Wojciech A. Pisarski

Visible and infrared spectroscopy of Pr3+ and Tm3+ ions in lead borate glasses

The visible luminescence of Pr3+ and Tm3+ ions in lead borate glasses has been investigated as a function of activator concentration. The Judd–Ofelt analysis and the Inokuti–Hirayama model for energy transfer between activator ions have been applied for investigations of the radiative and non-radiative relaxation of the Pr and Tm excited states. Based on the luminescence decay curve analysis, the concentration quenching of the 1D2 emission of Pr3+ and 1G4 emission of Tm3+ ions has been attributed to cross-relaxation processes. The infrared spectroscopic measurements provide information on structural changes in the borate network initiated by optically active (Pr or Tm) ions. Contrary to the praseodymium ions, the thulium ions play an additional role as a glass-modifier in the PbO–B2O–Al2O3–WO3 composition.

Tri-color upconversion luminescence of Rare earth doped BaTiO 3 nanocrystals and lowered color separation

Upconversion tri-color luminescence of Er(3+)/Tm(3+)/Yb(3+) doped BaTiO3 nanocrystals is observed under the excitation of a 980 nm laser diode. Especially, Er(3+) emission has a considerable contribution to the blue portion of the UC spectra, different from the ever-reported results, in which blue emission originates only from Tm(3+). This realization is beneficial to lower the color separation between blue and green (or red) emissions, in fluorescent labeling. The analysis of excitation power dependence and decay time revealed that blue emission of Er(3+) ion is induced by a dual energy transfer upconversion, while Tm(3+) plays a role of both emitter and activator.

Rare earth-doped lead borate glasses and transparent glass–ceramics: Structure–property relationship

Correlation between structure and optical properties of rare earth ions in lead borate glasses and glass-ceramics was evidenced by X-ray-diffraction, Raman, FT-IR and luminescence spectroscopy. The rare earths were limited to Eu(3+) and Er(3+) ions. The observed BO(3)↔BO(4) conversion strongly depends on the relative PbO/B(2)O(3) ratios in glass composition, giving important contribution to the luminescence intensities associated to (5)D(0)-(7)F(2) and (5)D(0)-(7)F(1) transitions of Eu(3+). The near-infrared luminescence and up-conversion spectra for Er(3+) ions in lead borate glasses before and after heat treatment were measured. The more intense and narrowing luminescence lines suggest partial incorporation of Er(3+) ions into the orthorhombic PbF(2) crystalline phase, which was identified using X-ray diffraction analysis.

Investigation of Eu3+ sites in SrLaGa3O7, SrLaGaO4 and SrLaAlO4 crystals

Abstract Trivalent europium has been used as a probe of symmetry of crystalline sites occupied by rare earth ions and of electron-phonon coupling in crystals belonging to two wide families of compounds with general chemical formulae ABCO 4 and ABC 3 O 7 ( A = Ca , Sr ; B = Y , La - Gd ; C = Al , Ga ). Random distribution of crystallochemically different ions over the lattice sites results in the spread of energy of Eu 3+ excited states in the three matrices, but the site symmetry is preserved in SrLaAlO 4 and SrLaGaO 4 . Strongly perturbed sites behave as one quasicentre with single decay time of luminescence. The multiphonon relaxation rates for the 5 D 2 level of Eu 3+ have been analysed with a point charge nonlinear relaxation mechanism proposed recently. Unusually low electron-phonon coupling in SrLaGaO 4 :Eu 3+ system has been found.

Anisotropy of optical properties of SrLaAlO4 and SrLaAlO4:Nd

Abstract Single crystals of SrLaAlO 4 and SrLaAlO 4 :Nd have been grown by the Czochralski method and their optical properties have been studied in polarized light. The crystals are positive uniaxial, and their birefringence is stable with respect to temperature in the 290 K–520 K temperature region. Undoped crystal is transparent from 240 nm to 7.6 μm. Intensities of absorption and spontaneous emission of Nd 3+ are slightly lower for light polarized perpendicular than those for light polarized parallel to the optical axis. Laser action in SrLaAlO 4 :Nd has been obtained for the first time using a diode laser as a pump. Stimulated emission occurs in the 1073 nm-1080 nm spectral region. Poor laser performance is attributed to the self-quenching of Nd emission.

Optical transitions of Eu 3+ and Dy 3+ ions in lead phosphate glasses

Lead phosphate glasses containing Eu(3+) and Dy(3+) have been studied. Local structure was verified using Fourier transform (FT)-IR spectroscopy. Emission bands of Eu(3+) and Dy(3+) ions in lead phosphate glasses are observed in the visible spectral range, which correspond to 5D0→7F(J) (J=0,1,2,4) and 4F(9/2)→6H(J/2) (J=15,13,11) transitions, respectively. Shorter luminescence decays from excited states of Eu(3+) and Dy(3+0 are due to the presence of PbO in phosphate glass.

Visible luminescence of dysprosium ions in oxyhalide lead borate glasses

Visible luminescence of Dy(3+) ions in oxyhalide lead borate glasses was examined. Luminescence spectra show two intense bands at 480 nm and 573 nm due to (4)F(9/2)→(6)H(15/2) (blue) and (4)F(9/2)→(6)H(13/2) (yellow) transitions of Dy(3+). Luminescence decays from (4)F(9/2) state and yellow-to-blue luminescence intensity ratios (Y/B) were analysed with PbX(2) (X=F, Cl) content. An introduction of PbX(2) to the borate glass results in the increasing of (4)F(9/2) lifetime and the decreasing of yellow-to-blue luminescence intensity ratio, which is due to reduction of covalency between Dy(3+) and O(2-)/X(-) ions.

Passive mode locking of a Nd3+:SrLaGa3O7 laser

A Nd3+:SrLaGa3O7 laser with a pentacarbocyanine dye cell produced regular 25–30 ps pulses over the period of the flash lamp. Output energy as a function of mirror reflectivity and lamp energy was also determined.

Influence of BaF2 and activator concentration on broadband near-infrared luminescence of Pr3+ ions in gallo-germanate glasses.

Thermal stability and broadband NIR luminescence of Pr(3+) doped gallo-germanate glasses with BaF2 have been studied. The thermal factors are larger for glass samples with low BaF2 content exhibiting good thermal stability against devitrification. Luminescence due to (1)D2 → (1)G4 transition of Pr(3+) was measured under 450 nm excitation. The (1)D2 measured lifetimes depend critically on activator concentration, but remain nearly unchanged with BaF2 content. The emission linewidth, the emission cross-section, the figure of merit (FOM) and the σem x FWHM product are relatively large, suggesting that Pr(3+)-doped gallo-germanate glasses with presence of BaF2 are promising as gain media for broadband near-infrared amplifiers.

Growth and spectroscopy of chromium doped SrXGa3O7 (X=La, Gd) crystals

Abstract Single crystals of chromium doped SrLaGa 3 O 7 and SrGdGa 3 O 7 were grown by optical zone melting in air and by the Czochralski method in an atmosphere of nitrogen containing 1% oxygen. Crystals grown in air were blue and strongly dichroic, whereas those obtained by the Czochralski method contained separate yellow, green and blue regions. The crystal structure of these compounds are such that they have only tetrahedral sites which may be occupied by chromium ions. Therefore it is probable that the colour of the crystals is associated mainly with the absorption of Cr 4+ ions and lattice defects resulting from deviation from stoichiometry. Annealing of crystals in oxygen has a small influence on the optical absorption of the blue and green regions of the crystals but the yellow regions recover the absorption bands attributed to Cr 4+ ions. No luminescence has been detected down to liquid helium temperature.