Spectroscopic Properties Of Ho Research Articles

Optical and Spectroscopic Properties of Ho:Lu2O3 Transparent Ceramics Elaborated by Spark Plasma Sintering

In this work, transparent ceramics were manufactured from nanopowders synthesized by aqueous coprecipitation followed by Spark Plasma Sintering (SPS) to ensure rapid and full densification. The photoluminescence of Ho:Lu2O3 transparent ceramics was studied in the Visible and IR domains as a function of Ho3+ dopant level from 0.5 at.% to 10 at.%. A cross-relaxation mechanism was identified and favors the 2 μm emission. All of the obtained results indicate that the optical properties are very similar between Lu2−xHoxO3 transparent ceramics and single crystals. Thus, the SPS technique appears to be a very promising method to manufacture such ceramics, which could be used as amplifier media for high-energy solid-state lasers.

Comparison of structural and spectroscopic properties of Ho3+-doped niobate compounds

Ho3+-doped YNbO4 and Y3NbO7 phosphors were synthesised via a co-precipitation synthesis route. Structural characterisation and spectroscopic properties were performed as a function of the Ho3+ concentration. The Rietveld type-refinement confirms the stabilisation of the pure monoclinic Fergusonite YNbO4 phase at the highest temperatures, but the quadratic phase is stabilised for the lowest temperature, whereas a pure cubic fluorite Y3NbO7 phase was observed for all of the heat treatments. Raman and infrared spectroscopies were used to compare the cation-oxygen vibrational modes. Emission spectra and up-conversion processes were obtained under excitation at 445 and 975 nm respectively. For a similar Ho3+ content, the energy transfers observed show differences between the two crystalline compounds that are related to a stronger interaction between the holmium cations in the fluorite host lattice.

Crystal growth, spectral properties and Judd-Ofelt analysis of Ho:GdScO3 crystal

Ho3+-doped GdScO3 crystal was successfully grown by the edge-defined film-fed growth (EFG) method. The spectroscopic properties of Ho:GdScO3 crystal were investigated at room temperature. The peak absorption cross-sections were 0.33 × 10−20 cm2 and 1.24 × 10−20 cm2 at 1160 nm and 653 nm with full widths at half maximum of 171.7 nm and 11.5 nm. The peak emission cross-sections of 5I7→5I8 and 5I6→5I7 transitions for the crystal were 0.49 × 10−20 cm2 and 1.24 × 10−20 cm2, respectively. The fluorescence lifetimes of the 5I6 and 5I7 multiplets were measured to be 1.12 ms and 6.13 ms, respectively. The results show that Ho:GdScO3 crystal is a very promising material for 3 μm laser operation.

Spectroscopic properties of Ho3+ optical centers in CaF2 crystals at the two-micron laser transition

The spectroscopic properties and lifetimes of various Ho3+ optical centers at the two-micron 5I7→5I8 laser transition were studied in CaF2 crystals at cryogenic temperatures (15 K, 77 K) using resonant selective excitation of holmium ions. For the first time, the excitation and luminescence spectra of three different optical centers with 5I7 level lifetimes of ~11 ms, ~18 ms, and ~26 ms were identified. The 18 ms lifetime optical center was ascribed to tetragonal one, the center with 26 ms lifetime is most likely a cubic one, and the center with a lifetime of 11 ms is a clustered optical center.

Fabrication and spectral properties of Ho-doped calcium fluoride transparent ceramics

The high quality of different holmium doping concentration calcium fluoride (Ho: CaF2) transparent ceramics were fabricated by hot-pressing method, which average transmittance reached to 83% at 1200 nm. The effect of Ho3+ concentrations on structural and spectroscopic properties of Ho: CaF2 transparent ceramics were investigated. With the increase of the Ho3+ ions doping concentration, the grain size of nanopowders decreased and the grain size of ceramics decreased first and then increased. The absorption coefficient of the Ho: CaF2 increased with the increase of doping concentrations. Emission and absorption cross sections of the 5I7 energy level of Ho3+ in CaF2 transparent ceramics were investigated. A strong intensity of emission peak at 2030 nm was observed, the fluorescence lifetime at 2030 nm was also investigated which indicating that Ho:CaF2 transparent ceramic is a potential candidate for 2.0 μm laser emission materials.

Optical and spectroscopic properties of Ho3+-doped fluorophosphate glasses for visible lighting applications

Holmium (Ho3+)-doped fluorophosphate glasses (P2O5–BaF2–CaF2–TiO2–Ho2O3, PCfBfTiH) were fabricated by melt-quenching technique. The glass transition (548 °C) and crystallization (577 °C) temperatures and glass stability factor (161 °C) were obtained from DSC analysis. Judd-Ofelt (JO) intensity parameters (Ω2, Ω4 and Ω6) of PCfBfTiH15 glass were evaluated. Intense green (545 nm) emission was obtained for the 5S2 + 5F4 → 5I8 transition upon excitation of 451 nm. The stimulated emission cross-section (σem) of PCfBfTiH15 glass was found to be as high as 2.01 × 10−20 cm2. Decay curves of the 5S2 + 5F4 → 5I8 transition were analyzed by double exponential function. High lifetime of 11.29 μs for the 5S2 + 5F4 level was obtained. The CIE chromaticity coordinates for the emission spectra were professed that the green emission owing to the 5S2 + 5F4 → 5I8 transition may be useful for laser and display applications at around 545 nm.

Growth and spectroscopic properties of Ho3+ doped GdYTaO4 single crystal

A promising 2.9 µm Ho:GdYTaO4 laser crystal was grown successfully by the Czochralski method for the first time. The crystal belongs to the monoclinic space group of I2/a (No. 15) and high crystalline quality is demonstrated by X-ray rocking curves. The spectral properties of Ho:GdYTaO4 crystal at room temperature are investigated. Based on the Judd–Ofelt theory, the intensity parameters, spontaneous transition probabilities, fluorescence branching ratios, and radiative lifetimes are obtained in detail. The strongest emission peak is located at 2848 nm, and the full width at half maximum is about 15 nm. The experimental lifetimes of 5I6 and 5I7 levels are 0.31 and 8.08 ms, respectively. Moreover, the Stark levels of 5I6, 5I7, and 5I8 are identified and the splitting values are calculated to be 254.1, 226.7, and 370. 4 cm−1, respectively.

Thermal stability and spectroscopic properties of Ho3+ doped tellurite-borate glasses

Ho3+ ions doped tellurite-borate glass samples with varying compositions were prepared. The compositional dependence on phenomenological Judd-Ofelt parameters was compared in different kinds of rare earth ions doped tellurite-borate glasses. Two methods were used to obtain radiative transition probability of 5I7 level with the aim of assuring the fitting quality. The integral absorption cross-sections and line shapes corresponding to 5I8→5G6 and 5I8→5I7 transition of Ho3+ ions were investigated in tellurite-borate glasses. The obtained data indicated that the integral absorption cross-sections corresponding to 5I8→5G6 transition of Ho3+ ions mainly depended on phenomenological Judd-Ofelt parameter, Ω2, because 5I8→5G6 transition belonged to hypersensitive transitions, which led to a larger Ω2 value. The change of line shapes of absorption spectra corresponding to 5I8→5G6 and 5I8→5I7 transitions of Ho3+ ions came from the lower energy regions, which could be attributed to the changed distribution of Stark levels and thermal population.

Spectroscopic properties of Ho3+ and Al3+ co-doped silica glass for 2-μm laser materials

Two series of Ho3+ and Al3+ co-doped silica glasses containing different Al2O3/Ho2O3 mole ratios and concentrations of Ho3+ ions were successfully prepared by the sol–gel method combined with high temperature sintering. Using the fluorescence spectra and fluorescence lifetimes, it was found that the optimum Al2O3/Ho2O3 mole ratio of Ho3+ and Al3+ co-doped silica glass for realizing a 2-μm laser is 15. Ho3+ and Al3+ co-doped silica glasses with compositions of xHo2O3–15xAl2O3–(100−16x) SiO2 (in mol%, x=0.14, 0.2, 0.3, 0.4, and 0.5) were designed to investigate the concentration dependence of the 2.0-μm emission and concentration quenching of the 5I7 emission. The Judd–Ofelt intensity parameters and the stimulated emission and absorption cross-sections of 0.3Ho2O3–4.5Al2O3–95.2SiO2 were systematically studied. The analysis on the relationship between the 5I7 lifetime and the Ho3+doping concentration reveals that self-quenching for a rather large Ho3+ doping range is well described by a limited diffusion process, and that the critical concentration for self-quenching is 4.84×1020ions/cm3. The results show that Ho3+ and Al3+co-doped silica glass is an ideal candidate for realizing ~2-μm laser.

Influence of modifier oxide on Spectroscopic properties of Ho3+: V4+ co-doped Na2O–SiO2–ZrO2 glasses

• EDS technique has indicated that the glasses have amorphous nature. • From the structural studies depolymerization of network takes place with V 2 O 5 . • The ESR spectra confirm that majority of vanadyl ions are in V 4+ oxidation state. • From the optical investigations, 5 S 2 → 5 I 8 is laser transition. Na 2 O–SiO 2 –ZrO 2 glasses co-doped with variable concentrations of Ho 3+ : V 4+ have been synthesized, characterized by different techniques and finally their luminescence characteristics were investigated. The EDS spectra of the glass samples indicate all the elements are intact in the final composition of prepared glass. The infrared and Raman spectral studies are carried out and the existence of conventional structural units are analyzed. The ESR and optical absorption spectra indicated that a considerable proportion of vanadium ions do exist in V 4+ state in addition to V 5+ state. The absorption and emission spectra of Ho 3+ ions were characterized using J–O theory. The radiative transition probabilities and branching ratio were evaluated from luminescence spectra. The analysis these results indicated the highest values of radiative probabilities and branching ratios for the green emission transition viz., 5 S 2 → 5 I 8 transition among various other transitions of Ho 3+ ions. However, the presence of higher concentration of V 2 O 5 in the glass matrix seems to be a hindrance for getting the high luminescence efficiency especially in the red region.

Spectroscopic analysis of efficient laser material Ho^3+:YVO_4

The spectroscopic properties of Ho3+-doped YVO4 were studied at cryogenic temperatures in the 2 µm spectral region to clarify recent observations of efficient dual-wavelength laser operation in this material. Energy levels of the 5I7 and 5I8 manifolds were determined from low-temperature absorption and fluorescence measurements. Polarized absorption cross sections were measured, and stimulated emission cross sections were determined using the reciprocity method coupled with Fuchtbauer-Ladenburg calculations. The observed laser emission wavelengths were at 2054.2 nm and 2068.5 nm. At 80 K, radiative lifetimes for the 5I7 manifold were calculated to be 3.6 ms, and fluorescence lifetimes were measured to be 2.9 ms, indicating a quantum efficiency of ~80%. Analysis of the gain cross section at 80 K and 100 K showed that the laser output wavelength is very susceptible to minor changes in temperature.

Spectroscopic properties of Ho3+ doped CaNb2O6 crystal

Results of the growth and annealing processes of Ho3+:CaNb2O6 crystal with high oxygen defects were reported. The spectroscopic properties of Ho3+:CaNb2O6 were also analysed, and the decay curves of the bulk and powder samples in correspondence with the emission 5I7→5I8 at 2·0 μm were recorded. The effects of radiative trapping on the final results were also indicated, and the final value of the fluorescence lifetimes of 5I7→5I8 transition is calculated to be 5·19 ms. CaNb2O6 crystal was shown to be a prospective material for an infrared laser medium at 2·0 μm.

Influence of In3+ ions concentration on spectroscopic properties of Ho:LiNbO3 crystals

In:Ho:LiNbO3 crystals doped with various concentrations of In3+(0, 1 mol.%, 3 mol.%, 5 mol.%), fixed concentrations of Ho3+ (1 mol.%) were grown by Czochralski method. The X-ray powder diffraction, infrared and UV-visible absorption spectra were measured and modified. Judd-Ofelt approach was employed to study the effect of In doping on spectroscopic properties of Ho:LiNbO3 crystals. In concentrations in crystals were analyzed by an inductively coupled plasma optical emission spectrometry (ICP-OE/MS). For In (3 mol.%):Ho (1 mol.%):LiNbO3 crystal, the obtained intensity parameters were: Ω2=9.6563, Ω4=4.2195, Ω6=14.1526. The results showed that the Ω2 and Ω6 parameters increased with the increase of In3+ concentration. When the In doping concentration was up to 5 mol.%, Ω2 and Ω6 suddenly decreased. In2O3 incorporation had a strong effect on the radiative lifetime, but had less influence on fluorescence branching ratios. The effective distribution coefficient of In3+ in In:Ho:LiNbO3 crystals was less than 1 and increased with increasing concentration of In3+ in the melt.

Spectroscopic properties of Ho3+ single-doped and Tm3+/Ho3+ co-doped LiLa(MoO4)2 crystals

Spectroscopic properties of Ho3+ : LiLa(MoO4)2 and Tm3+/Ho3+ : LiLa(MoO4)2 single crystals relevant to the 2 µm laser of Ho3+ ions have been investigated. The polarized absorption spectra of the crystals were measured. The stimulated emission cross sections of the 5I7 → 5I8 transition for Ho3+ ions were estimated. The fluorescence spectra around 2 µm and upconversion fluorescence spectra in the visible region under excitation at 795 nm were measured. The fluorescence decay curves of the 3H4 and 3F4 multiplets of Tm3+ ions and the 5I7 multiplet of Ho3+ ions were recorded. The cross relaxation of 3H4 + 3H6 → 3F4 + 3F4 between Tm3+ ions and the following energy transfer between the 3F4 multiplet of Tm3+ ions and the 5I7 multiplet of Ho3+ ions in the Tm3+/Ho3+ : LiLa(MoO4)2 were analysed.

Spectroscopic studies of KGd(WO 4) 2:Ho 3+ single crystals

Single crystals of KGd(WO 4) 2 doped with Ho 3+ ions were grown by the top seeded solution growth method. Polarized room temperature absorption spectra were analyzed by means of the conventional Judd–Ofelt theory taking into account strong dependence of the host refractive index on the wavelength. In addition to the intensity parameters Ω 2, Ω 4, Ω 6, the branching ratios and radiative lifetimes were estimated for all possible transitions in the studied spectral region. The transitions predicted by the phenomenological model as potential transitions for laser applications are discussed. Emission spectra in the green, red, and near-infrared spectral regions were recorded for different excitation wavelengths. Comparison with spectroscopic properties of Ho 3+ ion in other crystals is discussed.

Spectroscopic properties of Ho3+/Yb3+ codoped lanthanum aluminum germanate glasses with efficient energy transfer

Ho 3 + / Yb 3 + codoped lanthanum aluminum germanate glasses are prepared simply by melt-quenching method. The 2 μm emission characteristic and energy transfer from Yb3+ to Ho3+ upon excitation of a conventional 980 nm laser diode is investigated and the energy transfer efficiency is as high as 83%. The spectroscopic parameters are calculated based on Judd–Ofelt (J-O) theory, the intensity parameters Ω2, Ω4, and Ω6 are 4.44, 1.92, and 1.11×10−20 cm2, respectively. The transition probabilities and branching ratios are also estimated by using the J-O parameters. Beer–Lambert and Fuchtbauer–Ladenburg theories are applied to calculate the absorption, emission, and gain cross sections of I57→I58 transition.

Local structure and its effect on the oscillator strengths and emission properties of Ho3+ in chalcohalide glasses

The formation of structural units in Ge–Ga–S glass with CsBr addition and its effect on the optical band gap and several spectroscopic properties of Ho3+ were investigated. The optical band gap of the host glasses and the oscillator strengths of Ho3+ absorption decreased sharply when the ratio of CsBr/Ga became close to unity. These property changes were associated with the formation of structural units of [GaS3/2Br]− and they have a crucial effect on the changes of the local structure around Ho3+ ions. The local structure was not sensitive to the As or Br addition but was critically dependent on the concentration of CsBr.

Inhomogeneity of Ho3+ activated SrLaGa3O7 and SrLaGaO4 crystals studied by fluorescence line narrowing technique

Spectroscopic properties of Ho3+ in SrLaGa3O7 (SLG) and SrLaGaO4 (SLO) are studied using non-resonant fluorescence line narrowing technique. Spectrally-different ions in inhomogeneous absorption line of holmium are selectively excited. The low temperature emission and fluorescence decays from the 5S2 level of Ho3+ ion after pulsed 5I8 → 5S2 excitation transition are investigated. The observed line-narrowed fluorescence is used to analyze the origin of spectral line broadening phenomenon in SLG and SLO hosts. Based on the experimental results an influence of the statistical distribution of La3+ and Sr2+ ions in crystal lattice on the spectroscopic properties of Ho3+ is discussed.

The effect of mixed alkalis on the absorption and fluorescence properties ofHo3+ ions in borate glasses

Spectroscopic properties of Ho3+ in 67B2O3·xLi2O ·(32−x)Na2O,67B2O3·xLi2O ·(32−x)K2O and67B2O3·xLi2O ·(32−x)Cs2O (wherex = 8, 12, 16,20 and 24) glasses were investigated on the basis of Judd–Ofelt theory. Various spectroscopic parameters(E1,E2,E3,ξ4f,α andβ) and Judd–Ofeltintensity parameters (Ω2, Ω4 andΩ6) are calculatedas a function of x in the three glass matrices. The obtained Judd–Ofelt intensity parameterΩ2 increases with the addition of a second alkali and also shows minima or maxima atx = 16–20 mol % in the above glasses. Using Judd–Ofelt intensity parameters(Ω2,Ω4 andΩ6), radiative transitionprobabilities (AT),radiative lifetimes (τR), branching ratios (β) and integrated absorption cross sections(Σ) have been calculated for certain excited states ofHo3+. The non-radiative transition rates of different excited states ofHo3+ arealso estimated from ‘energy gap law’. From the luminescence spectra, stimulated emission cross-sections(σp) have been obtained for the two transitions and of Ho3+. The trend of all these parameters observed as a function ofx in these glass systems have been discussed, keeping in mind the effect of mixed alkalis.

Spectroscopic properties of Ho 3+ ions doped in tellurite glass

Spectroscopic properties of Ho 3+ doped tellurite glass (1 mol.% of Ho 3+) have been studied. The absorption and fluorescence spectra have been recorded and analysed using the Judd–Offelt theory. The analysis indicates that Ho doped tellurite glasses can show lasing on the 5F 4 ( 5S 2)– 5I 8 transition (548.0 nm).