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Two single crystals of LGSO containing 1% Dy 3+ and differing in Ce 3+ concentration were grown by the Czochralski method. XRD examination revealed that a crystal with a nominal Ce 3+ concentration of 3% has the C2/c structure inherent to Lu 2 SiO 5 (LSO) whereas a crystal with a nominal Ce 3+ concentration of 1% has the P2 1 /c structure inherent to Gd 2 SiO 5 (GSO). In both crystal structure types the excitation of Ce 3+ ions is followed by an energy transfer to Dy 3+ ions and resulting visible emission consists of a broad-band Ce 3+ luminescence and of much more narrow bands of Dy 3+ luminescence. Excitation spectra imply that the efficiency of Dy 3+ excitation via Ce 3+ – Dy 3+ energy transfer is markedly higher than upon direct optical pumping into Dy 3+ excited levels. It was observed that visible emission in the two systems differs in spectral characteristics, hence in the colour of the emitted light. Examination of optical spectra recorded with a polarized light revealed important anisotropy of transition intensities of Ce 3+ ions in LGSO host with the P2 1 /c structure. [ABSTRACT FROM AUTHOR]

Single crystal of LaGaTaO (LGT) containing intentionally 0.5 % of Ho and 1 % of Yb was grown by the Czochralski method. Examination of chemical composition of the grown crystal revealed that luminescent holmium and ytterbium ions are preferably retained in the melt and their actual concentrations are 0.12 and 0.24 %, respectively. Spectroscopic investigation performed encompassed IR host absorption spectra and Raman spectra at room temperature, optical absorption and luminescence spectra of Ho and Yb at room temperature and at 5 K, and luminescence decay curves at room temperature. It was found that all spectral bands recorded show important inhomogeneous line broadening. This feature was attributed to structural disorder inherent to the crystal lattice in which pentavalent Ta ions occupy octahedral Ga(1) sites together with trivalent Ga ions. Despite small concentrations of luminescent ions, the occurrence of nonradiative interaction that feeds the I and I levels of Ho ions by transfer of an excitation from the F level of Yb ions was evidenced. Based on examination of spectroscopic parameters evaluated, it was concluded that LGT:Ho, Yb may be considered as a potential intermediate-gain laser active material able to emit infrared radiation from the I → I transition of Ho around 2 micrometres upon laser-diode pumping into Yb absorption band. [ABSTRACT FROM AUTHOR]

Abstract: Spectroscopic properties of lutetium aluminum garnet Lu3Al5O12 (LuAG) single crystal doped with 1at.% of Pr3+ were investigated. The crystal was grown by the Czochralski method. Optical absorption, emission, excitation spectra and luminescence decay curves were recorded for this system in 5–500K temperature range. Excitation spectra in VUV–UV range (150–330nm) were also measured exploiting synchrotron radiation. It has been found that among bands of luminescence related to the 3PJ, 1D2 → 3HJ, 3FJ transition of Pr3+ in the visible region the 3P0 → 3H4 one, occurring ca. 488nm, is the most prominent. Luminescence lifetimes for the 3P0,1 and 1D2 levels were estimated to be 13 and 200μs respectively (at room temperature). VUV-excited emission spectrum stretches over the whole visible region. It has been concluded that the material under study is a promising phosphor that can be efficiently pumped by broad absorption bands centered at 240 and 280nm. [Copyright &y& Elsevier]

The Czochralski growth of Dy3+-doped (Lu1−xGdx)2SiO5 solid solution single crystals with different mixtures of Lu2SiO5 and Gd2SiO5 oxides (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) is reported. It was found that the (Lu1−xGdx)2SiO5 crystals retain structural, physical, and optical properties of Lu2SiO5 even for x = 0.8. Optical investigation of Dy:(Lu1−xGdx)2SiO5 revealed that the structural disorder of the host brings about a strong inhomogeneous broadening of Dy3+ spectral bands while influencing weakly rates of its radiative and nonradiative transitions. Dielectric characteristics of solid solution crystals are presented and discussed. Finally, (Lu1−xGdx)2SiO5 solid solution crystals seem to be an attractive alternative to a Lu2SiO5 host for the design of novel phosphors, radiation converters, and lasers owing to a significantly lower melting temperature and hence easier and less expensive manufacturing. Dy3+-doped (Lu1−xGdx)2SiO5 solid solution crystals (x = 0.2, 0.4, 0.6, 0.8) were grown by the Czochralski method and examined. The studied crystals retain structural, physical, and optical properties of Dy:Lu2SiO5 even for x = 0.8. Finally, (Lu1−xGdx)2SiO5 crystals are an interesting alternative to the Lu2SiO5 host for applications due to significantly lower melting temperatures and hence easier and less expensive manufacturing. [ABSTRACT FROM AUTHOR]

Strontium metaborate (SrB 2 O 4 ) is a suitable material for use as a matrix for luminescent dopant ions. Similarity of ionic radii of strontium and divalent europium makes it an excellent host for Eu dopant. This paper reports on the Czochralski growth and spectroscopic study of SrB 2 O 4 single crystals doped with europium and co-doped with europium and potassium. Based on recorded luminescence spectra it was found that both Eu 3+ and Eu 2+ ions occur in this host. Trivalent europium ions give rise to a narrow-band long-lived red luminescence that is not affected by incorporation of potassium ions. Divalent europium ions emit a UV–blue luminescence, consisting of a large spectral band centered at ca 430 nm. In the absence of potassium ions the decay of this luminescence deviates slightly from a single exponential time dependence with a mean lifetime value of 2.0 ns. In potassium-co-doped sample a strong deviation from a single exponential decay was observed for longer stages of decay, beginning at ca 2.5 ns. This phenomenon was attributed to dissimilarity of relaxation rates of a fraction of europium ions distributed in different lattice sites that are distorted by the presence of big potassium ions. By co-doping the host with alkali ions one can influence the oxidation state of europium ions thereby enhancing the emission of trivalent europium ions. It was concluded that the material under study is a promising phosphor for visible light emission applications. [ABSTRACT FROM AUTHOR]

Abstract: Praseodymium and cerium co-doped yttrium silicate (Pr,Ce:YSO) crystal with high optical quality was grown by the Czochralski method. The segregation coefficient of Pr3+ and Ce3+ is measured to be 0.547 and 0.136, respectively. The polarized absorption bands centered at 268nm, 299nm and 356nm were assigned to 4f (2F5/2)→5d inter-configuration transitions of Ce3+, while bands centered at 220nm and 250nm were assigned to 4fn–4fn−15d transitions of Pr3+. The VUV–UV excitation spectra for monitoring Pr3+ emissions centered at 610nm (1D2→3H4) and 489nm (3P0→3H4), as well as Ce3+ emission centered at 450nm were recorded at T=8K in the range of 100nm–320nm. Polarized excitation spectra for Ce3+ emission centered at 424nm and Pr3+ emission centered at 611nm were recorded at T=300K. Polarized emission spectra were obtained upon excitation at 365nm and 456nm at T=300K. Lifetimes were estimated to be 170μs for Pr3+ (1D2), 3μs for Pr3+ (3P0) and 39ns for Ce3+ (5d1). [Copyright &y& Elsevier]

Abstract: The (Lu x Gd0.995−x Sm0.005)2SiO5 single crystals with x=0.095, 0.11, 0.15, 0.17, 0.19 0.35 and 0.5 were grown by the Czochralski method. Structural properties were investigated by X-ray diffraction measurements. Unit cell parameters and cell volume were determined by the Rietveld refinement of the collected X-ray powder spectra. The segregation features between Gd and Lu were estimated and analyzed. Vibrational properties of the solid solutions were analyzed on the basis of polarized Raman spectra acquired at 300–875K temperature range. Absorption and emission spectra of Sm3+ ion in the crystals with different composition were analyzed in the terms of dopant energy levels, oscillator strengths of transitions and spectral features of luminescence bands in the visible range. Both structural and optical investigations revealed that change of Lu3+ content in (Lu x Gd0.995−x Sm0.005)2SiO5 solid solution crystals induces the phase transition from C2/c (Lu2SiO5) to P21/c (Gd2SiO5) structure. It was found that the break of LSO to GSO-type structure occurs at 0.15

Tm-doped (Sc 0.5 Y 0.5 ) 2 SiO 5 (SYSO) crystals were grown by Czochralski method. The UV-VIR-NIR absorption spectra and the near-infrared emission spectra were measured and analysed by the Judd-Ofelt approach. Temperature influence on both absorption and emission spectra has been determined from the data recorded at room temperature and 10 K. It has been found that the structural disorder resulting from dissimilar ionic radii of Sc 3+ and Y 3+ in the solid solution (Sc 0.5 Y 0.5 ) 2 SiO 5 crystal brings about a strong inhomogeneous broadening of Tm 3+ ions spectra. However, it affects the excited state relaxation dynamics inherent to thulium-doped Y 2 SiO 5 and Sc 2 SiO 5 hosts weakly. [ABSTRACT FROM AUTHOR]

Single crystal of Gd 3 Ga 3 Al 2 O 12 (GGAG) doped with 1 at.% Sm 3+ was fabricated by the Czochralski method. Optical absorption and emission spectra as well as luminescence decay curves for this crystal was recorded at different temperatures ranging from 5 K to 300 K. The energies of the crystal field sublevels of selected multiplets were determined based on optical spectra recorded at T = 5 K. It has been found that widths of emission spectral lines related to transitions between individual crystal field levels of multiplets are stable up to 100 K, then new Stark component of higher the 4 G 5/2 multiplets starts to appear in the spectrum. The spectral widths (FWHM) are in the range 7–30 cm −1 what is caused with solid solution composition of the crystal. Five local positions of the Sm 3+ have been found in this material. Judd-Ofelt calculation of branching ratios has been done. The color of luminescence is orange-red with CIE coordinates as x = 0.606 and y = 0.393 and the total efficiency 45%. [ABSTRACT FROM AUTHOR]

Mixed garnet crystals with nominal stoichiometry Gd 3 Al 2.5 Ga 2.5 O 12 undoped, single doped with Sm 3+ , Ho 3+ , Er 3+ and Yb 3+ and co-doped with Ho 3+ + Yb 3+ and Er 3+ + Yb 3+ were grown by the Czochralski method. Optical spectra and thermal conductivity of obtained single crystal samples were measured and analyzed. Recorded optical absorption spectra revealed that the intensity and spectral characteristics of color centre absorption in the UV region, close to the UV absorption edge of the host, are affected by the type of incorporated rare earth ions. On the other hand, spectral characteristics of stable color centers induced by an intense UV irradiation of crystals depend weakly on the rare earth admixture. Low temperature optical spectra provided the evidence that Sm 3+ ions and Er 3+ ions occupy at least two different types of sites in this host but Yb 3+ ions seem to be located preferentially in identical sites. Thermal conductivity of the crystals at 300 K, weakly affected by incorporated rare earth ions, is comparable to that reported for ordered gallium gadolinium garnet crystals. At cryogenic temperatures, i.e. below ca 80 K, thermal conductivities of the crystals containing rare earth ions are markedly smaller than that of undoped one, however. [ABSTRACT FROM AUTHOR]

Abstract: Good optical quality U3+-doped PbCl2 single crystals of the composition Pb0.99U0.01Cl2 have been obtained by the Bridgman–Stockbarger method. Luminescence spectra of the crystals were recorded in a wide spectral range at room and liquid nitrogen temperatures, and are discussed. Strong infrared emission was observed under 514nm laser pumping to the 5f26d1 bands. The lifetimes of the emitting levels in the visible and near infrared region are given. [Copyright &y& Elsevier]

Abstract: Good quality U3+ doped LaBr3 single crystals with a 0.1mol% U3+ nominal concentration have been obtained by the Bridgman–Stockbarger method. Luminescence spectra of the crystals were recorded in a wide spectral range at room temperature. Excitation in the 5f26d1 spectral region produced a strong red and near infrared emission. [Copyright &y& Elsevier]