Forced Electric Dipole Transition Research Articles

Mechanoluminescence and photoluminescence properties of Eu3+ -activated SrGa2 O4 phosphors.

Red-emitting Eu3+ activated SrGa2 O4 phosphors were synthesized using a conventional solid-state reaction method. The structural, optical, and luminescence properties were systematically investigated. The synthesized phosphors are single phase with a monoclinic structure. There are no significant changes in the phase and the crystal structure of the host matrix after incorporating Eu3+ ions. The undoped and Eu3+ doped SrGa2 O4 phosphors exhibited good mechanoluminescence (ML) emission without any irradiation with ultraviolet (UV) or gamma rays. Eu3+ -activated SrGa2 O4 phosphors have prominent red emission attributed to 5 D0 → 7 F2 forced electric dipole transition excited at 395 nm. The colour coordinates and purity of the SrGa2 O4 : 0.08 Eu3+ phosphor were calculated to be (0.6102, 0.3810) and 97.6%, respectively. The quantum efficiency is 12.68%, and was better than that of commercially available red phosphors. The ML and photoluminescence studies revealed that the synthesized phosphors can act as potential candidates for stress sensors, UV or near-UV light-emitting diodes (NUV LEDs) and components of phosphor-converted white light-emitting diode (pc-WLED) applications.

Improvement in white light emission of Dy3+ doped CaMoO4 via Zn2+ co-doping

The research in developing a single ingredient phosphor for white-light emission is progressively increasing. It is well known that the 4F9/2 → 6H13/2 (yellow) and 4F9/2 → 6H15/2 (blue) transitions of Dy3+ ions give near-white light emission. The white light emission of Dy3+ ions can be enhanced via improving the crystallinity of the host phosphor via co-doping of transition metal ions. In this paper, we report a significant improvement in the white light emission of Dy3+ doped CaMoO4 by co-doping Zn2+ ions. The x-ray diffraction pattern confirms the tetragonal phase of pure and doped CaMoO4 phosphor. The peak broadening and a red-shift in the absorption peak are observed by UV–vis absorption analysis of Zn2+/Dy3+ doped CaMoO4. From Photoluminescence studies, we have observed that in Dy3+ doped CaMoO4, the 4% Dy3+ doped CaMoO4 exhibits maximum emission. The Zn2+ ions are co-doped to further increase the luminescence intensity of CaMoO4:4%Dy3+ and the maximum luminescence is obtained for 0.25% Zn2+ concentration. Two intense emission peaks centered at 484 nm and 574 nm related to transitions 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 of Dy3+ ion are observed for Dy3+ doped phosphor. The 4F9/2 → 6H13/2 transition is the forced electric dipole transition which is affected by its chemical environment. After Zn2+ co-doping, the 4F9/2 → 6H13/2 transition is affected due to a change in asymmetricity around the Dy3+ ions. The 0.25% co-doping of Zn2+ gives 34% enhancement in luminescence emission of 4% Dy3+ doped CaMoO4. As a result, the CIE coordinates of chromaticity diagram and the color purity of the 0.25% Zn2+ co-doped CaMoO4:4Dy3+ show improvement in the overall white light emission. We have shown that with Zn2+ co-doping, the non-radiative relaxations are reduced which results in improved white light emission of Dy3+ions.

Excitation dependent site-specific luminescence and structure-optical property correlation of Lu2Sn2O7:Eu3+ nanoparticles

Abstract Understanding of structure-property correlation is of paramount importance in designing phosphors which impact the advanced lighting technology. Here, for the first time, we have synthesized La2Sn2O7:Eu3+ (LSOE) nanoparticles (NPs) and investigated their optical properties under host and Eu3+ intra-configurational f-f excitations at 274 and 395 nm, respectively. Under 274 nm excitation, Eu3+ ions are found to localize at both LaO8 and SnO6 polyhedra to an equal extent, which leads to comparable intensity of the forced electric dipole transition (FEDT) and magnetic dipole transition (MDT). Under 395 nm excitation, Eu3+ ions at SnO6 polyhedra is selectively excited, which gives more intense FEDT. Accordingly, the LSOE NPs give orange and red emissions under 274 nm and 395 nm excitations, respectively. The quenching concentration of Eu3+ ions in the LSOE NPs is 5.0 mol% due to multipolar interactions. Maximum asymmetric ratio happens for the LSOE NPs at the doping level of 7.5% due to the largest fraction of Eu3+ ions at SnO6 polyhedra. Reversely, longest lifetime occurs for the LSOE NPs at the doping level of 0.5% owing to enhancing defect density at elevated Eu3+ doping. Point group symmetry of Eu3+ ions is C3 based on Stark splitting determination. Judd-Ofelt analysis suggest that the excitation of the LSOE NPs at 395 nm leads to narrow red emission with lower non-radiative transition and higher internal quantum yield. Our work is expected to excite more luminescence scientists to explore the application potentials of the Lu2Sn2O7 NPs for color-tunable optoelectronics, solid state lighting and bioimaging.

Influence of Structural Disorder on the Photoluminescence Properties of Eu3+ Doped Red Phosphors: Ca2Y3‐xNb3O14: xEu3+

AbstractEu3+ doped pyrochlore type red phosphors, Ca2Y3‐xNb3O14 were prepared by a conventional solid state reaction route. The Eu3+ incorporation induces structural disorder in the lattice reducing the pyrochlore D3d symmetry as evidenced by the diminishing of characteristic superlattice peak (111) in the XRD pattern and the absence of 5D0 ‐7F1 MD transition splitting. Rietveld refinement and Raman analysis corroborate the presence of Eu3+ ion on the B site for lower concentrations attributing to the structural disorder. The variation of Eu3+ ion coordination is further confirmed by the shift in the position of charge transfer band to a lower energy for higher concentrations. The preferential occupation of Eu3+ ions on the B site conduces a higher coordination more than VI with disordered environment allowing forced electric dipole transitions. The abrupt change of 5D0 ‐7F0 and 5D0 ‐7F2 life times at higher concentrations (x=1.25) further confirms the decrease in symmetry of Eu3+ ions to the pyrochlore D3d symmetry. These phosphors emit intense red light due to forbidden electric dipole transition with more Stark splitting indicating the low symmetry of Eu3+ ions in the host. The Judd‐Ofelt intensity parameters ΩJ supports the site symmetry and luminescence behavior of Eu3+ ions in the host. The disordered environment with special coordination of Eu3+ ions allows improved quantum efficiency (η=34 %) and CIE color coordinates (0.61, 0.38).

Photoluminescence properties of ordered Bi4−xNdxTi3O12 matrix supported by 3-dimensional silicon microchannel plate

Ordered ferroelectric neodymium (Nd)-substituted bismuth titanate (Bi4−xNdxTi3O12) is fabricated on silicon microchannel plates (Si-MCPs). A significantly enhanced photoluminescence peak at about 890 nm (∼1.4 eV) corresponding to the 4 f3 − 4 f3 forced electric dipole transition from the 4I9/2 ground state to different excited states of Nd3+ is observed. Moreover, the near-infrared emission intensity can be tuned by adjusting the Nd composition. The effects can be ascribed to the difference in the host lattice between the Nd-doped titanate with a simple perovskite structure and the result rendered by the regular cubic array of the Si-MCPs.

Synthesis and white light emission of Dy 3+ ions doped hexagonal structure YAlO 3 nanocrystalline

A series of hexagonal YAlO 3 with various Dy 3+ ions concentrations were synthesized via a facile sol–gel combustion method. The samples were characterized by XRD, TEM, FT-IR and PL measurements. Results show that the Dy 3+-doped hexagonal YAlO 3 can commendably output white light, which consists of the blue 487 nm ( 4F 9/2→ 6H 15/2) and the yellow 578 nm ( 4F 9/2→ 6H 13/2) emissions. The high intensity of hypersensitive forced electric dipole transition ( 4F 9/2→ 6H 13/2) is due to the serious destruction of crystal field symmetry surrounding Dy 3+ ions.

Template-free synthesis, characterization, growth mechanism and photoluminescence property of Eu(OH) 3 and Eu 2O 3 nanospindles

A simple aqueous solution route was introduced for the fabrication of uniform Eu(OH) 3 and Eu 2O 3 nanospindles, nanorods and nanobundles by using Eu(NO 3) 3 and NaOH as the starting reaction reagents at room temperature and atmosphere pressure without any surfactant and template. The influence of the molar ratios of [OH −]/[Eu 3+], reaction time, and temperature was investigated. It is demonstrated that the size of Eu(OH) 3 nanospindle can be well tuned by adjusting the [Eu 3+]/[OH −] molar ratios. The possible growth mechanism of Eu(OH) 3 and Eu 2O 3 nanostructures is also discussed. The room-temperature photoluminescence analysis shows that Eu 2O 3 nanostructures have an intensive emission peak of Eu 3+ ion at around 611 nm due to the 5D 0– 7F 2 forced electric dipole transition of Eu 3+ ions. It is found that the relative peak intensity increases with increasing reaction time.

Facile synthesis, characterization, formation mechanism and photoluminescence property of Eu 2O 3 nanorods

A large-scale synthesis of uniform Eu 2O 3 nanorods was realized without templates by a simple precipitation method under ambient pressure with the subsequent calcination. The products were characterized by X-ray diffraction spectroscopy, transmission electron microscopy, scanning electron microscopy, thermogravimetry and differential scanning calorimetry. It is demonstrated that the Eu 2O 3 nanorods with the pure body-centered cubic structure have a diameter of ∼20 nm and a length of 100–300 nm. The influence of reaction temperature, solution concentration, and reaction time on the formation of nanorods is investigated, and the possible growth mechanism is also discussed. The room temperature photoluminescence analysis shows that Eu 2O 3 nanorods have a strong red emission peak of Eu 3+ ion at around 611 nm due to the 5D 0 → 7F 2 forced electric dipole transition of Eu 3+ ions.

Reflux synthesis, formation mechanism, and photoluminescence performance of monodisperse Y 2O 3:Eu 3+ nanospheres

Monodisperse Y 2O 3:Eu 3+ nanospheres have been successfully synthesized by a low-temperature reflux method assisted by cetyltrimethyl ammonium bromide (CTAB). The products were characterized by X-ray diffraction spectroscopy, transmission electron microscopy, scanning electron microscopy, Fourier-transform infrared spectrophotometer, thermogravimetric and differential thermal analysis, and X-ray photoelectron spectroscopy. It is demonstrated that the size of Y 2O 3:Eu 3+ nanospheres can be controlled from 80 to 140 nm with narrow size distribution by adjusting the amount of CTAB. A possible formation mechanism of Y 2O 3:Eu 3+ nanospheres has been proposed. The photoluminescence analysis shows that Y 2O 3:Eu 3+ nanospheres obtained have a strong red emission peak of Eu 3+ ions at around 611 nm, due to the 5D 0 → 7F 2 forced electric dipole transition of Eu 3+ ions. It is found that the photoluminescence performance of the obtained Y 2O 3:Eu 3+ nanospheres is stronger than that of the Y 2O 3:Eu 3+ nanorods synthesized by a traditional hydrothermal route.

Photoluminescence investigations of YAG:Eu nanocomposite powder by high-energy ball milling

Europium-doped nanosized yttrium aluminum garnet (YAG) powders and bulk YAG powders were synthesized by using a planetary ball mill and a conventional solid-state reaction method, respectively. The grain size effects of the crystallinity, morphology, structure, and luminescence spectra were investigated by using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and photoluminescence spectroscopy measurements. In the case of nanocrystalline YAG:Eu 3+ powder, the luminescence intensity is dominated by the magnetic dipole transition 5D 0 → 7F 1 (590 nm) than the 5D 0 → 7F 2 forced electric dipole transition (612 nm).

Synthesis and strong red photoluminescence of europium oxide nanotubes and nanowires using carbon nanotubes as templates

Europium oxide nanotubes and nanowires have been successfully synthesized by a facile solvothermal method using carbon nanotubes (CNTs) as removable templates. The products were characterized by X-ray diffraction spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectrometry, Fourier-transform infrared spectrophotometry, thermogravimetric and differential thermal analysis, and X-ray photoelectron spectroscopy. It is demonstrated that CNTs are fully coated with an amorphous Eu(OH) 3 layer, which is ∼12 nm thick and almost continuous and uniform. After the Eu(OH) 3/CNTs composites have been calcined at various temperatures, europium oxide nanotubes and nanowires are obtained by removing the CNT templates. The inner diameter of the europium oxide nanotubes is 40–60 nm, which is consistent with that of CNTs. Both nanotubes and nanowires have a narrow distribution of diameters. Furthermore, the photoluminescence properties of the europium oxide nanotubes and nanowires calcined at various temperatures have been systematically investigated. The results indicate that when the Eu(OH) 3/CNTs composites were calcined at 600 °C for 6 h, the europium oxide nanotubes obtained have a strong red emission peak of Eu 3+ ions at around 611 nm, due to the 5D 0 → 7F 2 forced electric dipole transition of Eu 3+ ions. It is very interesting to discover that a few residual carbons doped in europium oxide nanotubes and many oxygen vacancies could promote the intensity of red emission peak of Eu 3+ ions. In addition, europium oxide nanowires calcined at 1050 °C for 6 h also have a strong red emission peak due to many vacancies, such as oxygen vacancies, and defects formed on the surface of the nanowires and inside them.

Synthesis and photoluminescence of Eu3 + in Y1−xGdxAlO3 nanophosphors

Europium-doped Y1−xGdxAlO3 perovskite (YAP) nanophosphors were synthesized by a solvothermal method. A YAP phase without impurity was formed from phosphors sintered at 1100 ° C. All the phosphors except YAlO3 can be estimated as mixed cubic and orthorhombic YAP phase. With the increase in Gd, the crystallinity was changed from simple cubic to q mixed phase of cubic and orthorhombic. Due to a 5D0→7F2 forced electric dipole transition of Eu3+, the nanophosphors with two mixed phases emitted radiation of red light with a 614 nm wavelength, whose brightness was dramatically increased by a factor 8 in comparison to that of the cubic perovskite phase. It is ascribed to the enhancement of non-symmetric environment for the Eu3+ in the nanophosphors with two mixed phases. The intensity ratios (IED/MD) between the structural hypersensitive force electric dipole transition, 5D0→7F2, and the intensity of the magnetic dipole transition, 5D0→7F1, are 0.4 for cubic phase and 1.4 for mixed phase.

Radiative Properties of Transparent PLZT Doped with Tm3+ for Active Electro-optical Applications

The optical transition probability of Tm3+ (7.0 mol%) doped PLZT was investigated because of its great interest in many fields such as optical communications in the mid-infrared waveband and medical instrumentation. The absolute intensities of its forced electric dipole transitions between 420 and 2000 nm were measured. According to Judd-Ofelt (J-O) theory, three phenomenological parameters, 2=9.1331021 cm2, 4=1.5291021 cm2 and 6=1.7121021 cm2, were obtained. The J-O intensity parameters were used to calculate the radiative lifetime (7.493 ms) of the excited 3F4 level. The stimulated emission cross-section for the 3F43H6 transition was also evaluated. Analysis reveals that Tm3+-doped PLZT is promising for use as efficient optical amplification devices or zero-loss electro-optical devices.

Optical Transition Probability of Nd3+ Ions Doped inFerroelectric Plzt for Active Electro-Optical Applications

The optical transition probability of Nd3+ (0.5 mol%) dopedlanthanum-modified lead zirconate titanate (PLZT) is investigated. Theabsolute intensities of its forced electric dipole transitions between400 nm and 1000 nm were measured, from which we obtain threephenomenological parameters, Ω2 = 0.787×10−20 cm2,Ω4 = 1.182×10−20 cm2, and Ω6 = 1.042×10−20 cm2, according to the Judd–Ofelt theory. Theradiation lifetime (346.9 μs) of the 4F3/2 metastablestate, the stimulated emission cross-section σij (2.49×10−21 cm2, 6.51×10−21 cm2, 2.17×10−21 cm2) and the fluorescence branch ratios are calculated.We also measured the fluorescence lifetime (155.84 μs) andcalculated the quantum efficiency (46.1%). The analysis reveals thatNd3+-doped PLZT, based on its large electro-optical effect, haspotential applications in active optical devices.

Interference between Judd-Ofelt and Wybourne-Downer mechanisms in the5D0−7FJ(J=2,4) transitions ofSm2+in solids

The strengths of the $^{5}$${\mathit{D}}_{0}$${\mathrm{\ensuremath{-}}}^{7}$${\mathit{F}}_{\mathit{J}}$ (J=0,2,4) optical transitions of the ${\mathrm{Sm}}^{2+}$ ion in solids, which are due to the forced electric dipole transition, are analyzed by taking into account not only the Judd-Ofelt mechanism but also the excited-state spin-orbit interaction (Wybourne-Downer) mechanism. The fact that the $^{5}$${\mathit{D}}_{0}$${\mathrm{\ensuremath{-}}}^{7}$${\mathit{F}}_{0}$ transition strength of the ${\mathrm{Sm}}^{2+}$ ion is much larger than that of the isoelectronic ${\mathrm{Eu}}^{3+}$ ion in various crystalline and glassy matrices is ascribed to the resonance effect which results from the presence of the 4${\mathit{f}}^{5}$5d states of ${\mathrm{Sm}}^{2+}$ in the vicinity of the 4${\mathit{f}}^{6}$ states concerned with the optical transition. However, such an enhancement of the transition strength due to the energetic resonance between the 4${\mathit{f}}^{6}$ and 4${\mathit{f}}^{5}$5d states is not observed in the $^{5}$${\mathit{D}}_{0}$${\mathrm{\ensuremath{-}}}^{7}$${\mathit{F}}_{2,4}$ transitions of ${\mathrm{Sm}}^{2+}$ in solids. This is identified as due to the interference between the Judd-Ofelt and Wybourne-Downer mechanisms. \textcopyright{} 1996 The American Physical Society.

Vibronic transitions of rare earth ions

An overview of recent research on vibronic transitions of intraconfigurational 4f n transitions in rare earth ions is given. The strong variation in vibronic coupling strengths is shown to depend on the type of rare earth ion and the chemical nature of the ligands. In the discussion of the mechanism of vibronic coupling, new evidence for the importance of Δ process vibronics (or Franck-Condon phonon replicas) next to the usually considered M process vibronics (or vibrationally induced forced electric dipole transitions) is presented. Concentration enhancement of vibronic transitions in the excitation spectra of Pr 3+ in several covalent host lattices is reported. A model based on superexchange interaction between Pr 3+ ions over distances of about 11 Å can account for the observed concentration enhancement.

Enhancement of the second-order Judd-Ofelt transition rates for high-lying (4f) states

The Judd-Ofelt approximation to the forced electric dipole transition strengths has been used with considerable success to model the sharp intra-configurational (4f)n-(4f)n spectra of rare earth ions in solids. However, discrepancies are observed when the model is applied to the highest lying (4f)n states. We describe here a modification of the standard second order Judd-Ofelt theory which allows us to calculate the enhanced transition rates in cases where one state is close to the perturbing band. When mixing with one configuration dominates, our theory requires no new adjustable parameters; both the enhanced even parameters and a new set of odd parameters can be calculated from the three even Judd-Ofelt parameters determined by fitting the transition rates between the low-lying states. Our theory is able to account for the transition rates we observe from the (4f)2 1S0 state of Pr3+ : LaF3 (just below the 4f5d band), without resort to third or fourth order configurational interaction terms.

Terbium luminescence-lifetime heterogeneity and protein equilibrium conformational dynamics.

The fluorescence decay of the rare earth terbium when bound to the protein calmodulin changes from a simple exponential decay to a complex nonexponential decay as the temperature is lowered below 200 K. We have fit the observed decay curves by assuming that the terbium emission is a forced electric dipole transition and proteins have a distribution of continuous conformational states. Quantitative fits to the data indicate that the root-mean-square configurational deviation of the atoms surrounding the terbium ion is 0.2 A, in good agreement with other measurements. We further point out that because the protein seems to undergo a glass transition yet retains configurational order at room temperature, the proper name for the physical state of a protein at room temperature is the rubber-like state.

Absorption spectra of dysprosium compounds in nonaqueous solutions. Spectral intensity analysis

Absorption spectra of dysprosium compounds were measured in amides and D 2O within the 5500–35000 cm −1 region and in alcohols within the 7000–34300 cm −1 region. The oscillator strengths of f-f absorptions bands below 35000 cm −1 were determined. The intensities of the Dy 3+ ground state absorption were analyzed according to the Judd-Ofelt theory of forced electric dipole transitions. A good fit to the measurements was obtained with the intensity parameter given in Tables 4–6. The polarizability effect on the intensity of the f-f transition with high value matrix elements U (4) and U (6) were considered.

ChemInform Abstract: THE TERBIUM CHLORIDE‐ALUMINUM CHLORIDE VAPOR SYSTEM. III. SPECTRAL INTENSITY ANALYSIS

The intensities of Tb3+ ground state absorption and 5D4 fluorescence transitions in the TbCl3(AlCl3)x(g) complex system have been analyzed according to the Judd–Ofelt theory of forced electric dipole transitions. This represents the first successful attempt to utilize observations of both absorption and fluorescence spectra in establishing the parameters of the theory. The positions of 19 Tb3+ energy levels were determined from the spectra and used to perform a parametric analysis of the Hamiltonian matrix for the ion’s 4f8 configuration. The wave functions obtained in diagonalization of the Hamiltonian were used to calculate unit tensor operator matrix elements required in the intensity analysis. A good fit to the measurements was obtained with intensity parameters W2 = 20.5, W4 = 2.3, and W6 = 3.0 pm2. These results were then used to compute intensities of fluorescence transitions from the higher lying 5D3, 5G6, and 5L10 levels, yielding additional qualitative agreement between theory and experiment. Some of the major discrepancies between theory and experiment may be due to the need for inclusion of odd‐order intensity parameters or J mixing in the Judd–Ofelt theory.