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Single crystal of bismuth tellurite Bi2TeO5 (BTO) doped with trivalent thulium (Tm3+) was grown by the Czochralski method and investigated by spectroscopic techniques (absorption, emission). Absorption and emission of the Tm:BTO crystal collected in the VIS-IR spectral range are presented. Spectroscopic features were investigated as a function of the excitation light polarisation (E//X, Y, and Z axis of optical indicatrix) and sample temperature. The oscillator strength of the 3H6 → 3F4 transition at 1.7 μm was determined by numerical integration of the X, Y and Z polarised absorption spectra. The obtained values are: PX = 4.7 × 10−6, PY = 6.8 × 10−6 and PZ = 5.9 × 10−6 that gives a mean value Pmean = 5.8 × 10−6. Emission was observed from the 1G4 and 3H4 levels. The 3H4 and 1G4 excited state dynamics was studied. Decay curves and time constants of luminescence were collected at 5 and 300 K and analysed. The 3F4 → 3H6 luminescence at around 1.8 μm was too weak to be acquired from the low concentrated sample. However, based on optical data it was possible to estimate the radiative probability Arad of this transition and the 3F4 radiative lifetime. The resultant values are: Arad = 668 ± 0.4 s−1 and τrad = 1.5 ms. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Single crystals of GdCa4O(BO3)3 (GdCOB) pure and doped with Eu concentration of 1 and 4 at% were grown by the Czochralski and micropulling-down methods. The distribution of Eu ions in GdCOB crystals was uniform. The substitutions of Eu3+ in Gd, Ca(1) and Ca(2) cation sites and eventually formation Eu2+ have been investigated. The spectroscopic properties of crystals are compared with the properties of nanopowders obtained by sol-gel method. Radioluminescence spectra of undoped GdCOB crystal show the characteristic emission of Gd3+ at about 312 nm, whereas this emission dramatically decreases in Eu-doped crystals upon X-ray excitation, as well as in Eu-doped nanopowders excited in vacuum ultraviolet (VUV) region. The VUV excitation in the range 125-333 nm for Eu-doped samples leads to strong emission in red coming from the 5D0 multiplet of Eu3+, only. In the photoluminescence decay kinetics of 312 nm emissions substantial shortening and departure for single exponential decay in Eu-doped samples is clearly observed. Higher Eu doping results in further acceleration of the decay. In undoped GdCOB crystal, the lifetime of the Gd3+6P7/2 multiplet is 2.79 ms. The Eu3+5D0 decay kinetics monitored at 613 nm are rather constant. Numerical fitting of fully exponential curves, reveals lifetimes 2.7 ms for nanopowder and 2.5 ms for single crystal. The results suggest that this material may be used as a red phosphor in plasma display panels in nanopowder form because of strong excitation band of Eu3+ luminescence in the 160-200 nm regions. Contrary to nanopowder sample, such an excitation band, attributed to the Gd3+–O2– charge transfer was not observed in crystal obtained by the micropulling-down method. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Trivalent impurity ions are clustered easily in fluoride crystals. With the addition of Y3+ spectral properties are greatly enhanced. Low temperature absorption and emission spectra are performed to unfold the optical centers in Nd3+,Y3+:CaF2 crystals. The strongest absorption line at around 790 nm belongs to M luminescence quenched centers in 1%Nd3+:CaF2; and at 797 nm to L′ centers for a codoped one. For emission spectra 1049.3 nm and 1068.7 nm are attributed to M′ and N′ non quenched centers; 1054.6 nm to an L′ site in a 1%Nd3+,5%Y3+:CaF2 sample. EXAFS spectra, an intuitive approach, are applied to reveal that the first coordination number of Nd3+ increased from 9.2 to 10.7 with the addition of Y3+ ions, and the local lattice expanded. [ABSTRACT FROM AUTHOR]