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The thermal stability of oxyfluorotellurite glass systems, (65-x)TeO2 -20ZnF2 -12PbO-3Nb2O5 - xPr2O3 , doped with praseodymium was examined. The different concentrations of praseodymium oxide (x = 0.5 and 2 mol%) were applied to verify the thermal, optical and luminescence properties of the materials under study. The relatively high values of the Dietzel (∆T) and Saad–Poulain (S or H′ ) thermal stability factors determined using a differential thermal analysis (DTA) indicate the good thermal stability of the glass matrix, which gradually improves with the content of the active dopant. The temperature dependence of optical spectra in the temperature range 300–675 K for the VIS–NIR region was investigated. The involved Pr3+ optical transition intensities and relaxation dynamic of the praseodymium luminescent level were determined. The ultrashort femtosecond pulses were utilized to examine a dynamic relaxation of the praseodymium luminescent levels. Although the measured emission of the Pr3+ active ions in the studied glass encompasses the quite broad spectral region, the observed luminescence may only be attributed to 3PJ excited states. As a result, the observed decrease in the experimental lifetime for the 3P0 level along with the increasing activator content was identified as an intensification of the Pr–Pr interplay and the associated self-quenching process. The maximum relative sensitivities (Sr) estimated over a relatively wide temperature range are ~0.46% K−1 (at 300 K) for FIR (I530/I497) and 0.20% K−1 (at 600 K) for FIR (I630/I497), which seems to confirm the possibility of using investigated glasses in optical temperature sensors. [ABSTRACT FROM AUTHOR]

Crystals of Gd3Al2.5Ga2.5O12:Er3+, (Lu0.3Gd0.7)2SiO5:Er3+ and LiNbO3:Er3+ compounds differing in origin and the nature of their inherent structural disorder were crystalized. Optical absorption and luminescence spectra for transitions between the 4I15/2 and the 4I13/2 multiplets of Er3+ ions for the crystal samples were recorded versus temperatures in the region of 80–300 K. Gathered data were analyzed thoroughly providing the in-depth knowledge of the effects of temperature on intensities, wavelengths and bandwidths of Er3+ transitions. The information acquired together with the knowledge of significant structural dissimilarities of the host crystals chosen made it possible to propose an interpretation of the impact of a structural disorder in Er3+-doped crystals on their spectroscopic properties, and to determine their lasing ability at cryogenic temperatures upon resonant (in-band) optical pumping. [ABSTRACT FROM AUTHOR]

Novel ternary fluoro-germano-tellurite (GTS) glasses doped with Er3+ ions with 0.5 mol% and 1.0 mol% were fabricated by a conventional melt and quenching method and investigated using methods of optical spectroscopy. The room-temperature absorption spectrum was recorded and analyzed to determine radiative transition rates, radiative lifetimes, and branching ratios of Er3+ luminescence. Decay curves of Er3+ luminesccence were recorded and analyzed. Temperature dependences of emission spectra and absorption spectra in the region from RT (room-temperature) up to 675 K were studied in detail. The contribution of competing radiative and nonradiative processes to the relaxation of luminescent levels of Er3+ was assessed. Absolute and relative sensitivity were established utilizing the comprehensive model based on thermally coupled 2H11/2/4S3/2 excited states of erbium. The high quantum efficiency of the first erbium-excited state and value of gain coefficient indicate that GTS:Er glass system can be considered as conceivable NIR (near infrared) laser material as well. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 → 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 Eu 3+ excitation spectra measurements. Near-IR emission spectra at 1550 nm related to 4 I 13/2 → 4 I 15/2 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 4 I 13/2 (Er 3+ ) was proposed. The luminescence lifetime for the 4 I 13/2 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 5 D 0 lifetime increases with increasing phonon energy. Our investigations suggest that the values of measured 5 D 0 lifetime equal to radiative lifetimes for all heavy metal oxide glasses.