G. Dominiak-Dzik

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.

Dysprosium-doped YAl3(BO3)4 (YAB) crystals: an investigation of radiative and non-radiative processes

Abstract The absorption, emission spectra and lifetime of the 4F9/2 fluorescent level of Dy3+ in YAl3(BO3)4 crystal were investigated. Energy level structure was constructed from absorption and emission spectra recorded at 5 K. The measured oscillator strengths of the transitions between the J manifolds at 300 K were compared with those derived from the Judd–Ofelt theory. The radiative transition rates and radiative lifetimes were calculated. Although there are several transitions originating in the 4F9/2 level a major part of emission intensity is contained in the 4F9/2→6H13/2 transition. Measurement of selfquenching of the 4F9/2 luminescence provided a parameter characterizing an activator–activator interaction, which may be used to predict an optimal Dy3+ concentration. The narrow and polarization dependent emission lines, relatively long lifetime of the 4F9/2 metastable level (τ=520 μs) and its high quantum efficiency are advantageous for low threshold laser action in both CW and pulsed operation. The emission cross-section of a potential laser line at 570 nm connected with 4F9/2→6H13/2 transition was estimated.

Conversion of infrared radiation into red emission in YVO4:Yb,Ho

Upon continuous wave excitation around 1 μm, a YVO4 crystal codoped with ytterbium and holmium exhibits intense red emission originating in the 5F5 level and considerably weaker green emission originating in the 5S2 level of Ho3+. The ratio of the red to green emission intensities is 17:1 at 300 K. The dependence of the intensity of both emissions on the pump power is nearly the same but the mechanisms determined on the basis of short pulse excitation are found to be different. It is concluded that the green emission is excited by two consecutive energy transfers from Yb3+ to Ho3+, whereas excited state absorption is involved in the excitation of red emission.

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.

Optical spectra of a LaGaO3 crystal singly doped with chromium, vanadium and cobalt

Abstract Crystals of lanthanum orthogallate containing chromium, vanadium or cobalt were grown by the Czochralski method and their optical spectra were measured at room and 5K temperature. Recorded absorption and luminescence spectra of chromium ions which are convenient probes of number and type of available sites revealed that Cr3+ ions in LaGaO3 occupy identical sites with distorted octahedral symmetry and consistent with a strong crystal field case. Absorption spectra of vanadium doped LaGaO3 have been attributed to V4+ and V3+ ions coexistent in the matrix whereas a short lived and broad band luminescence recorded in the 12000–15000 cm−1 region has been attributed to the 2E–2T2 transition of V4+ ions. Absorption spectra of LaGaO3 doped with cobalt were found to be consistent with a mixed valency system containing Co2+ and Co3+. This activator–host combination did not show luminescence strong enough to be recorded with our detection systems.

Spectroscopic properties and exicted-state relaxation dynamics of Er3+ in LiNbO3

Nonequivalent Er3+ sites in LiNbO3 crystals have been evidenced by low-temperature optical absorption measurements. The radiative transition rates for the 4S3/2, 4F9/2, 4I9/2, 4I11/2, and 4I13/2 levels have been evaluated by the Judd-Ofelt method, and the contribution of multiphonon relaxation to the decay of excited states has been estimated. The quantum efficiency of the 4I11/2 level has been estimated to be 6% only, thus the excitation of levels lower than 4S3/2 is expected to populate efficiently the 4I13/2 level.

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.

Effect of temperature on excitation energy transfer and upconversion phenomena in Er:YVO4 single crystals

Abstract Investigation of excitation and decay of Er 3+ in YVO 4 single crystals has been carried out at temperature range from 5 to 500 K. In the limit of low Er 3+ content, the temperature dependence of the 4 S 3/2 decay is not consistent with predictions of multiphonon relaxation model. In heavily doped crystals the 4 S 3/2 decay is governed by cross relaxation process, whose rate grows steadily with increasing temperature. An efficient upconverted luminescence near 550 nm following a cw and short pulse (5 ns) excitation of the 4 I 9/2 level in the system under study has been recorded and analysed. Contribution of the excited state absorption to these phenomena has been considered.

Conversion of infrared radiation into visible emission in YVO4 crystals doped with ytterbium and holmium

Conversion of the infrared (IR) radiation at 975 nm into the visible emission in the Czochralski grown YVO4 crystals containing several different concentrations of Yb3+ and Ho3+ has been investigated. Unlike other matrices doped with ytterbium and holmium, the YVO4:Yb,Ho system exhibits intense red upconverted emission originating from the F55 level, whereas, green upconverted emission originating from the S25 level of Ho3+ is found to be unusually weak at room temperature but dominating at 4.2K. Power dependencies of the emissions are consistent with two-step excitation process but time dependencies differ and imply that the longlived I75 level of Ho3+ is involved in the second-step excitation of red emission. Intensity distribution of σ-polarized emission band associated with the F55-I85 transition with peak value of effective stimulated emission cross section amounting to 10−20cm2 combined with the possibility of tailoring of optical pumping efficiency by appropriate choice of dopant concentrations off...