions at 293 and 4 K were recorded. At low temperature splitting given by Jahn–Teller effect can be observed. Significant anisotropy of d–d transitions intensities confirms well the Jahn–Teller effect, too. Unexpectedly high intensity of 3H4→1G4 transition is probably due to the intensity borrowing from the Cu (II) d–d transition. The 3P0 and 1D2 emission of Pr(III) in the [Pr2Cu(C4O4)4(H2O)16]·2H2O crystals is quenched even at 77 K. Whereas emission of appropriate polynuclear europium squarate was detected. The pathways of excited state quenching by eg levels of Cu(II), multhiphonon relaxation and concentration quenching can be considered in the system under studies. Magnetic susceptibility measurements were carried out in 300–1.7 K temperature range and are discussed in relation to the structure. Effect of the polymeric structure on spectroscopic behaviour is presented. Selectivity of polymeric europium squarate in vitro test for different tumor cells is shown. 相似文献
12.
Praseodymium dicarboxylate, [Pr(H 2O)] 2[O 2C(CH 2) 3CO 2] 3.4H 2O]–glutarate, Pr[glut], is synthesized by hydrothermal techniques. The title compound crystallizes in the monoclinic space group C2/c (No. 15). The rare earth cation is coordinated by nine oxygen atoms, eight oxygen atoms from the carboxylate groups and one from the water molecule. The local symmetry of Pr site is low, C s. The absorption spectra of Pr[glut] are recorded from the visible to the far IR domain at 300, 77 and 9 K. Under various Ar + laser excitations no emission is detected from 3P 0 and 1D 2 excited levels of Pr 3+ ion. In the low temperature absorption spectra only one electronic line is recorded for 3H 4→ 3P 0 transition. It confirms a unique local environment for the rare earth ion in Pr[glut]. The utility of the ‘barycenter curves’ in the attribution of electronic lines is demonstrated. Energy level scheme of 36 Stark components is deduced from the absorption spectra. The parametric calculation was performed on the whole 4f 2 (Pr 3+) configuration with the starting set of crystal field parameters obtained previously for the Eu 3+ ion in the isostructural compound. Eight free ion and nine phenomenological crystal field parameters in C 2v symmetry reproduce quite well several electronic levels of Pr 3+ ion experimentally observed in Pr[glut]. A good r.m.s. standard deviation of 14.8 cm −1 is obtained. 相似文献
13.
The results of the high-resolution absorption, selective excitation, time-resolved emission and emission kinetics of Eu 3+ in GdCOB and EuCOB single crystals are presented. The Eu 3+ spectra show at least three non-equivalent centers whose static spectral characteristics were used to assign structural models. The crystal field parameters were estimated for prevailing Eu 3+ center in EuCOB. The inhomogeneous broadening and shifts of the 5D 0→ 7F 0 and 5D 0→ 7F 1 Eu 3+ lines in GdCOB under selective excitation in main lines were explained by J mixing of 7F 2 states into 7F 1 and 7F 0 by second order crystal field terms and connected to disordered structure in cationic spheres. 相似文献
14.
The absorption, magnetic circular dichroism and luminescence spectra of monomeric pseudo trigonal planar (η 5-Me 3SiC 5H 4) 3Pr III (Cp′Pr) have been measured at room and at low temperatures. Applying the selection rules for molecular D 3h symmetry, a truncated crystal field (CF) splitting pattern (which comprises essentially excited Γ 4 and Γ 6 states) could be derived. The parameters of an empirical Hamiltonian were fitted to the energies of 24 levels to give an r.m.s. deviation of 21.4 cm −1. On the basis of the CF parameters obtained, the CF strength of one Cp ligand was estimated. 相似文献
15.
The binary phosphate K 4Ce 2P 4O 15 was prepared in the polycrystalline state in the solid state reaction of cerium oxide and potassium phosphate KPO 3. The phosphate fragment of this compound appears in the form of two PO 43− and one P 2O 74− anions occupying the sites of low symmetry. Electronic absorption, emission as well as infrared and Raman spectroscopic methods have been applied to characterise the properties and structure of the compound studied. Its electronic spectra agree with the Ce 3+ ion spectroscopic characteristics. The 2F 5/2→ 2F 7/2 transition appears in the typical for this ion region: about 2000 cm −1. The multiplet structure of the spectrum suggests the existence of at least two crystallographic different sites of this ion in the unit cell. The absorption bands in the range 25000–45000 cm −1 have been assigned to the 4f 1→5d 1 transitions of the cerium ion and CT transition of the phosphate ligands. The vibrational spectra were discussed on the basis of correlation diagrams and factor group analysis. The radiation-less mechanism of the return from the excited state to the ground state via CT states in the system studied is proposed. 相似文献
16.
A single-crystal X-ray structural investigation of [Tb(C 5H 5) 2Br] 2 revealed the [Sc(C 5H 5) 2Cl] 2-type structure, space group P2 1/ c, with a = 1407.6(2) pm, b = 1644.7(2) pm, c = 1370.6(9) pm, β = 93.46(3)°, V = 3167(2) × 10 6 pm 3, Dc = 2.322 g cm −3 and Z = 6 dimers ( R = 0.036 for 4627 reflections with I > 3σ( I)). The metal centres have the pseudosymmetry C2v. Magnetic susceptibility data show Curie-Weiss behaviour between 213 and 6 K with θ p = −4.5(3) K and a magnetic moment μ = 9.8(1) μ B close to the Tb 3+ free-ion value (9.72 μ B). Below 6 K, deviations from Curie-Weiss behaviour are observed, and at 5.3 K a maximum in the susceptibility is detected which may be caused by intradimer antiferromagnetic spin coupling. The magnetic properties are compared with the prediction of various models, starting from cubic crystal fields and isotropic intramolecular exchange interactions, followed by extension to lower crystal field symmetry (orthorhombic) and anisotropic contributions to the spin coupling. However, a reasonable agreement between the measured and calculated data was not obtained. As in [Gd(C 5H 5) 2Br] 2, the low-temperature behaviour is governed by effects which cannot be described by spin coupling models in the generally accepted form. 相似文献
17.
Single crystals of a new ternary nitride, Ba 5Si 2N 6, were synthesized by slow cooling from 750°C using a starting mixture of Ba, Si, Na and NaN 3, where Na and NaN 3 were a flux and a nitrogen source respectively. It crystallizes with orthorhombic symmetry: space group P2 12 12 1 (No. 19), A = 6.159, B = 10.305, C = 15.292 Å, and Z = 4. The crystal structure was determined from single-crystal data and refined to R1 = 0.0495 for all 1637 observed reflections and 89 variables. A pair of SiN 4 tetrahedra contained in the structure forms a nitridometallate anion of [Si 2N 6] 10 by edge sharing. 相似文献
18.
The formation of cation solid solution in the (La 1−xGd x)OCl:Eu 3+ (0≤ xGd≤1; ΔxGd=0.1) series was studied by photoluminescence spectroscopy. The luminescence from the 5D 0–2 to the 7F 0–4 levels of the Eu 3+ ion in the (La 1−xGd x)OCl series was recorded at 77 K by using argon ion laser excitation (457.9 nm). The interpretation of the spectra according to the C 4v site symmetry of the Eu 3+ ion in the tetragonal PbFCl-type structure yielded nearly complete sets (18 to 19 levels) for the 7F 0–4 levels. Simulations of the Stark level schemes were carried out with the aid of a phenomenological c.f. theory utilizing the five non-zero c.f. Bqk parameters ( B02, B04, B44, B06 and B46) allowed for the C 4v site symmetry. By using the calculated c.f. parameter sets a quantitative measure was obtained to monitor the formation of cation solid solutions. The strength of the c.f. effect was estimated with the c.f. strength parameters S and Sk ( k=2, 4 and 6). The c.f. parameter sets reproduced the experimental 7F J ( J=0–4) energy level schemes with the rms deviations between 4 and 11 cm −1. The individual parameters as well as the c.f. strength parameters were found to evolve in a smooth manner indicating complete solid solubility in the (La 1−xGd x)OCl series. Some local distortions from the C 4v symmetry — probably of long range—leading to the splitting of the 7F 1 doubly degenerate E level were observed, however. 相似文献
19.
Europium doped phosphors Ca 3La 3(BO 3) 5 were first synthesized by a sol–gel process technique. The reaction temperature of the sol–gel process was 300 °C lower than that of the solid-state reaction and the reaction time of the sol–gel process was shorter. The photoluminescence properties of Eu 3+ doped Ca 3La 3(BO 3) 5 indicated that the phosphors exhibited a strong luminescence of 5D 0– 7F 2 transition at 612 nm under the excitation at 237 nm. The emission intensity of the phosphors prepared by the sol–gel process was higher than those prepared by the solid-state reaction. The relationship between optical properties and morphologies were studied. In particular, Li + ion doping effectively enhanced the luminescent properties of the Eu 3+ doped Ca 3La 3(BO 3) 5 phosphors. The highest brightness was observed in the phosphor Ca 3La 2.82Eu 0.1Li 0.08B 5O 15−δ prepared by the sol–gel process. 相似文献
20.
Absorption, emission, and luminescence excitation spectra of the LiNbO 3 crystal doped with 0.5% Pr 3+ and 0.8% Yb 3+ are presented. Additionally the photoluminescence spectra at high pressure have been measured. Hydrostatic pressures up to 135 kbar were applied with a diamond anvil cell. Absorption of the Pr 3+:LiNbO 3 crystal is characterized by the strong threshold at about 400 nm, related to the band-to band-transitions and the sharp structure in the visible region attributed to the transitions to 3P J and 1D 2 levels of Pr 3+ ion. After the 488 nm excitation the yellow emission related to the 1D 2→ 3H J transition of Pr 3+ have been observed when the 3P 0 emission has not been detected. The excitation spectra of the 1D 2 luminescence consist of the sharp lines related to the 3H 4→ 3P J ( J=0, 1, 2) transitions and two broad bands peaked at 340 and 400 nm related probably to the bound exciton. The 1D 2→ 3H J emission shifts with pressure toward the lower energies with the rate of −2.4 cm −1 kbar −1. Additionally, for higher pressures the 1D 2 emission is considerably quenched. This is explained as being due to the decrease of the energy of the bound exciton with pressure which results in the higher nonradiative depopulation rate of the 1D 2 state. 相似文献
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