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Gallium nitride co-doped with magnesium and europium shows great potential for active layers in red light emitting diode structures due to strong and sharp luminescence emission around 620 nm. In this work, sharp and intense Eu3+ luminescence lines from the excited states of the 5D J (J = 0, 1) multiplets to the ground states of the 7F J (J = 0, 1, 2) multiplets have been analyzed using a C 2 v crystal-field equivalent operator Hamiltonian. A model of Eu centers with the C 2 v symmetry has been proposed to be an Eu3+ complex accompanied by either a pair of nitrogen and gallium vacancies (V N - V Ga) or a pair consisting of a nitrogen vacancy and magnesium impurity (V N - Mg Ga) in the vicinity of the Eu ion based on the crystal-field analysis, the selection rules and the observed polarization of the Eu3+ luminescence lines. Energy transfer from the host to the Eu ions under band-to-band excitation occurs through electron-hole recombination between V N with the electron-like state and V Ga or Mg Ga with the hole-like state; these may be associated with the shallow-trapped or deep-trapped states, respectively, proposed as the energy transfer mechanism in previous literature. • Polarized photoluminescence/cascade-luminescence from ex situ Eu-doped GaN(Mg). • Energy levels/states of 7F 0 ,7F 1 and 7F 2 multiplets of Eu3+ experimentally estimated. • Model of Eu centers in GaN(Mg) with C 2 v (orthorhombic) symmetry proposed. • Eu complex with N/Ga vacancy pair, or a pair consisting of N vacancy and Mg impurity. • Energy transfer GaN.→Eu via recombination between these electron-like/hole-like states [ABSTRACT FROM AUTHOR]

In the present study, structural and photo-luminescence studies of Eu 3+ and Tb 3+ co-doped ZnMoO 4 host matrix has been investigated in detail. ZnMoO 4 :Eu 3+ /Tb 3+ have been synthesized via a simple and cost effective co-precipitation method. XRD, Raman and FTIR studies confirmed its triclinic structure of Eu 3+ /Tb 3+ co-doped ZnMoO 4 host. Emission spectra of the measured samples corroborate the dominant electric dipole transition emission ( 5 D 0 - 7 F 2 ) intensity over magnetic dipole transition emission ( 5 D 0 - 7 F 1 ) intensity. Moreover, the improvement in red emission ( 5 D 0 - 7 F 2 ) for Eu 3+ (3 at%) and Tb 3+ (2 at%) and high asymmetric ratio ∼10.4 is observed which dictates it as a highly red emitter. Additionally, commission international de-I′ Eclairage (CIE) values approaches to NSTC. Color purity of red emission improves after Tb 3+ co-doping. Photoluminescence studies reveals that Tb 3+ acts as a sensitizer for the Eu 3+ activated ZnMoO 4 host matrix. Study reveals that Eu 3+ /Tb 3+ co-doped ZnMoO 4 can be excited by near UV device, which is bottleneck in the advancement of LEDs technology. [ABSTRACT FROM AUTHOR]

Controlling of valence states of metal ions doped in glasses has attracted considerable interest due to the possibility of looking toward optical applications. In this study, new Na 2 O-Al 2 O 3 -SiO 2 glasses were developed to dope Eu 2+ and Mn 2+ with well controlled valence states by heating in H 2 gas atmosphere, and the changes in the valence state of doped-ions and their fluorescence properties were investigated using visible and infrared optical absorption spectroscopies, X-ray absorption fine structure spectroscopy, and fluorescence spectroscopy. Among Eu 3+ , Mn 3+ and Mn 2+ ions incorporated in the as-prepared glasses, the Eu 3+ and Mn 3+ ions were reduced to Eu 2+ and Mn 2+ ions, respectively, by heating in H 2 gas and OH bonds were concurrently formed. The fluorescence spectra of glasses heated in H 2 exhibited broad emission bands at 450 and 630 nm wavelength, assigned to the Eu 2+ and Mn 2+ , respectively, ions, in which the fluorescence intensity at 450 nm was observed to decrease with increasing Mn 2+ ion content. The increased fluorescence intensities were analyzed as the energy transfer from Eu 2+ to Mn 2+ ions and the energy transfer efficiency was estimated with a concentration of Eu 2+ and Mn 2+ ions. [ABSTRACT FROM AUTHOR]

Tb 3 + and Eu 3 + single- and double-doped barium borate glasses are analyzed for their temperature-dependent luminescence and energy transfer properties. The glasses are investigated in the temperature range from 15 K to 700 K. The Tb 3 + doped glass has a higher temperature stability than the Eu 3 + doped one. Increasing the temperature leads to an enhanced energy transfer from Tb 3 + to Eu 3 + in the double-doped glass. The energy transfer mechanism is investigated in detail. [ABSTRACT FROM AUTHOR]

A new approach to calculate the effective Ln–Ln energy transfer rates in a doped crystal matrices was proposed and successfully applied to the YVO 4 :Yb 3+ ,Er 3+ upconversion system. This approach is based on the known set of Ln–Ln distances obtained from the crystal structure of the matrix and the probabilities of their occurrence. The non-radiative energy transfer rates were calculated in the intermediate coupling scheme taking into account the shielding of the 4f electrons. The required partial (that is, forced electric dipole-only, lacking the dynamic coupling contribution) Judd–Ofelt Ω λ parameters were calculated using the Simple Overlap Model (SOM). The spectral overlap factor F was estimated from optical absorption measurements. A simplified “one level-one manifold” energy level scheme was applied. The F 7 / 2 4 , H 11 / 2 2 and S 3 / 2 4 states of Er 3+ were treated as an effective level. The set of rate equations containing radiative, non-radiative and energy transfer processes was solved numerically using fourth-order Runge–Kutta method. Both continuous and pulsed excitation modes were simulated. The dependence of the upconversion intensity upon the pump power was found. The simulations resulted in good agreement with the experimental results and provided new insights into the dynamics of the upconversion process and a connection between the macroscopic properties and the microscopic description. [ABSTRACT FROM AUTHOR]

Eu 3+ and Gd 3+ ions co-doped amorphous silica nanorods were prepared using a simple sol–gel method, and their luminescent properties were studied under the excitation of ultraviolet light. X-ray diffraction (XRD), Energy-dispersive X-ray (EDX) spectroscopy, Fourier transform infrared spectrum (FT-IR), Scanning electron microscope (SEM), Transmission electron microscopy (TEM), and Photoluminescence (PL) spectra were employed to characterize the products in detail. The nanorods are uniform and their diameters and lengths are in the range of 200–300 nm and 500–700 nm, respectively. Energy transfer process in Gd 3+ and Eu 3+ co-doped silica, where a ground state of Gd 3+ , 8 S 7/2 , was selectively excited to a 6 I J state under the excitation of 274 nm, was studied in terms of luminescence spectra, which indict that the energy transfer of Gd 3+ –Eu 3+ is efficient. The mechanism of energy transfer from Gd 3+ to Eu 3+ is a resonant transfer, in which electric dipole–dipole interaction plays a leading role. Furthermore, the doping concentration-dependence of Eu 3+ ions on the energy transfer efficiency was also investigated. [ABSTRACT FROM AUTHOR]

Abstract: La2TeO6 nanocrystals doped with Eu3+ ions have been prepared by the Pechini sol–gel process. A total of seven samples obtained with different Eu3+ concentrations (1–7%). The Eu3+ ions are usually taken as probe ions to test the local structure of the lanthanide in solids. Analyzing the luminescence has been shown two different sites for the Eu3+ ions (in good agreement with the crystallographic analysis). Moreover, the luminescence properties have been analyzed as function of the Eu3+ doping concentration in order to study the interaction between these ions. Under direct excitation into the 5D0 level (at 578nm) the corresponding decay curves show a pure exponential character independently of the Eu3+ concentration. However, the decay curves obtained for the 5D1 level becomes non-exponential for the higher doped nanocrystals samples indicating that the energy transfer processes are important. [Copyright &y& Elsevier]