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Nanocrystalline powders of Ce3+ doped Gd3Ga3Al2O12 (GGAG) with the size of tens nanometers were prepared using modified Pechini method. Low Temperature High Pressure sintering method was used for the fabrication of the translucent nanoceramics using as starting materials nanocrystalline GGAG:Ce3+ powders. For growth of GGAG:Ce single crystal the Czochralski method was utilized. XRD measurement was used in order to characterize the grain size of the GGAG:Ce3+ nanostructures. Excitation and emission and luminescence decays measurements were done to observe impact of the grain size and applied pressure on the spectroscopic properties of crystallites and ceramics. It was observed that for the smallest grains both spectra are significantly changed. The spectroscopic properties of the nanopowders were compared to the GGAG:Ce3+ ceramics made from them as well as to the single crystal. It was found that is possible to modify permanently the crystal field in the nanocrystals by applying the pressure during sintering.

Optical absorption spectra and luminescence spectra were recorded as a function of temperature between 295 K and 800 K for single crystal samples of Gd2SiO5:Dy3+, Lu2SiO5:Dy3+, LiNbO3:Dy3+, and Gd3Ga3Al2O12:Dy3+ fabricated by the Czochralski method and of YAl3(BO3)4:Dy3+ fabricated by the top-seeded high temperature solution method. A thermally induced change of fluorescence intensity ratio (FIR) between the 4I15/2→ 6H15/2 and 4F9/2 → 6H15/2 emission bands of Dy3+ was inferred from experimental data. It was found that relative thermal sensitivities SR at 350 K are higher for YAl3(BO3)4:Dy3+ and Lu2SiO5:Dy3+than those for the remaining systems studied. Based on detailed examination of the structural peculiarities of the crystals it was ascertained that the observed difference between thermosensitive features cannot be attributed directly to the dissimilarity of structural factors consisting of the geometry and symmetry of Dy3+ sites, the number of non-equivalent Dy3+ sites, and the host anisotropy. Instead, it was found that a meaningful correlation between relative thermal sensitivity SR and rates of radiative transitions of Dy3+ inferred from the Judd–Ofelt treatment exists. It was concluded that generalization based on the Judd–Ofelt parameters and luminescence branching ratio analysis may be useful during a preliminary assessment of thermosensitive properties of new phosphor materials.

This paper deals with broadband near-infrared luminescence properties of lead germanate glass triply doped with Yb3+/Er3+/Tm3+. Samples were excited at 800 nm and 975 nm. Their emission intensities and lifetimes depend significantly on Er3+ and Tm3+ concentrations. For samples excited at 800 nm, broadband emissions corresponding to the overlapped 3H4 → 3F4 (Tm3+) and 4I13/2 → 4I15/2 (Er3+) transitions centered at 1.45 µm and 1.5 µm was identified. Measurements of decay curves confirm reduction of 3H4 (Tm3+), 2F5/2 (Yb3+) and 4I13/2 (Er3+) luminescence lifetimes and the presence of energy-transfer processes. The maximal spectral bandwidth equal to 269 nm for the 3F4 → 3H6 transition of Tm3+ suggests that our glass co-doped with Yb3+/Er3+/Tm3+ is a good candidate for broadband near-infrared emission. The energy transfer from 4I13/2 (Er3+) to 3F4 (Tm3+) and cross-relaxation processes are responsible for the enhancement of broadband luminescence near 1.8 µm attributed to the 3F4 → 3H6 transition of thulium ions in lead germanate glass under excitation of Yb3+ ions at 975 nm.

Two neodymium(III) six-coordinate complexes NdCl3(3-Br-4-CH3OC7H7NO)3 (Nd1) and Nd(C7H9NO)5(C4H8O2)(ClO4)3 (Nd2) have been synthesized and characterized. The FT-IR and FT-Raman data were acquired, and a complete vibrational assignment of the fundamental modes of the compounds was carried out. The frequencies calculated for the both ligands and scaled using the B3LYP approach with the 6-311G(2d,2p) basis set correspond very well to the experimental values. The XRD results, IR and Raman spectra were discussed in terms of a possible structure and composition of the studied compounds. The optical absorption and emission spectra were investigated at room temperature. The emission decay is mono exponential indicating that the energy transfer from the ligand occurs straight to the 4F3/2 level. The lifetime of this level is about 2.5 μs? A possibility of the energy transfer between the ligands under study and neodymium ions was considered. The calculations of the spin Hamiltonian parameters and EPR data simulation were performed using the electron paramagnetic resonance and nuclear magnetic resonance (EPR-NMR) program.

Terbium ions in Gd3Ga3Al2O12 (GGAG) single crystal exhibit strong luminescence originated in the 5D3 and 5D4 multiplets. The decay time of the 5D3 state is 1072 μs and 724 μs at 5 K and 300 K, respectively. The time dependence of luminescence originated from the 5D4 multiplet is consistent with single exponential decay, with lifetime values 3579 μs at low temperature and 2902 μs at 300 K. The non-exponential decay curves have been fitted in the frame of Inokuti-Hirayama model, indicating that the dipole-dipole interaction plays an important role in the fluorescence quenching of the 5D3 level. The calculated R0 parameter values are equal to 11.56 A and 12.86 A for 5 and K 300 K, respectively. The positions of multiplets up to 40000 cm−1 are determined employing the f-shell empirical programs. CIE 1931 coordinates are x = 0.298 , y = 0.664 (green) at 5 K and x = 0.360, y = 0.538 (yellowish green) at 300 K.

The thermal and optical properties of oxyfluorotellurite (65-x)TeO2-20ZnF2-12PbO-3Nb2O5-xSm2O3 (x = 0.5, 2 and 5) glass systems were investigated. Glass thermal stability were monitored by differential thermal analysis (DTA) and adequate thermal stability criteria ΔT, H’ and S were determined. It was shown that the thermal stability of the investigated materials increases with the increasing of samarium ions content. The absorption and emission spectra of Sm3+ ions in oxyfluorotellurite glass were recorded in the wide spectral range from UV to NIR. Based on the Judd-Ofelt (J–O) procedure oscillator strengths, phenomenological Judd-Ofelt intensity parameters Ω2,4,6, radiative transition probabilities, branching ratios and radiative lifetimes of luminescent levels were determined. The luminescence decay curves of the 4G5/2 (Sm3+) excited state were recorded for three different concentrations of Sm3+ and corresponding experimental lifetimes were determined. Photoluminescence emission spectra were measured in the temperature range from 300 K up to 725 K to evaluate the materials under study as luminescent temperature sensor.

In this work, spectroscopic properties of europium and erbium ions in heavy metal oxide glasses have been studied. The phonon energy of the glass host was determined based on Eu3+ excitation spectra measurements. Near-IR emission spectra at 1550 nm related to 4I13/2 &rarr, 4I15/2 transition of erbium in heavy metal glasses were examined with special regards to luminescence bandwidth and measured lifetime. In particular, correlation between phonon energy and the measured lifetime 4I13/2 (Er3+) was proposed. The luminescence lifetime for the 4I13/2 upper laser state of erbium decreases with increasing phonon energy in glass matrices. Completely different results were obtained glass samples with europium ions, where the 5D0 lifetime increases with increasing phonon energy. Our investigations suggest that the values of measured 5D0 lifetime equal to radiative lifetimes for all heavy metal oxide glasses.

Crystals of LiNbO3 single-doped with Sm3+, Tb3+, or Dy3+ and crystal of LiTaO3 single-doped with Tb3+ were grown by the Czochralski method. Luminescence spectra and decay curves for LiNbO3 samples containing Sm3+ or Dy3+ ions were recorded at different temperatures between 295 and 775 K, whereas those for samples containing Tb3+ ions were recorded at different temperatures between 10 and 300 K. Optical absorption spectra at different temperatures were recorded within the UV-blue region relevant to optical pumping of the samples. It was found that the effect of temperature on experimental luminescence lifetimes consists of the initial temperature-independent stage followed by a steep decrease with the onset at about 700, 600, and 150 K for Sm3+, Dy3+, and Tb3+ ions, respectively. Additionally, comparison of temperature impact on luminescence properties of LiNbO3:Tb3+ and LiTaO3:Tb3+ crystals has been adequately described. Experimental results were interpreted in terms of temperature-dependent charge transfer (CT) transitions within the modified Temperature—Dependent Charge Transfer phenomenological model (TDCT). Disparity of the onset temperatures and their sequence were explained based on the location of familiar zigzag curves connecting the ground state levels of rare earth ions with respect to the band-gap of the host. It was concluded also that LiNbO3:Sm3+ is suitable as an optical sensor within the 500–750 K temperature region whereas LiNbO3:Dy3+ offers the highest sensitivity at lower temperatures between 300 and 400 K.

In this work, spectroscopic properties of (Lu0.25Gd0.75)2(1-x)Tm2xSiO5 (x = 0.04 and 0.005) single crystals were investigated. The material was found to be biaxial, exhibiting strong optical anisotropy, as clearly demonstrated in polarized absorption and emission spectra. Data from room temperature polarized absorption spectra were used in calculations within the phenomenological Judd-Ofelt model. The intensity parameters Ωt were established at Ω2 = 3.24 (±0.58), Ω4 = 2.96 (±0.24) and Ω6 = 0.86 (±0.14) [10−20 cm2]. The values of fluorescence lifetimes of the 1D2 and 1G4 levels were measured and subsequently compared with those calculated using the Judd-Ofelt theory. The strong absorption bands located at wavelengths around 355, 460 and 790 nm, related to the 3H6 → 1D2, 1G4, 3H4 transitions, were found suitable for optical pumping of the investigated material. The characteristics of emission spectra recorded in the blue (ca. 455 nm) and IR (ca. 1750 nm) regions indicate that further investigations of stimulated emission within those wavelength ranges are well justified and can be considered promising.

Journal of alloys and compounds 814, 152304 - (2020). doi:10.1016/j.jallcom.2019.152304, Optical, structural and morphological properties of Tm3+/Yb3+ co-doped NaYF4-based nano-glass-ceramic and a precursor glass have been investigated. The controlled heat-treatment of multicomponent oxyfluoride glass at 640 °C for 2 h was used to obtain crystalline precipitations. The differences in optical characteristics have been discussed analysing spectra recorded within wide VUV–VIS–NIR spectral range and considering relaxation dynamic of involved excited states. Optical spectra and luminescence decay curves were measured as a function of temperature in the range of 295–725 K. Based on up-converted emission spectra excited at 975 nm, temperature sensing properties of glass-ceramic were verified. The fluorescence intensity ratio between the up-converted emission bands located at around 795 nm (Tm3+:3H4–3H6) and 695 nm (Tm3+:3F3,2–3H6) was studied. The maximum relative temperature sensitivity was determined to be 0.35% K−1 at 445 K., Published by ScienceDirect, Amsterdam [u.a.]

The CsCaI3 single crystals doped with Tm2+ were grown by Bridgman technique. Divalent thulium luminescence related to the 4f13-4f13 intra-configurational and 4f125d1-4f13 inter-configurational transitions were analyzed as a function of temperature. Excited state excitation spectroscopy has been applied within a wide spectral range to examine peculiarities of transitions between different 4f125d1 excited states of Tm2+. This two-color excitation experiment was useful to assess d-d photon-absorption processes that are relevant to observed up-conversion phenomena attributed to effective anti-Stokes green luminescence around 550 nm. Furthermore, activation energy of 4f125d1 → 4f13 luminescence quenching was estimated and high value of 2F5/2 → 2F7/2 emission cross-section was determined in CsCaI3:Tm2+. Our spectroscopic study was performed to complement and verify the previous investigation in this field.

The energy levels of Er3+ ions have been determined in lithium yttrium borate (Li6Y(BO3)3) single crystals in a wide spectral range between 6000 and 40000 cm−1 together with an analysis of the ground state, using optical and EPR spectroscopy. The crystal field splittings of the 4I15/2 ground state and those of nearly all excited states up to the 4D7/2 manifold have been obtained at low temperature from luminescence (T = 5 K) and absorption (T = 9 K) measurements, respectively. The numbers of experimentally observed Stark sublevels agree well with those expected theoretically for Er3+ ions occupying a single low symmetry (C1) site. A full set of g- and 167Er hyperfine tensor parameters are presented for the ground state characterized by EPR; the measured Orbach-type spin-relaxation rates viz. the involved activation energies correspond to the optically derived lowest excited sublevels.

Influence of temperature on spectroscopic and thermal properties of Tm 3+ and Er 3+ -doped GdVO 4 and LuVO 4 crystals was examined. Polarized absorption and emission spectra as well as excited state luminescence lifetimes have been measured and analyzed especially at cryogenic temperatures in the 1.5–1.6 μm and 1.8–1.9 μm spectral ranges to assess laser qualities of these materials. The emission cross sections for 4 I 132 → 4 I 15/2 (Er) and 3 F 4 → 3 H 6 (Tm) transitions at T = 77 K were determined and confronted to the results obtained at room temperature. Effective emission cross sections estimated for aforementioned erbium and thulium transitions indicate that effective laser operation at cryogenic temperatures can be achieved in the gadolinium and lutetium vanadate crystals. Efficiency of laser material depends on its ability to heat distribution upon high-power energy pumping process. Accordingly, it has been found that the anisotropy of thermal conductivity for the undoped crystals is weakly influenced by the temperature albeit conductivity values for the GdVO 4 are higher than those for LuVO 4 at all temperatures. Incorporation of erbium or thulium ions results in a decrease of thermal conductivity in the two vanadate crystals and an anomalous temperature dependence of thermal conductivity in the LuVO 4 was observed. Anisotropy of temperature dependence of thermal conductivity was found for the LuVO 4 :3.2 at%Tm 3+ crystal. In this case the thermal conductivity along c-axis is inferior to that along a-axis of the crystal.

Oxyfluoride glasses doped with erbium and ytterbium have been fabricated at T=1460°C. To prepare glass-ceramic systems, the precursor glasses were annealed at temperature 750°C for 2h. The ordered fluoride-like crystalline phases were recognized applying XRD, SAED and EDS methods. The spectroscopic properties of the glass-ceramic samples were significantly different as compared to those observed in the precursor glass. Particularly, the emission spectra of glass-ceramics are evidence that some of Er3+ and Yb3+ ions reside into the ordered environment. Up-conversion phenomena attributed to visible anti-stokes emission of Er3+ has been observed under excitation of Yb3+ ions by a 980nm diode laser. Especially, the substantial enhancement of red up-converted luminescence was observed in the glass-ceramic system. Dissimilar spectral characteristic and relation of both aforementioned emissions examined in glass and glass-ceramic samples point at different contributions of processes relevant to up-conversion phenomena. The detailed analysis of the crucial Er3+ and Yb3+ excited states relaxation dynamics and their spectroscopic qualities has been performed to determine the mechanisms which lead to conversion of the infrared excitation into visible emission. Keywords: Oxyfluoride glasses, Glass-ceramics, Up-conversion phenomena

Spectroscopic features and laser performance of a novel thulium-doped scandium yttrium silicate crystal Tm 3+ :ScYSiO 5 (Tm:SYSO) are presented. The experimental lifetime of luminescence related to the 3 F 4 – 3 H 6 laser transition of Tm 3+ amounts to 1.1 ms, which is smaller by a factor of three than the calculated radiative lifetime value due to the contribution of nonradiative relaxation. As a consequence of the internal disordered structure of the SYSO host crystal, the luminescence bands of 3 F 4 – 3 H 6 and 3 H 4 - 3 H 6 show significant inhomogeneous spectral broadening as compared with that of SSO. The laser performances were evaluated in an end-pumped cavity using a CW semiconductor laser as a pump source. In a free run regime, the Tm:SYSO laser delivered a maximum output power of 580 mW at 2022 nm, corresponding to a slope efficiency of 17.4%. With a birefringent quartz plate inserted into laser cavity, the laser output wavelength was continuously tuned from 1950 nm to 2057 nm and dual wavelength operations at 2011 nm and 2020 nm, 1987 nm and 2045 nm, 2022 nm and 2044 nm were observed.

The paper shows some results related to thermal and optical properties of Eu3+ -doped (65-x)TeO2-20ZnF2-12PbO-3Nb2O5-xEu2O3 glass systems. Concentration of the Eu2O3 was different (x = 0.5, 2 and 5 mol%) so it could determine the influence of active admixture on relevant properties of oxyfluorotellurite glass. Thermal stability and crystalline phases formed by the glass matrix were examined by differential thermal analysis (DTA). The characteristic temperatures (glass transition temperature and oxide glass crystallization temperature) have been determined. Optical absorption and emission spectra of Eu3+ ions in oxyfluorotellurite glasses have been investigated at room temperature in the ultraviolet (UV), visible (VIS) and near-infrared (NIR) region. Oscillator strengths, phenomenological Judd-Ofelt intensity parameters Ω2,4,6, radiative transition probabilities, branching ratios and radiative lifetimes of luminescent levels have been also estimated. Lifetimes and the luminescence dynamics were studied as a function of the Eu2O3 concentration.

Polycrystalline samples of SrB4O7:1% Tm2+ were prepared in air by a solid state reaction method. High resolution spectra and decay curves for infrared luminescence related to the intraconfigurational 2F5/2 → 2F7/2 transition and for visible luminescence related to the interconfigurational transition between the lowest energy state of the 4f125d configuration and the ground 2F7/2 state of the 4f13 configuration of Tm2+ were recorded as a function of temperature between 5 and 350 K. Energies of crystal field levels of the 2F5/2 and 2F7/2 multiplets and the 2F5/2 lifetime value were determined from low temperature measurements. With these data room temperature emission and absorption spectra were calibrated in the cross-section units. It was found that the infrared emission in SrB4O7:Tm2+ is long-lived with a lifetime value of 9.5 ms and its spectrum indicates that stimulated emission near 1.18 nm may be feasible. Examination of recorded decay curves for the visible luminescence revealed that the lifetime of the lowest energy state of the 4f125d configuration depends weakly on temperature in the region 5–280 K and then shows a steep decrease when the temperature grows from about 290 K to 350 K. The evaluated values of the thermal sensitivity parameter S for SrB4O7:Tm2+ in the region 300–330 K (27–57 °C) exceed 3.9% per K with a peak at 320 K (47 °C) equal to 6.30% per K. The S value is the highest reported thus far for luminescence thermometers operating in physiological temperatures.

Optical absorption and emission spectra of Dy3+ ions in Gd3Ga3Al2O12 single crystal were investigated at room temperature and T = 5 K in the visible (VIS) and near-infrared (NIR) region. Low-temperature spectra were utilized to determine the energy level structure of Dy3+ in the GGAG host. The detailed analysis implied that optically active ions reside mainly into well-defined sites in the crystal studied. Judd–Ofelt (JO) theory was used to calculate oscillator strengths, transitions intensity parameters Ω2,4,6, radiative transition probabilities, luminescence branching ratios and radiative lifetime of dysprosium luminescent level. Relaxation dynamic of 4F9/2 excited state was examined as a function of temperature. High quantum efficiency of dysprosium luminescence level, value of the 4F9/2 → 6H13/2 yellow emission cross-section and the quality of remaining spectroscopic parameters indicate that the Gd3Ga3Al2O12:Dy3+ optical system can be considered as promising phosphor and visible laser material.

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%.

Mixed garnet crystals with nominal stoichiometry Gd3Al2.5Ga2.5O12 undoped, single doped with Sm3+, Ho3+, Er3+ and Yb3+ and co-doped with Ho3+ + Yb3+ and Er3+ + Yb3+ 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 Sm3+ ions and Er3+ ions occupy at least two different types of sites in this host but Yb3+ 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.

The existence of a recently described monoclinic phase ( C 2/ c , Z = 8) (Beregi et al., 2012) in addition to the well-known Huntite type rhombohedral ( R 32) polytypic modification of the GdAl 3 (BO 3 ) 4 (GAB) crystal at room temperature provides a unique possibility to investigate the incorporation of rare earth dopants into slightly modified crystal lattice by spectroscopic methods. In these characteristic GAB structures the dopant ions, e.g. Tb 3+ or Eu 3+ , possess slightly different neighbor geometries and local symmetries. The Tb 3+ : 7 F 6 → 5 D 4 and Eu 3+ : 7 F 0,1,2 → 5 D 0,1,2 electronic transitions were successfully identified in the absorption spectra using polarization, concentration and temperature dependent measurements in both polytypic modifications. The positions of the investigated Tb lines are shifted by up to 10 cm −1 due to symmetry changes. In addition, some of the Eu lines show splittings of about 4–30 cm −1 as a consequence of the change of the local environment. From the room temperature absorption measurements some of the low energy crystal field levels of 7 F and 5 D states of the Eu 3+ ions were successfully determined for both modifications.

Single crystals of Gd 3 (Al,Ga) 5 O 12 single doped with Ho 3+ or Yb 3+ ions and co-doped with Ho 3+ and Yb 3+ ions were grown by the Czochralski technique and investigated employing methods of optical spectroscopy. Rates of radiative transitions, branching ratio values and radiative lifetimes for excited multiplets of incorporated Ho 3+ ions were determined based on the Judd–Ofelt treatment of optical absorption spectra recorded at room temperature. Absorption spectra and luminescence spectra recorded at 5 K made it possible to determine crystal field splitting for several low energy multiplets of Ho 3+ ions and for the 2 F 5/2 multiplet of Yb 3+ ions. Lifetimes of luminescent levels of incorporated holmium and ytterbium ions and the Yb 3+ − Ho 3+ energy transfer efficiency were determined based on analysis of recorded luminescence decay curves. Up-conversion of infrared radiation at 980 nm into yellow emission in crystals co-doped with holmium and ytterbium was observed and discussed. It was found that the structural disorder of the Gd 3 (Al,Ga) 5 O 12 host resulting from a disparity of ionic radii of Al and Ga ions induces an inhomogeneous broadening of spectral lines of incorporated luminescent ions but the crystal field splitting of their multiplets is similar to that encountered in ordered garnet hosts. Based on analysis of gathered spectroscopic data it was concluded that the Gd 3 (Al,Ga) 5 O 12 :Ho 3+ ,Yb 3+ crystals are promising materials for the design of laser-diode pumped infrared lasers operating near 2000 nm.

Good quality Bi 2 WO 6 (BWO) single crystals were grown by the flux method. Transparent, light red, plate-like with sharp triangular shape BWO-A crystals were grown using NaVO 3 –B 2 O 3 solvent. Transparent, light green, plate-like BWO-B crystals were obtained using Na 2 WO 4 solvent. X-ray diffraction and scanning electron microscopy studies showed that both types of crystals are of single Aurivillius phase with the same orthorhombic symmetry. EDS analysis revealed that BWO-A crystals are solid solutions of 0.976Bi 2 WO 6 –0.012Bi 4 V 2 O 11 composition while BWO-B ones are stoichiometric of Bi 2 WO 6 composition. X-ray photoelectron spectroscopy investigations of as grown crystals showed that Bi and W ions are only in 3+ and 6+ oxidation states, respectively. Argon sputtering causes reduction of bismuth to Bi 0 (metallic) and Bi (3−x)+ valence states. Optical spectra recorded in the region 2500–350 nm did not reveal any bands that may be attributed to impurities and/or colour centre absorption. Determined energy gaps are 2.40÷2.43 eV (BWO-A) and 2.86 eV (BWO-B).

Oxyfluorotellurite (65-x)TeO2–20ZnF2–12PbO–3Nb2O5–xTm2O3 (x = 0.5, 2 and 5) and (65-x-y)TeO2–20ZnF2–12PbO–3Nb2O5–xTm2O3–yYb2O3 (x = 0.5, y = 2 and x = 0.5, y = 5) glass systems were manufactured. Glass thermal stability was examined by means of differential thermal analysis (DTA) and some thermal stability criteria ΔT, H’ and S were determined. Absorption spectrum was utilized to prepare Judd-Ofelt (J-O) calculations and consequently oscillator strengths, intensity parameters Ω2,4,6, radiative transition probabilities, branching ratios and radiative lifetimes of luminescent levels were estimated. Emission spectra and luminescence decay curves were measured as a function of temperature in the 300–625 K range. Based on the upconversion luminescence of Tm3+ the optical temperature sensor qualities have been evaluated for Tm3+/Yb3+ co-doped sample. The fluorescence intensity ratio (FIR) between transitions 700 nm (Tm3+:3F2,3 → 3H6)/800 nm (Tm3+:3H4 → 3H6) for 975 nm excitation and 700 nm (Tm3+:3F2,3 → 3H6)/470 nm (Tm3+:1G4 → 3H6) for 803 nm excitation were determined and an adequate relative thermal sensitivity S was estimated. The significant value of relative thermal sensitivity 1.12 %K−1 was determined when NIR Yb3+ and Tm3+ emission bands were analyzed, however. Effective emission cross section was calculated for 3F4 → 3H6 potential laser transition of thulium around 1.9 μm in single-doped Tm3+ glass. Furthermore, effect of temperature on down-converted and up-converted thulium and ytterbium emission and on relaxation dynamic of involved excited states was studied in details.

The La3Ga5.5Ta0.5O14 (LGT) single crystals nominally doped with 5 at.% and 1 at.% of Er3+ were grown by the Czochralski method in an atmosphere of nitrogen containing small amount of oxygen. Examination of the grown crystals employing a coupled plasma emission spectroscopy (ICP ES) revealed that actual concentrations of Er3+ ions amount to 3.8 at.% and 0.27 at.%, respectively. Absorption and emission spectra as well as relaxation of excited states of Er3+ ions in the LGT host were investigated as a function of temperature in the 300–700 K temperature region. The main attention was focused on spectroscopic properties of the LGT:Er crystal that are relevant to a potential laser operation associated with the 4I13/2 → 4I15/2 transition of Er3+ near 1.6 μm and to up-conversion of infrared radiation into green luminescence originated in the 2H11/2, 4S3/2 levels. It was found that the increase of temperature affects weakly spectral features of inhomogeneously broadened absorption bands related to the 4I15/2 → 4I11/2 and 4I15/2 → 4I13/2 transitions. Observed decrease of the 4I11/2 lifetime is consistent with calculated dependence assuming the contribution of multiphonon relaxation process that involves emission of 5 phonons with energy of 660 cm−1. Decrease of lifetime for the 2H11/2, 4S3/2 group of levels with increasing temperature, calculated assuming thermalization effects and the contribution of multiphonon relaxation, is slightly slower than experimental dependence, however. Integrated intensity of up-converted green emission excited at 980 nm diminishes quickly with increasing temperature and becomes hardly visible already at 670 K. It is supposed that this is due to simultaneous decrease of quantum efficiencies of both the intermediate 4I11/2 level and luminescent 2H11/2, 4S3/2 group of levels.

La 3 Ga 5.5 Ta 0.5 O 14 single crystals with nominal Sm 3+ concentrations of 0.5 at.% and 3 at.% were grown by the Czochralski method from iridium crucibles. Examination of chemical composition of manufactured crystals revealed that actual Sm 3+ concentrations are 0.27 at.% and 1.96 at.%, respectively. Spectroscopic measurement encompassed acquisition of absorption spectra, luminescence spectra and luminescence decay curves at temperatures between 5 K and 300 K. Analysis of room temperature absorption spectra in the framework of the Judd–Ofelt treatment made it possible to determine radiative transition rates branching ratio values related to the 4 G 5/2 luminescence of Sm 3+ ions. Crystal field splitting of Sm 3+ multiplets involved in luminescence phenomena was inferred from absorption and emission spectra recorded at 5 K. It was found that absorption and luminescence transitions exhibit strong anisotropy and their intensities for σ-polarized spectra is higher by a factor of two roughly than those for π-polarized spectra. Observed strong inhomogeneous broadening of spectral bands was attributed to certain structural disorder of the host resulting from the substitution of octahedrally coordinated Ga 3+ ions by Ta 5+ ions. It follows from calculated and experimental values of luminescence branching ratio that about 80% of excitation energy of the 4 G 5/2 metastable level is converted to visible luminescence distributed into three bands peaking at 550 nm, 600 nm and 646 nm. It was concluded that the La 3 Ga 5.5 Ta 0.5 O 14 :Sm 3+ system is promising for application as an orange–red emitting phosphor and deserves further investigation aimed at assessing its ability to show yellow laser emission.

Micro-crystalline powders of Na 3 Ce(PO 4 ) 2 orthophosphate doped with Cr 3+ ions were synthesized and characterised by means of X-ray diffraction, IR and Raman, electron absorption, magnetic and EPR studies. The emission and excitation spectra and fluorescence decay time were recorded in the temperature range 70–293 K. The spectroscopic properties of Ce 3+ and Cr 3+ ions in the studied materials were discussed in terms of the structure and local symmetry of the optical ions. These data were compared to those obtained for NaCe(PO 3 ) 4 metaphosphate.

Spectroscopic measurements of the calcium niobate CaNb 2 O 6 single crystal doped with samarium ions were performed. Polarized absorption and emission spectra as well as luminescence decay curves of this material were recorded as a function of temperature in the 5–300 K temperature region. Analysis of low temperature spectra made it possible to determine energies of crystal field components of Sm 3+ multiplets involved in the excitation and luminescence phenomena. Number of crystal field levels derived implies that Sm 3+ ions in the CaNb 2 O 6 host are accommodated in several different sites. Radiative lifetime of the 4 G 5/2 metastable level determined based on the Judd–Ofelt analysis of room temperature absorption spectra amounts to 777 μs, a value close to that of luminescence lifetime determined from luminescence decay curve. Energy transfer between the NbO 6 group and samarium ions was observed in wide temperature range. Intense luminescence related to the 4 G 5/2 → 6 H 7/2 and 4 G 5/2 → 6 H 9/2 transitions centered at 610 nm and 660 nm, respectively, combined with strong absorption band near 404 nm that matches perfectly the pump light provided by commercial InGaN/GaN diode lasers points at a potential of CaNb 2 O 6 :Sm 3+ for the design of all-solid-state visible lasers.

Single crystals of Gd 3 Ga 5 O 12 (GGG) doped with 2 at.% and 10 at.% of Sm 3+ were fabricated by the Czochralski method. Optical absorption and emission spectra as well as luminescence decay curves for these crystals were 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 spectral lines related to transitions between individual crystal field levels of multiplets involved increase by factors of 5–7 when the sample temperature grows from 5 K to 300 K. In contrast to this the positions of spectral lines appear to be independent of temperature. Temperature dependence of the 4 G 5/2 luminescence lifetime was determined for both concentrations of samarium. Luminescence decay curves follow a single-exponential time dependence when Sm 3+ concentration amounts to 2 at.% but a non-exponential decay kinetic and efficient quenching process were observed in highly-doped sample. The Inokuti–Hirayama classical energy transfer model was utilized successfully to account for time dependence of an experimental decay curves recorded for GGG:10 at.% Sm crystal.

Lead borate glasses were prepared and then heat treated in order to obtain transparent glass-ceramics. Controlled crystallization of precursor lead borate glass at appropriate annealing temperature and time led to formation of the PbWO 4 crystallites. The observed broad blue emission band is related to the PbWO 4 crystallites. The influence of PbX 2 content (X=F, Cl, Br), PbF 2 concentration and lanthanide doping (Eu, Dy) on the excitation and emission spectra of lead borate glass-ceramics containing PbWO 4 phase was examined. The relationship between Pb–X bond and spectral line width of the blue emission can be successfully observed, when halogen X ions (X=F, Cl or Br) are also present in the distorted PbWO 4 crystallites.

Solid solution crystals (LuxGd1−x)2SiO5 single doped with Sm 3+ and Dy were grown by the Czochralski method. Segregation coe cients Lu/Gd, melting temperatures and structures of solid solution crystals were determined for 0.15 ≤ x ≤ 0.8. It was found that for x ≥ 0.17 the crystals belong to the monoclinic system within a space group C2/c and their melting temperature diminishes monotonously from 1990 ◦C to 1780 ◦C when x decreases from 0.8 to 0.15. Disparity of ionic radii of Lu and Gd induces structural disorder that brings about an inhomogeneous broadening of spectral lines in absorption and emission spectra of incorporated luminescent Sm and Dy ions. Optical properties of obtained crystals were determined based on results of measurement of absorption and emission spectra and luminescence decay curves. Spectroscopic investigation revealed that Sm doped crystals show intense emission distributed in the visible-near infrared region with the most intense band centred at 605 nm and characterized by a branching ratio of 0.43. Emission spectrum of Dy doped crystals is dominated by a band centred at 575 nm and characterized by a branching ratio of 0.58. It has been concluded that the systems under study are potential laser materials able to generate visible emission upon GaN/InGaN laser diode pumping.

Spectroscopic properties of lutetium aluminum garnet Lu3Al5O12 (LuAG) single crystal doped with 1 at.% 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 5–500 K temperature range. Excitation spectra in VUV–UV range (150–330 nm) 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. 488 nm, is the most prominent. Luminescence lifetimes for the 3P0,1 and 1D2 levels were estimated to be 13 and 200 μs 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 280 nm.

Glass-ceramics containing NaYF4 nanocrystals were prepared by heat-treatment from oxyfluoride silicate-based glass doped with Ho3+ and Yb3+ ions. The formation of crystalline fluoride phase was confirmed by X-ray diffraction and transmission electron microscopy. Absorption and emission spectra revealed that a fraction of Ho3+ and Yb3+ ions is incorporated into the NaYF4 ordered lattice influencing spectroscopic features of glass-ceramics in comparison with those of precursor glass. Green up-conversion emission (545 nm) originating in the 5S2 level in glass-ceramics and up-converted red emission (650 nm) originating in the 5F5 level in as-melted glass were observed under optical pumping into Yb3+ absorption band and analyzed. Although both emissions in both materials are achieved by two-photon excitations, the relation between green and red emission intensity in glass-ceramics and glass implies that processes relevant to up-conversion phenomena are different. Based on a careful analysis of relaxation dynamics of Ho3+ and Yb3+ excited states, the mechanisms involved in conversion of the infrared radiation into the visible emission in these materials are proposed and discussed.

Single crystals of gadolinium orthosilicate Gd2SiO5 containing 0.5 at% and 5 at% of Sm3+ were grown by the Czochralski method. Optical absorption spectra, luminescence spectra and luminescence decay curves were recorded for these systems at 10 K and at room temperature. Comparison of optical spectra recorded in polarized light revealed that the anisotropy of this optically biaxial host affects the intensity distribution within absorption and emission bands related to transitions between multiplets rather than the overall band intensity. It has been found that among four bands of luminescence related to the 4G5/2→6HJ (J=5/2–11/2) transitions of Sm3+ in the visible and near infrared region the 4G5/2 →6H7/2 one has the highest intensity with a peak emission cross section of 3.54×10−21 cm2 at 601 nm for light polarized parallel to the crystallographic axis c of the crystal. The luminescence decay curve recorded for Gd2SiO5:0.5 at% Sm3+ follows a single exponential time dependence with a lifetime 1.74 ms, in good agreement with the 4G5/2 radiative lifetime τrad=1.78 ms calculated in the framework of Judd-Ofelt theory. Considerably faster and non-exponential luminescence decay recorded for Gd2SiO5:5 at% Sm3+ sample was fitted to that predicted by the Inokuti-Hirayama theory yielding the microparameter of Sm3+–Sm3+ energy transfer Cda=1.264×10−52 cm6×s−1.

Nd-doped CaF2 crystal with high optical quality was obtained by a temperature gradient technique (TGT). Energies of the crystal field levels of Nd3+ multiplets relevant to laser operation were determined based on optical spectra recorded at T = 10 K. Room temperature absorption spectra were analyzed in the framework of the Judd–Ofelt theory to calculate radiative transition rates and luminescence branching ratios for the 4F3/2 level. The 4F3/2 radiative lifetime was calculated to be 1295 μs whereas a monotonous decrease of the 4F3/2 luminescence lifetime value from 1.45 ms to 0.9 ms was observed when the temperature increased from 10 K to 300 K. The stimulated emission cross-section of 1.48 × 10−20 cm2 at 1061 nm was determined using the Fuchtbauer–Ladenburg relation. All the results showed that Nd:CaF2 would be a promising gain media in solid-state lasers.

Selected heavy metal glasses containing Yb 3+ and Er 3+ ions have been studied. Near-infrared luminescence spectra at 1.53 μm and up-conversion spectra of Er 3+ ions were registered under excitation of Yb 3+ ions by 975 nm diode laser line. The luminescence bands correspond to 4 I 13/2 – 4 I 15/2 (NIR), 4 S 3/2 – 4 I 15/2 (green) and 4 F 9/2 – 4 I 15/2 (red) transitions of Er 3+ , respectively. The optical transitions of rare earth ions have been examined as a function of glass host. The unusual large spectral linewidth nearly close to 110 nm for 4 I 13/2 – 4 I 15/2 transition of Er 3+ ions in Yb–Er co-doped lead borate glass was obtained, whereas long-lived NIR luminescence at 1.53 μm was detected in lead germanate glass. The NIR luminescence and up-conversion phenomena strongly depend on stretching vibrations of glass host, which was confirmed by FT-IR spectroscopy.

YAG:Nd powders obtained by grinding a single crystal and synthesized by modified sol–gel and combustion methods were embedded at the stage of melting in a multicomponent borate glass to obtain luminescent glass–ceramic systems. Room temperature optical absorption spectra, luminescence spectra at room temperature and at 10 K and micro-Raman spectra were recorded to determine the location of Nd 3+ ions in composite materials. It has been concluded that their luminescence characteristics depend critically on the preparation method hence the morphology of precursor crystalline YAG:Nd powders as a consequence of dissimilar solubility of crystallites in a host glass.

Transparent single crystals of erbium-doped LaVO 4 in form of platelets having an average size 0.5×2×2 mm 3 were obtained by the flux method using Pb 2 V 2 O 7 as the solvent. Inductively coupled plasma (ICP) measurement revealed that the actual Er/La=0.3% molar ratio in the crystals is lower than Er/La=1% nominal molar ratio due to significant difference of ionic radii of La and Er. Luminescence spectra and luminescence decay curves for Er 3+ transitions in the visible and near infrared region were recorded. Unpolarized Raman spectrum of undoped LaVO 4 crystal was acquired, too. Up-converted green emission following excitation at 808 and 970 nm was observed and dependence of its intensity on incident excitation power was determined. Based on experimental data gathered the relaxation dynamics of excited states of Er 3+ was analyzed and mechanisms involved in the up-conversion phenomena were discussed.

Optical Spectroscopy of the Nd Luminescence Centres in the Sr4B14O25:Nd Crystal B.V. Padlyaka,b,∗, W. Ryba-Romanowski, R. Lisiecki, Yu.S. Oseledchik, A.L. Prosvirnin, D.P. Kudryavtcev and N.V. Svitanko Institute of Physical Optics, 23 Dragomanov Str., 79005 Lviv, Ukraine University of Zielona Gora, Institute of Physics, Szafrana 4a, 65-516 Zielona Gora, Poland Institute of Low Temperatures and Structure Research, Polish Academy of Sciences

Green and red up-conversion luminescence spectra related to 2H11/2,4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of trivalent erbium in Er3+/Yb3+ co-doped lead silicate glasses have been studied. The luminescence intensity ratio for bands due to the 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions of Er3+ was determined and temperature sensitivity parameters were calculated. The maximal temperature sensitivities for Er3+/Yb3+ co-doped glass samples depend critically on rare earth ion concentrations. Based on gathered data it was concluded that Er3+/Yb3+ co-doped lead silicate glasses are promising for optical temperature sensing.

Compositional-dependent lead borate glasses doped with transition metal and rare earth ions were studied using absorption and luminescence spectroscopy. The trivalent Cr 3+ , Eu 3+ and Dy 3+ ions were used as a spectroscopic probe in glass samples with various PbO/B 2 O 3 ratios. Spectral analysis indicates that Cr 3+ ions occupy intermediate field sites; the both sites coexist and emit from the 4 T 2 (low-field) and the 2 E (high-field) states, respectively. The R and Y / B values due to 5 D 0 – 7 F 2 / 5 D 0 – 7 F 1 and 4 F 9/2 – 6 H 15/2 / 4 F 9/2 – 6 H 13/2 luminescence intensity ratios of Eu 3+ and Dy 3+ ions, respectively, increase with increasing heavy metal (PbO) content, suggesting higher asymmetry and more covalent bonding character between rare earth and oxygen ions.

LaPO 4 single crystals lightly doped with Er 3+ , and codoped with Er 3+ and Yb 3+ have been grown by spontaneous nucleation in a lead phosphate flux. Absorption and luminescence spectra have been measured in the visible and near-IR regions and the excited state dynamics has been studied upon pulsed laser excitation. The obtained results have allowed the evaluation of the effective emission cross-sections around 1.5 μm, that have been found to be similar to important oxide laser crystals doped with Er 3+ . Efficient visible upconversion has been observed upon excitation at 980 nm in the codoped crystals. This behaviour is attributed to Yb 3+ –Er 3+ energy transfer processes.