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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.

Gd3(Al,Ga)5O12:RE3+, Yb3+ single crystals (RE3+ = Tm3+, Er3+, Ho3+, Pr3+) were fabricated by the Czochralski technique. Effect of Yb3+ concentration on spectral distribution of luminescence emitted by interacting RE3+-Yb3+ ion pairs and on the dynamics of excitation energy flow in systems under study was investigated and interpreted referring to previously reported spectroscopic features of Gd3(Al,Ga)5O12:RE3+ systems. It was concluded that observed quenching of the Yb3+ emission by co-doped rare earth ions results from an interplay between phenomena of quantum cutting, down shifting and energy dissipation by multiphonon emission.

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.

Spectroscopic properties of Gd3Ga3Al2O12 (GGAG) single crystals co-doped with various configurations of (Eu + Tb); (Eu + Ce); (Tb + Ce) and (Eu+ Tb + Ce) ions have been investigated. The effect of distinct Ln3+ co-doping variations on luminescence of garnet crystals was studied using the different excitation wavelengths. The Ln3+-Ln3+ and host-Ln3+ interplays have been considered in doubly and triply doped GGAG:Ln3+. The crystals containing cerium ions are characterized by mainly broadband emission in the 450–750 nm spectral region that is adequately modified in green and red spectral range in the samples co-doped with terbium and europium, respectively. The Eu3+ luminescence in materials under study is selectively excited employing solely f-f europium transitions. Contrary to that, emission of terbium and cerium occur as result of interaction with Gd3+ and adjacent co-dopants.

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.]

Eu3+ complex with 1-(2,6-dihydroxyphenyl)ethanone in the solid state has been synthesized and characterized by elemental analysis, UV-visible, FT-IR and FT-Raman spectroscopies, powder X-ray diffraction, electron emission under femtosecond laser excitation. The stoichiometry and the formula of the studied complex have been proposed. Its physicochemical properties have been analyzed in terms of the structure and DFT calculations performed for the ligand. The luminescence and dynamics of the excited states depopulation have been studied using femtosecond laser excitation. Spectral and energetic transformation of femtosecond light impulses has been studied and possibility of the energy transfer between the ligand and the Eu3+ electron levels has been analyzed.

Oxyfluorotellurite (65-x)TeO2–20ZnF2–12PbO–3Nb2O5–xLn2O3 (Ln = Nd3+ and Yb3+, x = 0.5, 2 and 5) and (65-x-y)TeO2–20ZnF2–12PbO–3Nb2O5–xNd2O3–yYb2O3 (x = 0.5, y = 2 and x = 0.5, y = 5) glass systems were fabricated and their optical and thermal properties were investigated. Absorption and emission spectra of RE admixture ions in oxyfluorotellurite glasses were measured and examined at room temperature in the wide spectral region. Oscillator strengths, phenomenological Judd-Ofelt (J–O) intensity parameters, radiative transition probabilities, branching ratios and radiative lifetimes of luminescent levels were determined. Luminescence decay curves of the 4F3/2 (Nd3+) and 2F5/2 (Yb3+) excited states were recorded and comprehensively analyzed for the single-doped Nd3+ and Nd3+–Yb3+ co-doped samples. Relaxation dynamics of luminescent levels were studied as a function of the Nd3+ and Yb3+ concentrations. An effective non-resonant phonon assisted energy transfer from neodymium to ytterbium was observed and studied. It was found that good thermal stability combined with proper spectroscopic parameters of examined Nd, Yb-doped oxyfluorotellurite glasses imply the suitability of these materials for the design of NIR-emitting efficient optical devices. Furthermore, the ability of the Nd3+ ions in oxyfluorotellurite glass host as luminescent temperature sensor was verified. Relative intensity ratios of neodymium transitions originated in 4F7/2/4F3/2 and 4F5/2/4F3/2 thermally coupled closely-located excited states have been adequately determined and studied.

A solid state Eu3+ complex with dehydroacetic acid (DHA) has been synthesized and characterized by elemental analysis, UV–visible, FT-IR, FT-Raman, powder and single-crystal X-ray diffraction and optical spectroscopy studies. The complex has formula [Eu(DHA)2(H2O)5]NO3 with DHA = C8H7O4−, where the europium ions is in monocapped distorted square antiprism environment with coordination number nine. Its photophysical properties have been analyzed in terms of its molecular structure and DFT calculations performed for the representative crystal fragment including Eu3+ and two DHA ligands. The luminescence and dynamics of the excited states depopulation have been studied using femtosecond laser excitation. The energy transfer mechanism between the ligand and Eu3+ electronic energy levels has been proposed. The obtained results have been compared to those of Gd3+ dehydroacetic derivative.

Single crystals of Gd3Al2.5Ga2.5O12, single-doped with Pr3+ ions and double-doped with Pr3+ and Yb3+ ions, were fabricated by the Czochralski technique. Transition intensities and relaxation dynamics of Pr3+ ions were determined employing the Judd–Ofelt treatment. Crystal field splitting of excited multiplets of incorporated luminescent ions were determined on the basis of optical spectra recorded at liquid helium temperature. The Pr3+ → Yb3+ energy-transfer phenomena were determined analyzing the effect of Yb3+ concentration on luminescence spectra and decay curves of Pr3+ ions. It was concluded that the observed downconversion phenomenon involves a quantum-cutting mechanism consisting of a two-step energy transfer from Pr3+ to Yb3+. We observed a phenomenon of nonresonant conversion of femtosecond pulses of infrared light into visible Pr3+ emission that was weakly affected by the wavelength of incident light at least in the 1100–1600 nm region. It was concluded that excitation mechanisms consist of mult...

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.

Tm-doped (Sc0.5Y0.5)2SiO5 (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 Sc3+ and Y3+ in the solid solution (Sc0.5Y0.5)2SiO5 crystal brings about a strong inhomogeneous broadening of Tm3+ ions spectra. However, it affects the excited state relaxation dynamics inherent to thulium-doped Y2SiO5 and Sc2SiO5 hosts weakly.

Samarium(2+) doped single crystals of SrCl 2 , SrBr 2 and SrI 2 with a nominal samarium concentration of 0.12, 0.16 and 0.13 at%, respectively, were grown by the Bridgman method. XRD examination revealed that obtained samples are single phase and their structures are consistent with those intentional. Based on preliminary spectroscopic measurement it was ascertained that Sm 2+ ions are incorporated without traces of Sm 3+ contamination. High resolution absorption, luminescence and excitation spectra as well as luminescence decay curves were measured as a function of temperature in the 4.2–300 K region. It was found that structural peculiarities of the host crystals affect strongly spectroscopic features of incorporated Sm 2+ ions. At room temperature all systems under study show a broad-band luminescence related to the parity allowed inter-configurational 4f 5 5d 1 – 4f 6 transitions of Sm 2+ . At 5 K a broad band luminescence vanishes in SrCl 2 :Sm 2+ and a resulting luminescence spectrum shows a rich fine structure consisting of narrow lines that we attribute to magnetic dipole transitions within the 4f 6 configuration of Sm 2+ ions located in centro-symmetric sites and/or their vibrational side bands. Based on an analysis of luminescence decay curves we attribute numerous narrow lines that appear in luminescence spectra of SrBr 2 :Sm 2+ recorded below 25 K to the 5 D 0 – 7 F J ( J = 0–4) intra-configurational transitions of Sm 2+ ions located in sites with C 4 and C 1 symmetry. A long-lived luminescence related to intra-configurational transitions was not observed in SrI 2 :Sm 2+ even at 4.2 K.

Temperature-dependent up-conversion luminescence spectra of Er 3+ in lead-free germanate glass have been examined under 800 nm and 980 nm diode laser excitation. Green up-conversion luminescence spectra measured in the 500–580 nm ranges correspond to transitions originating from thermally coupled 2 H 11/2 and 4 S 3/2 levels to 4 I 15/2 ground level of Er 3+ . The relative emission band intensities of 2 H 11/2 → 4 I 15/2 and 4 S 3/2 → 4 I 15/2 transitions of Er 3+ are changed with temperature. The rate of fluorescence intensity ratio varying with temperature was calculated for glass sample excited at 800 nm and 980 nm, respectively. The maximum temperature sensitivity is nearly 20% higher for glass sample pumped at 980 nm than 800 nm.

Single crystals of Gd 3 Al 2.5 Ga 2.5 O 12 (GAGG) doped with Tm 3+ ions and co-doped with Ho 3+ and Tm 3+ ions were grown by the Czochralski technique and investigated employing methods of optical spectroscopy. The room temperature absorption spectra of GAGG:Tm 3+ were analysed in the framework of the Judd-Ofelt theory. Obtained phenomenological parameters Ω 2 = 0.62 × 10 −20 cm 2 , Ω 4 = 1.41 × 10 −20 cm 2 and Ω 6 = 0.80 × 10 −20 cm 2 were used to determine rates of radiative transitions, branching ratio values and radiative lifetimes for excited multiples of incorporated Tm 3+ ions. Effect of Tm 3+ concentration on decay curves of Tm 3+ luminescence was examined and spectroscopic parameters characterizing the donor-acceptor interaction responsible for self-quenching of the emission from the 1 D 2 , 1 G 4 and 3 H 4 multiplets were evaluated applying the Inokuti-Hirayama model. The crystal field splitting of Tm 3+ multiplets were determined based on low temperature absorption and emission spectra. The emission cross section for Tm 3+ : 3 F 4 → 3 H 6 luminescence was determined to be 0.31 × 10 −20 cm 2 at maximum and corresponding experimental lifetime amounts to 4.3 ms resulting in quantum efficiency η = 0.79. The calculated ratio of Tm-Ho to back-transfer processes (C Tm-Ho /C Ho-Tm ) is 5.18.

Up-conversion luminescence spectra of Er3+ ions in multicomponent oxyfluoride glasses GeO2 – BaO – BaF2 – Ga2O3 – Er2O3 were examined. It was found that the up-conversion luminescence spectra of Er3+ are dependent on pumping wavelengths. The spectra recorded upon the excitation at 800 nm contained an intense green up-conversion luminescence corresponding to the 2H11/2, 4S3/2 → 4I15/2 transitions and a very weak red luminescence related to the 4F9/2 - 4I15/2 transition. In spectra recorded upon 980 nm excitation the contribution of the red luminescence was markedly higher. The interaction mechanisms involved in up-conversion processes are proposed and observed dependence of intensity of up-converted luminescence on excitation power is discussed. The experimental results suggest that Er3+ singly doped lead-free oxyfluoride germanate glass is useful for up-conversion luminescence applications.

Nanocrystalline powders of Eu3+ doped Gd3Ga3Al2O12 (GGAG) were prepared using a modified Pechini method. The nanocrystals with the size from tens to hundreds of nanometers were obtained. For growth of single crystal GGAG:Eu the Czochralski method was utilized. The crystal structure, grain morphology, and optical properties of GGAG doped with different concentration of Eu3+ and calcined at different temperatures were investigated and discussed. The impact of grain size and Eu3+ concentration on the spectroscopic properties of Gd3Ga3Al2O12:Eu3+ was checked and analyzed. The spectroscopic properties of the nanopowders were compared to the Gd3Ga3Al2O12:Eu3+ single crystal. The influence of effective index of refraction was taken into account in the analysis of transition rates of metastable multiplet and it was found that grain size (surface area) of the nanocrystals has a huge impact on the luminescence decay time.

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.

Eu 3+ complex with 2-hydroxy-4-metoxy-benzophenone (HMBP) in solid state has been synthesized and characterized by elemental analysis, UV–visible, FT-IR, FT-Raman spectroscopies, powder X-ray diffraction, electron emission excited by femtosecond pulses. The stoichiometry and formula of the studied complex have been proposed. Its physicochemical properties have been analyzed in terms of structure and DFT calculations performed for the ligand. The luminescence and dynamics of the excited states depopulation were studied using femtosecond laser excitation. The spectral and energetic transformation of femtosecond light pulses have been discussed and a possibility of an energy transfer between the singlet state of the ligand and the Eu 3+ electron levels has been considered.

Erbium-doped lead silicate glass has been investigated for near-infrared emission and up-conversion applications. Near-infrared emission due to 4 I 13/2 → 4 I 15/2 transition of Er 3+ is relatively broad (70.5 nm) and long-lived (3.7 ms). Also, up-conversion luminescence spectra of Er 3+ ions in lead silicate glass have been examined as a function of temperature. The relative intensities of luminescence bands corresponding to 2 H 11/2 → 4 I 15/2 and 4 S 3/2 → 4 I 15/2 transitions of Er 3+ were determined with temperature. The fluorescence intensity ratio and temperature sensitivity were calculated. The maximum sensitivity for Er 3+ doped lead silicate glass is close to 26.4 × 10 −4 K −1 at T = 590 K.

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.

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.

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%.

Er 3+ /Yb 3+ co-doped lead germanate glasses have been examined for up-conversion luminescence temperature sensors. Up-conversion luminescence spectra corresponding to 2 H 11/2 → 4 I 15/2 and 4 S 3/2 → 4 I 15/2 transitions of Er 3+ are changed with temperature. The fluorescence intensity ratio (FIR) and temperature sensitivity were determined. The maximum sensitivity is found to be 70 × 10 −4 K −1 at T = 550 K in the temperature range of 300–600 K. It suggests that Er 3+ /Yb 3+ co-doped lead germanate glass is promising for optical temperature sensors.

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.

In a comprehensive and novel approach, a diverse set of five functional models of temperature sensing were established for erbium-doped oxyfluorotellurite glass systems using temperature dependences of emission spectra and luminescence dynamics in the range from RT to up to 675 K. Maximum relative sensitivity at 300 K was established at 1.52%K−1 for the model based on thermally coupled levels and at 1.92%K−1 at 675 K utilizing the green-to-red ratio. To confirm usefulness of the models established for the considered glasses, material and spectroscopic analyses were performed. Differential thermal analysis yielded favorable results in terms of glass thermal stability, further improving with increase of dopant concentration. Radiative transition analysis was performed, along with calculation of absorption, emission and effective emission cross sections, yielding information on the lasing performance of the material. It was found that TZPN:Er is a promising material for temperature sensing and optical amplification in the C and L telecom bands.

[Ln2(2-hydroxy-5-methyl-nicotinic acid)6(H2O)4] and Ln2(5-methyl-nicotinic acid)6(H2O)4] complexes (Ln = Gd, Tb) have been synthesized and characterized by means of powder X-ray diffraction, IR, Raman, electron UV–Vis and emission measurements. The luminescence and dynamics of the excited states depopulation have been studied using femtosecond laser excitation. The singlet and triplet states of nicotinic acid were localized using DFT quantum chemical calculations. The energy transfer mechanism between the electron levels of the ligands and Tb3+ ion have been proposed.

Single crystals of Gd3(Al,Ga)5O12 (GAGG) doped with Er3+ or Yb3+ ions and co-doped with Er3+ and Yb3+ ions were grown successfully by the Czochralski technique. Their optical properties were investigated in detail. Rates of radiative transitions, branching ratio values and radiative lifetimes for excited multiplets of incorporated Er3+ were determined based on the Judd–Ofelt treatment of optical absorption spectra recorded at room temperature. Obtained parameters Ωt (t=2, 4, and 6) are 1.47×10−20 cm2, 1.38×10−20 cm2, and 1.19×10−20 cm2 respectively. Low energy crystal levels of Er3+ in GAGG were determined employing absorption and luminescence spectra recorded at 5 K. Consequently, the energy diagram constructed was used to substantial discussion of obtained experimental data. Up-conversion of infrared radiation at 980 nm into visible emission in crystals co-doped with erbium and ytterbium was observed and discussed. It was concluded that gathered spectroscopic data point at the potential of the GAGG:Yb3+, Er3+ system for application as a laser active material operating around 1500 nm within the 4I13/2→4I15/2 transition of Er3+.