Wide Excitation Band Research Articles

A europium(III) organic ternary complex applied in fabrication of near UV-based white light-emitting diodes

A β-diketone, 2-acetylfluorene-4,4,4-trifluorobutane-1,3-dione (HAFTFBD), and its three europium(III) complexes, Eu(AFTFBD)3⋅2H2O, Eu(AFTFBD)3(TPPO)2 and Eu(AFTFBD)3phen, were designed and synthesized, where TPPO was triphenylphosphine oxide and phen was 1,10-phenanthroline. The complexes were characterized by IR, UV-visible, photoluminescence (PL) spectroscopy and thermogravimetric analysis (TGA). The results show that the Eu(III) complexes exhibit a high thermal stability,and wide and strong excitation bands when monitored at 613 nm. Excited by ∼395 nm near UV light, the complexes emitted strong and characteristic red light due to f–f transitions of the central Eu3+ ion, and no emission from the ligands was found. The photoluminescence mechanism of the europium(III) complexes was investigated and proposed as a ligand-sensitized luminescence process. Among the three europium(III) complexes, Eu(AFTFBD)3phen exhibits the highest thermal stability and the most excellent photoluminescence properties. A bright red light-emitting diode was fabricated by coating the Eu(AFTFBD)3phen complex onto an ∼395 nm-emitting InGaN chip, and the LED showed appropriate CIE chromaticity coordinates (x=0.66, y=0.33). A white LED with CIE chromaticity coordinates (x=0.32, y=0.32) was prepared with Eu(AFTFBD)3phen as red phosphor, indicating that Eu(AFTFBD)3phen can be applied as a red component for fabrication of near ultraviolet-based white light-emitting diodes.

Optical spectroscopy of europium 3,5-dinitrosalicylates—Intense red luminophores

It was found, that alkali metal-europium dinitrosalicylates of composition M 3Eu(3,5-NO 2-Sal) 3· nH 2O (M = Li, Na, K, Cs) are intense red luminophores with wide excitation band. Using methods of optical spectroscopy we studied the influence of nitrogroups and alkali metal counterions on Eu 3+ luminescence efficiency and on processes of excitation energy transfer to Eu 3+ ion in compounds synthesized. The Eu 3+ luminescence and Eu 3+ luminescence excitation spectra, as well as vibrational IR and Raman spectra were investigated. Details of the structure of compounds were discussed. The network of hydrogen bonds in lanthanide dinitrosalicylates is weakening at introduction of large alkali metal ions in compounds and at the increase of the temperature. As a consequence, the long-wavelength shift of the intraligand charge transfer (ILCT) band in Eu 3+ excitation spectra arises at inclusion of Cs + cations instead of Li + in the crystal lattice of europium dinitrosalicylates and at heating of these compounds. To obtain the energy of the lowest excited triplet state the phosphorescence spectra of alkali metal-gadolinium compounds M 3Gd(3,5-NO 2-Sal) 3· nH 2O, of alkali metal dinitrosalicylate and salicylate salts were measured with time delay. Change of the energies of ligand electronic states and ligand–metal charge transfer state (LM CTS) can give a two-three orders of magnitude enhancement of the Eu 3+ luminescence efficiency in dinitrosalicylates in comparison with salicylates and ten-fold enhancement at the substitution of Li + and Na + for Cs + in dinitrosalicylates.

Defect Mediated and Resonant Optical Excitation of Er3+Ions in Silicon-rich Silicon Oxide

AbstractWe study sensitization of the4I13/2–4I15/2Er3+luminescence at 1.54 μm in silicon-rich silicon oxide (SRSO) in the whole range of blue-green pump wavelengths. We show that, in general, defects due to excess Si in silica act as luminescence sensitizers. They cause a wide excitation band with a long wave length limit of 600 nm. For monochromatic excitation the maximum luminescence yield is still smaller than for resonant excitation within the 4f shell of Er without additional Si. The large enhancement of the excitation cross section for electrical excitation reported in the literature is plausible, however, as the wide excitation band makes good use of the wide energy distribution of hot carriers. We suggest that the dominant factors, which limit the excitation efficiency of Er3+, are distance dependence of the transfer rate and little spectral overlap of the interacting states.

Photoluminescence of concentration series of CaF2: Mn phosphors excited by VUV radiation

Fluorescent characteristics of a series of powder CaF2: Mn phosphors (from 0.01 to 2.47 wt. % of Mn in the mixture) excited by VUV radiation with quantum energies up to 14 eV at 293 K and up to 12 eV at 85 K are measured. Narrow excitation bands of Mn2+ centers found at 7.9 and 8.6 eV (at 293 K) are assigned to partially forbidden transitions of electrons from the ground state 6S split by the crystalline field (10 Dq=0.71 eV from the literature) in two sublevels to the excited level corresponding to the 6D term of a free Mn2+ ion (3d5 → 3d44s transitions). A wide nonelementary excitation band in the region of 9.1–10.3 eV is interpreted as photogeneration of near-activator D-excitations: allowed transitions of electrons from levels that are split from the top of the valence band under the influence of an impurity ion to the free 4s-orbital of a Mn2+ ion. Channels of energy transport in the CaF2: Mn system are briefly analyzed.

A selective gas chromatographic detector for polynuclear aromatics based on ultraviolet fluorescence

A vapor-phase fluorescence detector for the analysis of mixtures of polynuclear aromatic ring systems has been developed. This system utilizes wide bandpass excitation and wide band emission filters, thus increasing sensitivity and decreasing the complexity of previously designed instruments. The sensitivity of the detector has been demonstrated to be at the nanogram level with reasonable precision.