Lead silicate glasses co-doped with Yb<sup>3+</sup>/Er<sup>3+</sup> have been investigated. Up-conversion luminescence spectra of Er<sup>3+</sup> ions were registered under excitation of Yb<sup>3+</sup> ions by 980 nm diode laser line. Green and red luminescence bands correspond to the <sup>4</sup>S<sub>3/2</sub> - <sup>4</sup>I<sub>15/2</sub> and <sup>4</sup>F<sub>9/2</sub> - <sup>4</sup>I<sub>15/2</sub> transitions of Er<sup>3+</sup>, respectively. The luminescent transitions of Er<sup>3+</sup> ions have been also examined with temperature.
The intention of the authors is to show a possibility of controlled crystallization of Er/Yb co-doped oxyfluoride glass fibers provided for glass-ceramics core fiber lasers or optical amplifiers at 1550 nm. Selected glasses (the batch composition 48SiO<sub>2</sub>11Al<sub>2</sub>O<sub>3</sub>-7Na<sub>2</sub>CO<sub>3</sub>-10CaO-10PbO-12PbF<sub>2</sub>-1.5/0.6YbF<sub>3</sub>-0.5/0.2ErF<sub>3</sub>) were examined in the form of powders of diameter 45-100 μm (diameter comparable to that of standard multimode fiber core 62 μm). Powders were annealed at various temperatures and time periods in order to obtain glass-ceramics with different crystalline fraction. DTA measurements and calculations (isothermal and non-isothermal annealing) enabled to determine JMAK (JohnsonMehl-Avrami-Kissinger) equation parameters and to estimate crystal growth rate and certain features of nucleation stage. XRD/TEM/SAED/EDS/HRTEM/SEM/EDS techniques (X-ray diffraction, transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy) enabled to determine crystal structure of growing crystals (erbium and ytterbium enriched hexagonal PbF<sub>2</sub>, erbium and ytterbium enriched cubic PbF<sub>2</sub> isomorphic to the fluorite structure). Luminescence intensity at 1550 nm under 488/980 nm excitation has shown comparable values for glassceramics powder and for bulk glass what suggests a considerably higher emission yield for glass-ceramics fiber. The lifetime of erbium excited state for glass-ceramics powder (~4 ms) is also comparable to that of bulk glass and is promising from the point of view of a stimulated emission. Computed parameters of JMAK equation enable to establish heat treatment conditions for glass fibers and hence to control the level (fraction) of glass crystallization.
The tellurite-tungstate glasses containing small amounts of rare-earth ions have been studied experimentally at 77 and
293 K using spectroscopic methods. The photoluminescence (PL) studies reveal the emission of efficient green-yellow
light from Tb<sup>3+</sup> ions and red light from Eu<sup>3+</sup> ions. The Judd-Ofelt intensity parameters have been derived for Nd<sup>3+</sup> and
Er<sup>3+</sup> ions from the absorption spectra and they have used to calculate the radiative lifetimes and branching ratios. The
quantum efficiency η = 0.95 of the <sup>4</sup>F<sub>3/2</sub> level of Nd<sup>3+</sup> ion is higher than the typical value of other tellurite-based glasses.
For Er<sup>3+</sup> ions, PL originating from the <sup>4</sup>S<sub>3/2</sub>,<sup>4</sup>I<sub>11/2</sub> and
<sup>4</sup>I<sub>13/2</sub> levels has been observed and the luminescence decay of the
first two levels has been found to be governed by radiative transitions and multiphonon relaxation involving the highest
energy of Te-O vibrations.
Heavy metal oxide and oxyhalide glasses containing Er<sup>3+</sup> ions have been investigated. Near-infrared luminescence at
about 1550 nm and up-conversion spectra of Er<sup>3+</sup> ions were registered under excitation by 980 nm diode laser line.
Several luminescence bands are observed, which correspond to the <sup>4</sup>I<sub>13/2</sub> - <sup>4</sup>I<sub>15/2</sub> (1550 nm), <sup>2</sup>H<sub>11/2</sub>,<sup>4</sup>S<sub>3/2</sub> - <sup>4</sup>I<sub>15/2</sub> (550 nm),
<sup>4</sup>F<sub>9/2</sub> - <sup>4</sup>I<sub>15/2</sub> (670 nm) and <sup>4</sup>I<sub>9/2</sub> - <sup>4</sup>I<sub>15/2</sub> (800 nm) transitions of Er<sup>3+</sup>, respectively. The optical transitions of Er<sup>3+</sup> ions have
been examined as a function of glass host and PbX<sub>2</sub> (X = F, Cl, Br) content.
Lasing and fluorescence behavior of thulium doped YVO<sub>4</sub>, GdVO<sub>4</sub>, and LuVO<sub>4</sub> single crystals were investigated
under pulsed pumping with variable duty cycle up to CW. This allowed us to study properties of these crystals
in dependence on thermal load in a broad range. Following crystals were investigated: Tm:YVO<sub>4</sub> (5 at.% Tm/Y,
grown by the Czochralski technique), Tm:GdVO<sub>4</sub> (2, 4, and 6 at.% Tm/Gd, grown by the floating-zone technique),
and Tm:LuVO<sub>4</sub> (3 at.% Tm/Y, grown by the floating-zone technique). For pumping a fibre-coupled (core diameter
400 μm) laser diode operating in range from 800 up to 803nm was used (available CW power 20 W). All tested
crystals were investigated under CW and pulsed pumping (pulse length 4 ms). Under pulsed pumping (4% duty
cycle), the lasing was demonstrated with all samples. Under CW pumping only Tm:GdVO<sub>4</sub> crystal was lasing.
For Tm:YVO<sub>4</sub> and Tm:LuVO<sub>4</sub> crystals, a lasing was not reached for pumping with duty cycle higher than 60 %,
and the strong blue emission was observed. Detailed measurement of visible emission for broad range of pumping
duty cycles (from 4 up to 60%) showed the exponential increase of Tm<sup>3+</sup> integral emission intensity in bands
around 480 and 700 nm. Comparison with the results obtained for fixed duty cycle and variable crystal holder
temperature (290 - 310 K) allowed us to find a relation between the duty cycle and temperature of pumped part
of the crystal. Measurement of infrared fluorescence temporal behavior in dependence on duty cycle gives us
possibility to study a relative population of lasing level in dependence on temperature.
Characterization of diode pumped Er:YVO4 microchip laser working in an "eye-safe" spectral region is done. Two
active materials for microchip laser based on Er:YVO<sub>4</sub> and Er:YVO<sub>4</sub> + CaO crystals were investigated. The dimension
of the microchips was in both cases the same: an aperture 8.3 x 10.4 mm and thickness 2.9 mm. The concentration of
active ions Er<sup>3+</sup> was 0.5 at% in both samples and 0.6at% CaO was added to Er:YVO<sub>4</sub> + CaO crystal. The resonator
mirrors were deposited directly on the crystal faces: a rear mirror was HR for the 1.6 μm wavelength and HT for
0.97 μm pumping radiation and as the output coupler a dielectric coatings with the 0.5% transmission at 1.6 μm
wavelength was prepared. As a pumping source a fiber coupled (core diameter-200 μm) laser diode emitting radiation
at wavelength 0.976 μm was used. Laser diode was operating in pulsed regime (pulse width 3 ms, repetition rate 20 Hz,
maximum mean pumping power 1.13 W). The diode radiation was focused into the uncooled microchip sample by two
achromatic doublet lenses with the focal length of 75 mm. As the result 175 mW and 152 mW output peak powers were
obtained for the Er:YVO4
and Er:YVO<sub>4</sub> + CaO, respectively. The laser emission was observed in detail in range
1.529 μm up to 1.604 μm for Er:YVO<sub>4</sub> microchip in dependence on pumping conditions. For Er:YVO4 + CaO crystal
1.6041 μm was generated only. Up-conversion radiation for both materials in dependence on pumping was also studied.
Thulium doped vanadates Tm:YVO<sub>4</sub> (5 at.% Tm/Y, grown by the Czochralski technique), Tm:GdVO<sub>4</sub> (2 and
6 at.% Tm/Gd, grown by the floating-zone technique), and Tm:LuVO<sub>4</sub> (3 at.% Tm/Y, grown by the floating-zone
technique) were investigated as an active medium for diode pumped tunable laser operating around 1.9 μm. For
thulium laser tuning single 1.5mm thick Brewster-angled birefringent quartz plate (Lyot filter) was placed in
simple 80mm long linear quasi-hemispherical resonator. For thulium doped vanadates pumping a fibre-coupled
(core diameter 400 μm) temperature-tuned laser diode operating in range from 799 up to 810nm was used
(max available power 20 W). All tested crystals were investigated under CW and pulsed pumping. Under pulsed
pumping (4% duty-cycle, reduced heat generation) lasing and laser tuning was demonstrated with all available
samples. Lasers were tunable in following wavelength ranges: Tm:YVO<sub>4</sub> 5 at.% Tm/Y (1841 - 1927 nm),
Tm:GdVO<sub>4</sub> 2 at.% Tm/Gd (1830 - 1982 nm), 6 at.% Tm/Gd (1850 - 2010 nm), and Tm:LuVO<sub>4</sub> 3 at.% Tm/Lu
(1860 - 1940 nm). Under CW pumping only Tm:GdVO4 crystal was lasing (lasing of Tm:YVO4 and Tm:LuVO<sub>4</sub>
was not reached under elevated pumping duty factor). Using Tm:GdVO<sub>4</sub> (2 at.% Tm/Gd) the power up to 2.6W
and slope effciency ~ 30% (with respect to absorbed power at 808nm under lasing condition) was obtained at
wavelength 1.91 μm. Tunable operation with greater that 1W output and 130nm tuning range (1842 - 1972 nm)
was demonstrated for Tm:GdVO<sub>4</sub> (2 at.% Tm/Gd) pumped at 802 nm.
Structural and optical behavior of Pr-doped lead fluoroborate glass has been investigated. Incorporation of PbF<sub>2</sub> results in structural and optical changes around Pr<sup>3+</sup> ions and surrounding ligands, which were analyzed using X-ray diffraction, Raman, IR and luminescence spectroscopy. Shift of spectral lines has been observed, when lead oxide is totally substituted by lead fluoride in glass composition. Luminescence corresponding to the <sup>1</sup>D<sub>2</sub> - <sup>3</sup>H<sub>4</sub> transition of Pr<sup>3+</sup> ions has been detected. The peak luminescence wavelength is changed from 604 nm to 599 nm and linewidth decreases from 23.5 nm to 18 nm, whereas the infrared bands due to the B-O vibrations are shifted to lower frequency region.
Electron paramagnetic resonance spectra of La<sub>3</sub>Ga<sub>5.5</sub>Ta<sub>0.5</sub>O<sub>14</sub>:Ho single crystal for the presence of Yb<sup>3+</sup> magnetic nonequivalent centers are analyzed. Centers of different symmetries we found two of which being cubic symmetry sites. The existence of the cubic symmetry centers of the Yb<sup>3+</sup> ions in LGT host crystal confirm that Yb<sup>3+</sup> ions occupies eightfold coordinated La<sup>3+</sup> ions. The values of the g-factor for these centers are estimated as: <i>g</i> = 2.059 ± 0.004 (I centre) and <i>g</i> = 2.840 ± 0.015 (II centre). Some results of optical measurements are also presented. They indicate sharp but a weak Yb<sup>3+</sup> absorption centered at about 978 nm in the IR part of the absorption spectrum, and, equally weak Ho<sup>3+</sup> absorption in the UV-VIS part of the spectrum (fundamental absorption edge being equal to 250 nm). We think Ho and Yb ions compete in substituting of lattice sites in the crystal. Photoluminescence measurements have shown a very strong signal in the green (533 - 555 nm), slightly less in red (637 - 671 nm) and near-IR (735 - 769 nm) spectral ranges. Co-activation of the Yb-doped crystals with holmium ions leads to appearance of visible luminescence, which is explained by the Yb<sup>3+</sup>-Ho<sup>3+</sup> stepwise up-conversion mechanism. Additional absorption measurements performed after γ-irradiation with a dose of 10<sup>5</sup> Gy show wide band originating at 250 nm and extending up to 500 nm (probably due to recharged cation and oxygen vacancies) for both LGT pure and LGT:Yb, Ho single crystals, the lowering of the amount of Yb<sup>3+</sup> and Ho<sup>3+</sup> ions (due to Compton electrons capture) and additional absorption band centered at about 600 nm (charge compensating defects) for LGT:Yb, Ho single crystals. Thermoluminescence measurements (TL), does not reveal the presence of any traps in the TL glow curve.
Optical absorption and emission spectra of Eu<sup>3+</sup> ions in fluoroindate glasses have been investigated. From the experimental values of oscillator strengths with thermal correction, the Judd-Ofelt intensity parameters were obtained. These data are compared with Judd-Ofelt parameters also calculated from emission spectra. The spectroscopic parameters of Eu<sup>3+</sup> ions in fluoroindate glasses were determined and compared to the values of fluorozirconate glasses.
The InF3-based fluoride glasses doped with Tm<sup>3+</sup> and Tm<sup>3+</sup>-Tb<sup>3+</sup> ions were studied by x-ray diffusion, differential scanning calorimetry and optical spectroscopy. The thermal stability and luminescence quenching of Tm<sup>+3</sup> ions in InF<sub>3</sub>-glass have been investigated as a function of activator concentration. In the limit of low activator concentration, values of stability parameter and quantum efficiency of excited states are very high, suggestion their practical application of those glasses in optical devices.
Crystals of Er:YVO<SUB>4</SUB> were grown by Czochralski method. Uniformly doped and good quality crystals have been obtained. The lifetimes of the <SUP>4</SUP>S<SUB>3/2</SUB>, and the luminescence dynamics were studied as a function of temperature in the region 5-500K. The green luminescence around 550 nm has been observed in excitation by the Ti:sapphire laser into <SUP>4</SUP>I<SUB>11/2</SUB> level. The excitation spectrum recorded for <SUP>4</SUP>S<SUB>3/2</SUB> has been compared with absorption cross section spectrum and calculated ESA spectrum for <SUP>4</SUP>I<SUB>11/2</SUB>-<SUP>4</SUP>F<SUB>7/2</SUB> transition. The contribution of ESA process in upconversion phenomenon under excitation into <SUP>4</SUP>I<SUB>11/2</SUB> has been assessed. The emission cross-section and the gain coefficient for <SUP>4</SUP>I<SUB>13/2</SUB>-<SUP>4</SUP>I<SUB>15/2</SUB> transition of Er<SUP>3+</SUP> in YVO<SUB>4</SUB> have been calculated.
This paper deals with the excitation and decay of excited state of holmium in LiTaO<SUB>3</SUB> single crystals. Particular attention is paid to processes governing a population build up on the <SUP>5</SUP>S<SUB>2</SUB> and <SUP>5</SUP>I<SUB>7</SUB> metastable states whose quantum efficiencies are sufficiently high to be considered as initial levels for a laser transition. We observed for the first time, to our knowledge, an efficient conversion of the 647.1 nm light of a krypton ion laser into green luminescence in the material studied. Based upon analysis of excited state relaxation dynamics it is concluded that the mechanism involved is the excited state absorption from the long lived <SUP>5</SUP>I<SUB>7</SUB> level. Efficient single wavelength excitation is due to coincidence of transition energies of the ground state absorption and excited state absorption.
Crystals of LaGaO<SUB>3</SUB> were grown by the Czochralski method using seeds with different orientations. Crystal structure of LaGaO<SUB>3</SUB> is orthorombic at room temperature and rhomohedral above 425 K. Owing to the phase transition the crystals are twinned and the density of twins depends on the seed quality and orientation as well as on purity of starting materials. Two boules of LaGaO<SUB>3</SUB> containing 0.1 at% and 0.3 at% of Cr<SUP>3+</SUP> were pulled using seeds with <112> orientation. Absorption and emission spectra are consistent with a strong crystal field case in which the <SUP>2</SUP>E state is the lowest. At room temperature the luminescence consists of a broad vibronic band stretching from about 12700 cm<SUP>-1</SUP> to 15000 cm<SUP>-1</SUP>. At low temperature the phonon side band disappears and two sharp R<SUB>1</SUB> and R<SUB>2</SUB> lines can be located. Additional sharp line in spectra has been attributed to the transition of coupled Cr<SUP>3+</SUP> pairs.
In this work we investigate spectroscopic properties of Cr<SUP>3+</SUP> and Cr<SUP>3+</SUP> - Nd<SUP>3+</SUP> interaction in LiTaO<SUB>3</SUB> using optical absorption, luminescence and luminescence decay times at temperatures between 5 K and 300 K. Some preliminary data obtained with singly doped LiTaO<SUB>3</SUB>:Cr at low activator concentration are given in our previous work. Recorded spectra indicate that both the Cr<SUP>3+</SUP> and Nd<SUP>3+</SUP> are located in several non- equivalent sites which differ in the strength of the crystal field. Luminescence spectrum of Cr<SUP>3+</SUP> consists of a broad band whose maximum and intensity depend on temperature. Below about 50 K an additional sharp band with four distinct components appears in the spectrum. The broad band attributed to the spin allowed <SUP>4</SUP>T<SUB>2</SUB> - <SUP>4</SUP>A<SUB>2</SUB> transition of Cr<SUP>3+</SUP> ions overlaps two absorption bands of Nd<SUP>3+</SUP> ions at about 810 nm and 890 nm making the Cr<SUP>3+</SUP> - Nd<SUP>3+</SUP> energy transfer process feasible. Results of measurements are discussed and compared to those obtained with LiNbO<SUB>3</SUB>:Cr.
Overview of basic spectroscopic properties of several crystals belonging to two wide families of compounds is presented. Both the families form tetragonal crystals with layered structure and show certain structural disorder resulting from random distribution of divalent A atoms and trivalent B atoms. After presenting some details concerning the crystal growth and structural investigation, the nature of activator sites in the matrices is discussed. Then, the emission spectra as well as relaxation dynamics of Nd<SUP>3+</SUP>, Yb<SUP>3+</SUP>, and Tm<SUP>3+</SUP> are analyzed. After that, the basic spectroscopic features of chromium doped crystals are given. In conclusion, suitability of the crystals for the design of tunable lasers is discussed.
We examine crystals belonging to two wide families of compounds of general chemical formulae ABC<SUB>3</SUB>O<SUB>7</SUB> and ABCO<SUB>4</SUB> (A equals Ca, Sr, Ba; B equals Y, La-Gd; C equals Al, Ga) which appear to be promising active materials for the design of all-solid-state lasers. Inhomogeneous broadening of spectral lines influences weakly the extraction efficiency in the case of SrLaGa<SUB>3</SUB>O<SUB>7</SUB>:Nd and BaLaGa<SUB>3</SUB>O<SUB>7</SUB>:Nd but it is found to be a limiting factor controlling the performance of SrLaAlO<SUB>4</SUB>:Nd laser. Preliminary spectroscopic study indicates that chromium doped SrLaAlO<SUB>4</SUB> and SrLaGaO<SUB>4</SUB> may be promising active materials for the design of tunable infrared lasers.
We present the results of investigation of crystal growth optical and mechanical properties of optically uniaxial and piezoelectric crystals Owing to several advantages the crystals are well suited for practical application as laser active materials or high temperature piezoelectric sensors. I . I NT R 0 D U C T I 0 N During past few years a considerable progress has been made in the growing technique of single crystals of compounds with a general chemical formula ABC3O7 where A:Ba B:La Sm and C : Al Several compounds belonging to that large family were first obtained in the polycrystalline form y sintering the stoichiometric mixture of oxides at high temperature. 1 Preliminary x-ray investigation indicated that the crystals were of tetragonal symmetry space group P421m - D32d. Since all these compounds have identical structure and nearly the same unit cell parameters can expect that they will form solid solutions with a nonlimited or limited mutual solubility. In this paper we summarize the available information concernig the crystal growth and properties of two representatives of these compounds.