Glass composition dependence of Eu ion red fluorescence

Eu³⁺ ion-doped B₂O₃-, SiO₂-, and P₂O₅-based glasses were prepared by the melt-quenching method, and their absorption, fluorescence, and excitation spectra were recorded and assigned. The glass composition dependence of the fluorescence was investigated to obtain the high brightness of the red fluorescence due to the ⁵D₀→⁷F₂ transition of the Eu³⁺ ion. The integrated intensity of the red fluorescence was the strongest at the Eu₂O₃ concentration of 3.5 mol% because the cross-relaxation (CR) processes, (⁵L₆→⁵D_J^′)→(⁷F_J^*←⁷F_J^#) and (⁵D_J→⁵D_J^′)→(⁷F_J^*←⁷F_J^#) (3≧J>J′≧0, 6≧J^*>J^#≧0) between the Eu³⁺ ions were promoted, but the CR processes, (⁵D₀→⁷F_J^′)→∑_m(⁷F_J^*←⁷F_J^″)_m (6≧J′≧0, 6≧J^*>J^″≧0), between the excited Eu³⁺ ion at the ⁵D₀ level and m ions of Eu³⁺ in the ⁷F_J^″ levels were depressed. The former CR processes, (⁵L₆→⁵D_J^′)→(⁷F_J^*←⁷F_J^#) and (⁵D_J→⁵D_J^′)→(⁷F_J^*←⁷F_J^#) were enhanced in the host glasses consisted of the cations with small ionic radius. In this study, a 70B₂O₃-30CaO-3.5Eu₂O₃ glass showed the strongest red fluorescence.     

Luminescence spectroscopy of rare earth-doped oxychloride lead borate glasses

Ln-doped oxychloride lead borate glasses were studied using luminescence spectroscopy. Rare earth ions were limited to trivalent Pr³⁺, Tm³⁺, Eu³⁺ and Er³⁺. Luminescence spectra were registered, which correspond to ³P₀-³H₄ and ¹D₂-³H₄ transitions of Pr³⁺, ¹G₄-³H₅ and ¹G₄-³F₄ transitions of Tm³⁺, ⁵D₀-⁷F_J (J=0, 1, 2, 3, 4) transitions of Eu³⁺ and ⁴S_3/2,²H_11/2-⁴I_15/2 and ⁴I_13/2-⁴I_15/2 transitions of Er³⁺. Luminescence decays from the excited states of Ln³⁺ ions were analyzed in detail. The experimental results indicate that relatively high phonon energy of the host gives important contribution to the excited state relaxation of rare earth ions.     

Vibronic and Raman spectra of Y(Eu3+) polytantalate, EuxY1?xTa7O19

Luminescence spectra, luminescence excitation spectra, and Raman spectra of polycrystalline Eu_0.9Y_0.1Ta₇O₁₉ were studied. Zero-phonon lines and vibronic sidebands of the ⁷ F ₀−⁵ D ₂ and ⁷ F ₀−⁵ D ₀ transitions were identified and the Stark splittings of several ⁷ F _J and ⁵ D _J , states of Eu³⁺ ions were investigated. The details of the structure of lanthanide polytantalates and the reduction of the luminescence quenching are discussed. Original Text ? Astro, Ltd., 2007.     

Facile synthesis and luminescence properties of uniform and monodisperse KY3F10:Ln3+ (Ln=Eu,Ce, Tb) nanospheres

Highly uniform and monodisperse KY₃F₁₀:Ln³⁺ (Ln=Eu, Ce, Tb) nanospheres, with an average diameter of 300 nm, have been successfully prepared through a simple template-free and surfactant-free stirring method under ambient conditions. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectra were used to characterize the samples. The SEM images illustrate that these spheres were actually composed of randomly aggregated nanoparticles. The doped rare earth ions show their characteristic emission in the KY₃F₁₀ samples, i.e., Eu^{3+ 5}D₀–⁷F_J (J=1, 2, 3, 4), Tb^{3+ 5}D₄–⁷F_J (J=6, 5, 4, 3, 2) and Ce³⁺ 5d–4f transition emissions, respectively. An energy transfer phenomenon from Ce³⁺ to Tb³⁺ has been observed in KY₃F₁₀ nanospheres, and the energy transfer efficiency depends on the doping concentration of Tb³⁺ if the concentration of Ce³⁺ is fixed.     

Spectra, energy levels, and symmetry assignments for Stark components of Eu(4f) in gadolinium gallium garnet (Gd3Ga5O12)

Absorption and fluorescence spectra observed between 450 and 750 nm at 85 K and room temperature (300 K) are reported for Eu³⁺(4f⁶) in single-crystal Czochralski-grown garnet, Gd₃Ga₅O₁₂ (GGG). The spectra represent transitions between the ^2S+1L_J multiplets of the 4f⁶ electronic configuration of Eu³⁺ split by the crystal field of the garnet. In absorption, Eu³⁺ transitions are observed from the ground state, ⁷F₀, and the first excited multiplet, ⁷F₁, to multiplet manifolds ⁵D₀, ⁵D₁, and ⁵D₂. The Stark splitting of the ⁷F_J multiplets (J=0-6) was determined by analyzing the fluorescence transitions from ⁵D₀, ⁵D₁, and ⁵D₂ to ⁷F_J. The Eu³⁺ ions replace Gd³⁺ ions in sites of D₂ symmetry in the lattice during crystal growth. Associated with each multiplet manifold are 2J+1 non-degenerate Stark levels characterized by one of four possible irreducible representations (irreps) assigned by an algorithm based on the selection rules for electric-dipole (ED) and magnetic-dipole (MD) transitions between Stark levels in D₂ symmetry. The quasi-doublet in ⁵D₁ was characterized by an analysis of the magneto-optical spectra obtained from the transitions observed between ⁵D₁ and ⁷F₁. A parameterized Hamiltonian defined to operate within the entire 4f⁶ electronic configuration of Eu³⁺ was used to model the experimental Stark levels and their irreps. The crystal-field parameters were determined through use of a Monte-Carlo method in which nine independent crystal-field parameters, were given random starting values and optimized using standard least-squares fitting between calculated and experimental levels. The final fitting standard deviation between 57 calculated-to-experimental Stark levels is 5.9 cm⁻¹. The choice of coordinate system, in which the nine are real and the crystal-field z-axis is parallel to the [0 0 1] crystal axis and perpendicular to the xy plane, is identical to the choice we used previously in analyzing the spectra of Er³⁺ and Ho³⁺ garnets.     

Luminescence Properties of Dual Valence Eu Doped Nano-crystalline BaF2 Embedded Glass-ceramics and Observation of Eu2+ → Eu3+ Energy Transfer

Europium doped glass-ceramics containing BaF₂ nano-crystals have been prepared by using the controlled crystallization of melt-quenched glasses. X-ray diffraction and transmission electron microscopy have confirmed the presence of cubic BaF₂ nano-crystalline phase in glass matrix in the ceramized samples. Incorporation of rare earth ions into the formed crystalline phase having low phonon energy of 346 cm⁻¹ has been demonstrated from the emission spectra of Eu³⁺ ions showing the transitions from upper excitation states ⁵D_J (J = 1, 2, and 3) to ground states for the glass-ceramics samples. The presence of divalent europium ions in glass and glass-ceramics samples is confirmed from the dominant blue emission corresponding to its 5d-4f transition under an excitation of 300 nm. Increase in the reduction of trivalent europium (Eu³⁺) ions to divalent (Eu²⁺) with the extent of ceramization is explained by charge compensation model based on substitution defect mechanisms. Further, the phenomenon of energy transfer from Eu²⁺ to Eu³⁺ ion by radiative trapping or re-absorption is evidenced which increases with the degree of ceramization. For the first time, the reduction of Eu³⁺ to Eu²⁺ under normal air atmospheric condition has been observed in a BaF₂ containing oxyfluoride glass-ceramics system.     

Optical absorption and photoluminescence studies of Eu-doped phosphate and fluorophosphate glasses

Phosphate (P₂O₅+K₂O+BaO+Al₂O₃+Eu₂O₃) and fluorophosphate (P₂O₅+K₂O+BaO+BaF₂+Al₂O₃+Eu₂O₃) glasses with different Eu³⁺ ion concentrations have been prepared and characterized through optical absorption, photoluminescence and decay times. An intense red luminescence is observed from the ⁵D₀ emitting level of Eu³⁺ ions in these glasses. The relative luminescence intensity ratio of ⁵D₀→⁷F₂→⁵D₀→⁷F₁ transitions has been evaluated to estimate the local site symmetry around the Eu³⁺ ions. The emission spectra of these glasses show a complete removal of degeneracy for the ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transitions. Second and fourth rank crystal-field (CF) parameters have been calculated together with the CF strength parameter by assuming the C_2v symmetry for the Eu³⁺ ions in both the phosphate and fluorophosphate glasses. Judd-Ofelt parameters have been evaluated from the luminescence intensity ratios of ⁵D₀→⁷F_J (J=2, 4 and 6) to ⁵D₀→⁷F₁ transitions. These parameters have been used to derive radiative properties such as transition probabilities, branching ratios, radiative lifetimes and peak stimulated emission cross-sections for the ⁵D₀→⁷F_J transitions. Decay curves of the ⁵D₀ level of Eu³⁺ ions in these two Eu³⁺:glass systems have been measured by monitoring the ⁵D₀→⁷F₂ transition (611 nm) at room temperature. The experimental lifetime of the ⁵D₀ level in the title glasses is found to be higher than Eu³⁺-doped niobium phosphate glasses. The analysis indicates that the lifetime of the ⁵D₀ level is found to be less sensitive to the Eu³⁺ ion concentration and addition of BaF₂ has no significant effect on the optical properties of Eu³⁺-doped phosphate glasses.     

Cooperative absorption in Eu2O2S

Lines due to cooperative optical absorption of Eu³⁺ have been observed in the luminescence excitation spectra for Eu₂O₂S at 75 K. A pair of Eu³⁺ ions are simultaneously excited by one photon to the ⁵D_J and ⁷F'_J states from the ground state ⁷F₀. Estimated oscillator strengths of the pair absorption are of the order of 10^-9, and are much larger than those in other rare earth compounds reported elsewhere. Multipolar interaction between Eu³⁺ ions cannot explain such a large oscillator strength. Hole-exchange through the charge transfer state, or a super-exchange mechanism, gives a reasonable order of the pair absorption strength in Eu₂O₂S.     

Photophysics of RbCl co-doped with Eu2+ and Eu3+

Excitation and luminescence spectra of RbCl co-doped with divalent and trivalent europium ions are reported. Spectral dips appearing in the blue emission from Eu²⁺ are resulted from the radiative energy transfer from Eu²⁺ to Eu³⁺ and consequently induces the luminescence from Eu³⁺ that is responsible for the ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4) transitions. The induced luminescence has been characterized as a function of temperature and a decay time. In addition, the polarized emission from RbCl doped with only Eu²⁺ is also reported.     

Temperature dependence of the luminescence of Li6Gd x Y1 ? x (BO3)3:Eu crystals

The luminescence and recombination processes in crystals of lithium borates Li₆Gd _x Y_{1 ? x} (BO₃)₃:Eu (LGYBO:Eu) have been studied. The photoluminescence (PL) spectra upon selective photoexcitation to lower excited states of Gd³⁺ and Eu³⁺ ions and the temperature dependences of the photoluminescence intensity at different energies of excitation photons have been measured in a wide temperature range: 10?C500 K. We observed a photoluminescence band at 3.97 eV, which is due to the ⁶ P _J ?? ⁸ S _7/2 transitions in Gd³⁺ ions, and a characteristic line spectrum in the range of 1.6?C2.2 eV, which is related to the radiative f-f transitions in impurity Eu³⁺ ions, occurring mainly from the lower excited ⁵ D ₀ level to the ⁷ F _J states (J = 0, 1, ??, 6). The influence of the O-Eu charge transfer states and the vibrational relaxation between the ⁶ I _J and ⁶ P _J levels of the Gd³⁺ ion on the temperature dependences of the intrinsic and impurity luminescence intensities is discussed.     

Excitation and luminescence of rare earth-doped lead phosphate glasses

Excitation and luminescence properties of Eu³⁺, Tb³⁺ and Er³⁺ ions in lead phosphate glasses have been studied. From excitation spectra of Eu³⁺ ions, the electron–phonon coupling strength and phonon energy of the glass host were calculated and compared to that obtained by Raman spectroscopy. Main intense and long-lived luminescence bands are related to the ⁵D₀–⁷F₂ (red) transition of Eu³⁺, the ⁵D₄–⁷F₅ (green) transition of Tb³⁺ and the ⁴I_13/2–⁴I_15/2 (near-infrared) transition of Er³⁺. The critical transfer distances, the donor–acceptor interaction parameters and the energy transfer probabilities were calculated using the fitting of the luminescence decay curves from ⁵D₀ (Eu³⁺), ⁵D₄ (Tb³⁺) and ⁴I_13/2 (Er³⁺) excited states. The energy transfer probabilities for Eu³⁺ (⁵D₀), Tb³⁺ (⁵D₄) and Er³⁺ (⁴I_13/2) are relatively small, which indicates low self-quenching luminescence of rare earth ions in lead phosphate glasses.     

Photoluminescence properties of Eu-doped ZnO films grown by sputtering-assisted metalorganic chemical vapor deposition

Photoluminescence (PL) properties of Eu-doped ZnO (ZnO:Eu) grown by a sputtering-assisted metalorganic chemical vapor deposition technique were investigated. In PL measurements at 300 K, the samples annealed at 600 °C for 30 min showed clear red-emission lines due to the intra-4f shell transition of ⁵D₀→⁷F_J (J=0–4) in Eu³⁺. In photoluminescence excitation (PLE) spectra, the PL was observed under the high-energy excitation above the band-gap energy of ZnO (indirect excitation) and the low-energy excitation resonant to the energy levels of ⁷F₀–⁵D₃ and ⁷F₀–⁵D₂ transitions in Eu³⁺ (direct excitation). The PL lifetime under the indirect excitation was shorter than that under the direct excitations. These PL properties revealed that the energy transfer from ZnO host to Eu³⁺ was accompanied under indirect excitation.     

Sol-gel synthesis and photoluminescence of CaSiO3:Eu nanophosphors using novel silicate sources

In this paper, seven kinds of silane coupling reagents were employed as silicate sources to prepare CaSiO₃:Eu³⁺ phosphors by the sol-gel method. The different silicate precursors were used to adjust the microstructure and size of the resulting phosphors. The crystallite size of phosphors is in the range of 30-35 nm and some of them show regular microstructure after high-temperature thermolysis. The photoluminescence properties show that all of them exhibit the characteristic fluorescence ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4) of the Eu³⁺ ion and the strongest one is the red emission at 610 nm. Furthermore, the emission quantum efficiency (η) of the ⁵D₀ Eu³⁺ excited state has been calculated to be around 33% from the emission spectrum and the lifetime of the Eu³⁺ first excited level (τ, ⁵D₀).     

Laser spectroscopy of Eu<Superscript>3+</Superscript> cubic centers in the CaF<Subscript>2</Subscript> bulk single crystal

The optical transitions ⁵ D _{0, 1} → ⁷ F _J (J = 0, 1, ..., 6) of Eu³⁺ cubic centers in the CaF₂ single crystal are investigated using combined excitation and emission spectroscopy at different time delays after the excitation pulse. The energies of the Stark sublevels of the ⁷ F _J ground states are determined.     

Effect of modifier oxides on absorption and emission properties of Eu doped different lithium fluoroborate glass matrices

Eu³⁺ doped lithium fluoroborate glass with different modifier oxides (Li₂B₄O₇–BaF₂–NaF–MO where M=Mg, Ca, Cd and Pb) and combinations of modifier oxides (Li₂B₄O₇–BaF₂–NaF–MgO+CaO, Li₂B₄O₇–BaF₂–NaF–CdO+PbO) were prepared by means of melt quenching method. These glass samples were analyzed by absorption, photoluminescence and decay curve measurements. The relative merits of thermal correction to the spectral intensities originating from the ground state (⁷F₀) of different absorption bands of Eu³⁺ are calculated. From the optical absorption measurements and using the Judd–Ofelt (J–O) theory, J–O parameters (Ω_λλ=2, 4 and 6) have been obtained which are used to predict the radiative properties such as radiative transition probabilities (A), radiative life-times (τ_R), and branching ratios (β_r) for certain transitions in all the glass matrices. From the emission spectra, peak stimulated emission cross-sections (σ_P) are obtained for the emission transitions, ⁵D₀→⁷F₁, ⁵D₀→⁷F₂, ⁵D₀→⁷F₃ and ⁵D₀→⁷F₄ of Eu³⁺ in lithium fluoroborate glass matrix with different modifier oxides. The fluorescence decay curves of the ⁵D₀→⁷F₂ transition have been measured and analyzed for all the glass matrices.     

Eu3+ Doped CaWO4—A Potential Red Long Afterglow Phosphor

In this study, a series of Eu³⁺ doped CaWO₄ phosphors were synthesized by the solid-state reaction method. Red long afterglow was observed after samples were excited with 254 nm. The main emission peaks were ascribed to the ⁵D₀–⁷F _J (J=0, 1, 2, 3, 4) transitions of Eu³⁺, and the duration of the optimal sample could last nearly 40 min in the dark seen with naked eyes. The effect of the doping concentration of Eu³⁺ and alkali metal charge compensators (Li, Na, K) on the luminescent properties of the products were investigated in detail. The proposed mechanism of this afterglow property is also discussed.     

Synthesis and luminescent properties of Y6W2O15:Eu phosphors

In this paper, a novel phosphor, Y₆W₂O₁₅:Eu³⁺ was synthesized by thermal decomposition and phase transition of its decatungstate gel precursor. With stepwise increase of temperature to 750 °C, a crystalline phase of Y₆W₂O₁₅:Eu³⁺forms that gives intense red emission when excited at 466 nm, the emission is attributed to the Eu³⁺ ions transitions from ⁵D₀ excited states to ⁷F_J (J=0-4) ground states. The long excitation wavelength proves the Eu³⁺ transition follows the photoexcitation of the oxygen-metal (O→W lmct) charge transfer bands in yttrium tungstate. Some structural information regarding Y₆W₂O₁₅ provided by luminescence is in accord with that characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The long-wavelength excitation properties of this material may find application in the production of red phosphors for white light-emitting diodes (LEDs).     

Photoluminescence properties of rare earth doped α-Si3N4

The photoluminescence properties of Eu²⁺, Ce³⁺ and Tb³⁺ doped α-Si₃N₄ have been studied and a possible structural model has been proposed on the basis of the Rietveld refinement of X-ray powder diffraction data. Nearly single phase rare earth doped α-Si₃N₄ was synthesized by a solid state reaction at 1600 °C in N₂-H₂ atmosphere starting from amorphous Si₃N₄ and rare earth oxides or nitrides. Because of small crystal field splitting of the 5d levels, the excitation and emission bands of Eu²⁺ and Ce³⁺ are positioned at higher energies as isolated ions in comparison with that in Ca-α-Sialon. Both Eu²⁺- and Ce³⁺-doped α-Si₃N₄ show blue band emission peaking at about 470 and 450 nm, respectively, under UV excitation. α-Si₃N₄:Tb³⁺ exhibits dominant green line emission mainly arising from ⁵D₄→⁷F_J (J=6-3) with weak ⁵D₃→⁷F_J (J=6-3) transitions of Tb³⁺ when excited by UV light. The thermal stability of α-Si₃N₄:Eu²⁺ is comparable with that of Ca-α-Sialon:Eu²⁺ and is much better than that of α-Si₃N₄:Ce³⁺.     

Photoluminescence of Eu-doped ZnAl-LDH depending on phase transitions caused by annealing temperatures

An Eu-doped ZnAl-layered double hydroxide (ZnAl-LDH) was synthesized by the coprecipitation method at room temperature. A set of as-prepared samples were subjected to annealing at various temperatures from 100, 200, 300, 500, 600, 700, to 800 °C for 1 h, respectively. The annealed samples were characterized by powder X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscope (SEM), and photoluminescence (PL). New phases occurred with annealing temperatures above 300 °C. Meanwhile, the emissions of Eu³⁺ ions described by ⁵D₀-⁷F_J transition (J=1, 2, 3, 4), especially for the ⁵D₀-⁷F_J transition (J=1, 2), varied with phase transitions of its local host materials from ZnAl-LDH, ZnO, to mixed phases of ZnO and ZnAl₂O₄. The emissions of Eu³⁺ ions depending on its host materials were discussed.     

Optical properties of red, green and blue emitting rare earth benzenetricarboxylate compounds

Red, blue and green emitting rare earth compounds (RE³⁺=Eu³⁺, Gd³⁺ and Tb³⁺) containing the benzenetricarboxylate ligands (BTC) [hemimellitic (EMA), trimellitic (TLA) and trimesic (TMA)] were synthesized and characterized by elemental analysis, complexometric titration, X-ray diffraction patterns, thermogravimetric analysis and infrared spectroscopy. The complexes presented the following formula: [RE(EMA)(H₂O)₂], [RE(TLA)(H₂O)₄] and [RE(TMA)(H₂O)₆], except for Tb-TMA compound, which was obtained only as anhydrous. Phosphorescence data of Gd³⁺-(BTC) complexes showed that the triplet states (T) of the BTC³⁻ anions have energy higher than the main emitting states of the Eu³⁺ (⁵D₀) and Tb³⁺ (⁵D₄), indicating that BTC ligands can act as intramolecular energy donors for these metal ions. The high values of experimental intensity parameters (Ω₂) of Eu³⁺-(BTC) complexes indicate that the europium ion is in a highly polarizable chemical environment. Based on the luminescence spectra, the energy transfer from the T state of BTC ligands to the excited ⁵D₀ and ⁵D₄ levels of the Eu³⁺ and Tb³⁺ ions is discussed. The emission quantum efficiencies (η) of the ⁵D₀ emitting level of the Eu³⁺ ion have been also determined. In the case of the Tb³⁺ ion, the photoluminescence data show the high emission intensity of the characteristic transitions ⁵D₄→⁷F_J (J=0-6), indicating that the BTC ligands are good sensitizers. The RE³⁺-(BTC) complexes act as efficient light conversion molecular devices (LCMDs) and can be used as tricolor luminescent materials.