Luminescence quenching of cyclometalated Pt(II) complexes by halogenide ions

The luminescence quenching of [Pt(CΛN)En]ClO₄ complexes ((CΛN)^? = ppy^?, tpy^?, and bt^? are deprotonated forms of 2-phenylpyridine, 2(2′-thienyl(pyridine), and 2-phenylbenzothiazole, respectively; En is ethylenediamine) by halogenide ions (Hal^? = Cl^?, Br^?, I^?) in ethanol solutions is studied. It is shown that the quenching has a dynamic character and its bimolecular rate constants are consistent with the enhancement of nonradiative deactivation of the excited state of {[Pt(CΛN)En]*...Hal} collision complexes with increasing spin-orbit interaction constant of the halogen.     

Luminescence of photochromic centers in calcium fluoride crystals doped with Lu3+ ions

We report data on the luminescence spectra associated with photochromic centers in X-ray irradiated calcium fluoride crystals doped with Lu ions. Irradiation in low energy photochromic centers absorption band excites emission, which can be identify with transitions into photochromic centers. Ab initio calculation of absorption spectrum of photochromic center agrees rather well with experimental data.     

Luminescence centers in porous silicon

Photoluminescence studies on porous silicon show that there are luminescence centers present in the surface states. By taking photoluminescence spectra of porous silicon with respect to temperature, a distinct peak can be observed in the temperature range 100–150 K. Both linear and nonlinear relationships were observed between excitation laser power and the photoluminescence intensity within this temperature range. In addition, there was a tendency for the photoluminescence peak to red shift at low temperature as well as at low excitation power. This is interpreted as indicating that the lower energy transition becomes dominant at low temperature and excitation power. The presence of these luminescence centers can be explained in terms of porous silicon as a mixture of silicon clusters and wires in which quantum confinement along with surface passivation would cause a mixing of andX band structure between the surface states and the bulk. This mixing would allow the formation of luminescence centers.     

Luminescence properties of lanthanide(III) ions in concentrated carbonate solution

Luminescence properties of lanthanide(III) ions (Ln = Nd, Sm, Eu, Gd, Tb, Dy and Tm) were investigated by measuring the excitation and emission spectra, and emission lifetimes in H₂O and D₂O solutions of 3 moll^?1 K₂CO₃, where anionic tetra-carbonate complexes, [Ln(CO₃)₄]^5- were the predominant species.

Electronic transitions of the carbonato complex corresponding to both the excitation and emission spectra were assigned from the energy level diagrams of Ln(III) and compared with those of the aqua ion. Enhancement of emission intensity of the complex was observed at particular excitation transitions of Eu(III), Gd(III) and Tb(III), and at particular emission transitions of Sm(III), Eu(III), Dy(III) and Tm(III). The enhancement at the emission transition was estimated quantitatively as a branching ratio from the lowest emitting state of Ln(III), and discussed in terms of hypersensitivity.

Emission lifetimes of the carbonato complexes were all longer than those of aqua ions in H₂O solution, while the lifetimes of the complexes for Eu(III) and Tb(III) shorter than those in D₂O solution. The difference in non-radiative decay constants for the excited complex in H₂O and D₂O solutions was found to be proportional to an exponential of the energy gap of Ln(III). The lifetime ratio between the H₂O and D₂O solutions showed the order of Sm > Dy > Eu > Tb, corresponding to the opposite order of the energy gap. These were discussed in terms of an energy gap law, i.e. a relationship between the energy gap of Ln(III) and vibration energies of the ligand or water molecules.     

Luminescence centers in cubic boron nitride

Complex and multiband photoluminescence spectra for GB and HBN centers in single crystals of cubic boron nitride (cBN) were recorded in the wavelength ranges 385–400 nm and 365–395 nm and the nature of these centers was studied. The use of models involving resonance vibrations and strongly shifted configuration diagrams for the electronic ground state and excited state made it possible to associate formation of the GB-1 center with the presence of tungsten impurity in cBN. It was established that the HBN band in the 300–350 nm range of the cathodoluminescence spectra of cBN polycrystals, single crystals, and micropowders is associated with luminescence centers present in microinclusions of graphite-like boron nitride (hBN). The nature of the hBN band is tentatively interpreted within the model of recombination of donor and acceptor defects in hBN: respectively nitrogen vacancies and carbon atoms in positions substituting for nitrogen. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 241–246, March–April, 2007.     

Luminescence centers in bismuth-containing oxytungstate ceramics

We have studied the photoexcitation and luminescence spectra of Bi₂WO₆, Y₂WO₆ and Y₂WO₆:Bi ceramics. We used the Alentsev-Fock method to decompose the spectra into elementary components. The emission bands with maximum at 2.93 eV in the luminescence spectrum of Bi₂WO₆, 3.02 eV in the luminescence spectrum of Y₂WO₆, and 2.95 eV in the luminescence spectrum of Y₂WO₆:Bi are assigned to luminescence of self-localized Frenkel excitons. The bands with maxima at 2.35 eV and 1.90 eV in the spectrum of Bi₂WO₆, 2.25 eV and 1.75 eV in the spectrum of Y₂WO₆, and 2.35 eV and 1.85 eV in the spectrum of Y₂WO₆:Bi are connected with oxygen vacancies. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 688–691, September–October, 2007.     

Magnetic ordering in manganites substituted by chromium ions

NdMn_1?x Cr _x O₃ and Nd_0.6Ca_0.4Mn_1?x Cr _x O₃ solid solutions have been studied by neutron diffraction and magnetic measurements. NdMn_0.5Cr_0.5O₃ is found to have a magnetic structure consisting of an antiferromagnetic G-type component and a ferromagnetic component, which are caused by 3d ions. The magnetic moments of the neodymium ions are parallel to the ferromagnetic component. Nd_0.6Ca_0.4Mn_0.5Cr_0.5O₃ mainly has a G-type magnetic structure, and the magnetic moments of the neodymium ions are normal to the antiferromagnetism vector. Magnetic phase diagrams are plotted for both systems. They are interpreted on the assumption that the Mn³⁺-O-Cr³⁺ superexchange interactions are positive and the Mn⁴⁺-O-Cr³⁺ interactions are negative; the fact that manganese and chromium ions are not ordered in a crystal lattice is taken into account. Concentration magnetic phase transformations proceed through a two-phase state because of the internal chemical inhomogeneity of the solid solutions.     

Luminescence centers in silicate and germanate glasses activated by bismuth

Concentration series of silicate and germanate glasses activated by bismuth are studied. It is shown that luminescence in the IR region is controlled by several active centers related to bismuth. Based on a comparison of spectroscopic characteristics of the studied glasses with the data previously obtained for chloride glass, the observed centers were identified as Bi⁺, Bi ₂ ⁴⁺ , and Bi ₅ ³⁺ in germanate glass and Bi⁺, Bi ₂ ⁴⁺ in silicate glass.     

Trigonal chromium centers in zinc sulfide

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 50, No. 4, pp. 624–627, April, 1989.     

The effect of temperature on the luminescence spectra of potassium-aluminum borate and silicate glasses with copper(I) and silver ions

Luminescence and luminescence-excitation spectra of potassium-aluminum borate glasses containing copper(I) and silver ions have been investigated in the temperature range of 20–300°C. It is shown that the luminescence thermochromic effect, which manifests itself in a blue spectral shift of the luminescence bands with an increase in temperature, occurs in glasses of all types, reaching a value of 100 nm. Heating leads to a red shift of luminescence-excitation bands by 20 nm and their broadening. Luminescence quenching occurs in glasses exhibiting photochromic effect at room temperature. An increase in temperature leads to weakening and, finally, disappearance of the photochromic effect in these glasses with subsequent occurrence of the luminescence thermochromic effect.     

Luminescence centers in Sc2O3

Sc₂O₃ luminescence spectra are studied. The spectra are separated into elementary bands by the Alentsev–Fock method. It is established that the luminescence spectra consist of a number of overlapping bands with maxima at 3.5; 3.05; 2.65; 2.35, and 2.05 eV. The band at 3.5 eV is interpreted as emission of self-localized excitons, and the other bands, as defect-center recombination. L’vov State University, 50, Dragomanov St., L’vov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 776–778, November–December, 1997.     

Luminescence of tungsten centers in zinc selenide

Luminescence spectra of W centers in ZnSe are studied. Radiative d–d transitions are identified by the Tanabe–Sugano diagram of the crystal field theory. It is found that the type of electronic transitions changes with a significant change in spectral characteristics of impurity radiation during the transition fromthe 3d- to 5d-electronic systemof impurity centers in the crystals under study.     

Luminescence centers in yttrium silicate and germanate

Luminescence spectra for isostructural Y₂SiO₅ and Y₂GeO₅ are investigated. The spectra are resolved into elementary components by the Alentsev—Fock method. Bands with maxima in regions of 2.6, 2.3, and 2.05 eV in the spectra of Y₂SiO₅ luminescence and in regions of 2.55, 2.25, and 2.0 eV in the spectra of Y₂GeO₅ luminescence are considered as radiative recombination of excited associative donor-acceptor Y³⁺−O²⁻ pairs. The indicated bands are related to certain distances between yttrium (the donor) and oxygen (the acceptor). A band with a maximum of 2.95 eV in Y₂SiO₅ and 3.0 eV in Y₂GeO₅ occurs in recombination of electrons with holes trapped by an anionic sublattice. I. Franko L’vov State University, 50, Dragomanov St., L’vov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 528–531, July–August, 1998.     

Luminescence of enrichment centers in yttrium-aluminum garnet crystals

The spectrum of enrichment centers in yttrium-aluminum garnet crystals is studied. Analysis of the photoluminescence and excitation spectra together with measurements of luminescence kinetics allow establishment of the energy structure of the centers found.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 83–87, January, 1984.