Holmium Ions Research Articles

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.

Er3+/Ho3+ codoped nanogarnet as an optical FIR based thermometer for a wide range of high and low temperatures

In this work, a new strategy to increase the temperature working range of rare-earth based optical thermometers is demonstrated. Nanocrystalline yttrium gallium nanogarnets codoped with 0.1% Er3+ and 0.1% Ho3+ were synthesized. The codoped samples combine the high performance of erbium ions at high temperatures and that of holmium ions at low temperature, providing an overall relatively high sensor performance in a temperature range from 30 to 540 K, broader than that achievable by single Er3+ or Ho3+ doped nanogarnets. Measurements were carried out using 406 and 473 nm commercial diode lasers to excite the erbium and holmium ions, respectively. The emission spectra were analyzed as a function of temperature, using the fluorescence intensity ratio technique for each ion. Relative sensitivity and limit of detection were obtained in order to compare the efficiency of the sensor with optical thermometers reported up to date, capable of working in a similar range from cryogenic to high temperatures. The sensor presents a maximum relative sensitivity of about 1.3% K−1 at 200 K when exciting the erbium ions and around 0.4% K−1 at 200 K for the holmium ions. The limit of detection is under 0.5 K for most of the range from 30 K to 540 K using this combination of ions.

Realization and simulation of high-power holmium doped fiber lasers for long-range transmission

We report on our realization of a high-power holmium doped fiber laser, together with the validation of our numerical simulation of the laser. We first present the measurements of the physical parameters that are mandatory to model accurately the laser-holmium interactions in our silica fiber. We then describe the realization of the clad-pumped laser, based on a triple-clad large mode area holmium (Ho) doped silica fiber. The output signal power is 90 W at 2120 nm, with an efficiency of about 50% with respect to the coupled pump power. This efficiency corresponds to the state of the art for clad-pumped Ho-doped fiber lasers in the 100 W power class. By comparing the experimental results to our simulation, we demonstrate its validity and use it to show that the efficiency is limited, for our fiber, by the non-saturable absorption caused by pair-induced quenching between adjacent holmium ions.

Impact of Ho and Ce Ions Substitution on Structural, Electrical, and Dielectric Properties of Ni-Zn Ferrites

In the present study, influence of holmium (Ho) and cerium (Ce) ions on the electromagnetic properties of Ni0.67Zn0.33Fe1.9Ho0.1-xCexO4 ferrites (x = 0, 0.025, 0.05, 0.075, 0.1) synthesized by the self-ignited sol-gel method was studied. The XRD experiment was performed to determine the substitutional effects on structural parameters. FTIR spectroscopy and I-V measurements were carried out to analyze the spectral and electrical behavior of substituted samples. X-ray diffraction patterns revealed the FCC structure of the prepared samples The value of average crystallite size was noticed between 25.89-39.51 nm, while lattice constant was found in the range 8.37-8.41 Å. Both the low and the high frequency absorption bands were confirmed by FTIR technique. Tetrahedral band was noted in the range 463-495 cm-1 while octahedral band was observed in range 558-560 cm-1. The dc resistivity was observed to decrease with increase in temperature which indicates the semi-conductor like behavior of the prepared samples. Dielectric study showed that both the dielectric constant and the tangent loss factor were decreased with rise in the applied field frequency.

Inorganic fluorescent marker materials for identification of post-consumer plastic packaging

Current plastic packaging waste management practices in Europe, but also in other countries require improvement due to legal and societal requirements. To meet high recycling rates, significant changes among others in post-consumer packaging waste sorting become necessary. This waste stream is dominated by plastic packaging. Inorganic fluorescent tracer materials (oxide crystals doped with ytterbium Yb3+ sensitizer ions and either erbium (Er3+), holmium (Ho3+) or thulium (Tm3+) activator ions) enable a sorting criterion which is independent of the properties of the packaging materials. The authors propose to use up-conversion fluorescence as a unique mean for polymer marking and product identification. To this end, PE-HD film samples, with 10, 100 and 1000 ppm of marker concentration in different polymer matrix colours (semi-transparent, yellow, green, and black) were irradiated with 980 nm diode laser radiation, with an excitation intensity up to 10 W/cm2. The performance of three different marker types with their maximum emission in green, red, and NIR was measured and assessed both with and without polymer matrix. Moreover, PE-HD sample bottles with tracers were tested, and a tracer regime for specific code generation for improved polymer identification is proposed.

Сrystal structure, valence state of ions and magnetic properties of HoFeO3 and HoFe0.8Sc0.2O3 nanoparticles from X-ray diffraction, X-ray photoelectron, and Mössbauer spectroscopy data

Abstract The HoFeO3 and HoFe0.8Sc0.2O3 nanoparticle samples were prepared by the solution combustion method using a mixture of fuels as carbamide and glucose. Their structural, electronic and magnetic properties are studied. The XRD study confirmed that the samples were single-phased and had Pbnm orthorhombic structure. The partial substitutions of Fe3+ ions by the Sc3+ ions with larger ionic radii resulted in the growth of lattice parameters. The surface morphology of the samples was examined by the scanning electron microscopy. The XPS data confirmed that both iron and scandium in the samples are trivalent. However, holmium was found to be trivalent only in the sample with a nominal composition HoFeO3. The data processing for the sample with a nominal composition of HoFe0.8Sc0.2O3 indicated that holmium ions were in Ho2+ and Ho3+ states with the ratio of 0.45/0.55. The Mossbauer study showed that iron ions in both samples were in Fe3+ state. About 10% of Fe3+ ions in HoFe0.8Sc0.2O3 were found to be in local environment with the coordination number 4. Collecting Mossbauer spectra in the temperature range of 14–723K allowed estimating magnetic phase transition temperatures (TM) for HoFeO3 and HoFe0.8Sc0.2O3 nanoparticle samples. TM values are 640K for HoFeO3 and 385K for HoFe0.8Sc0.2O3.

Refractive index of fluoride crystals doped with rare earth ions with low concentration

Refractive indices of SrF2 crystals doped with low concentrations of holmium, erbium, and thulium ions are investigated. These crystals are attractive as active laser media for developing planar waveguides for near and mid-IR spectral regions. It is shown that, by varying the concentration of impurity rare-earth ions in SrF2 crystals, it is possible to increase and control the refractive index of the medium. This allows one to develop planar waveguides with the core and shell of the same fluoride and control theirs numerical aperture and the number of excited modes. The design of single mode planar waveguide is calculated and proposed for the wavelength of 2 um.

Ag nanoparticles localised surface plasmon field regulated spectral characteristics of Ho3+-doped phosphate-based glass-ceramic

The holmium ion (Ho3+)- activated phosphate-based glass-ceramics with silver nanoparticles (Ag NPs) inclusion were prepared using the standard melt-quenching. The samples were characterised to evaluate the effects of different Ag NPs contents on their structure, microstructure and optical properties. The XRD pattern of the as-quenched samples revealed their glass-ceramic nature. The FTIR and Raman analyses showed the modification of the glass-ceramics network structure due to the embedment of Ag NPs. The TEM and HRTEM images together with the localized surface plasmon resonance (LSPR) absorption bands of the glass-ceramics confirmed the existence of Ag NPs inside the host matrix. The complex impedance analyses of the glass-ceramics suggested the glassy phase dominance in the host network. The photoluminescence (PL) peak intensities were significantly enhanced due to the influence of Ag NPs enabled LSPR effects. The PL decay curve analysis of the glass-ceramics indicated the effect of Ag NPs mediated amplified local electric field and energy transfer from the Ag NPs to Ho3+, a mechanism responsible for the optical traits improvement. The achieved branching ratio and stimulated emission cross-section of the optimum glass-ceramic for the three PL peaks were 73.88% and 46.68 × 10−21 cm2 (green); 83.97% and 41.12 × 10−21 cm2 (red); and 71.40% and 36.95 × 10−21 cm2 (IR). Based on the obtained findings, a structural-optical correlation was established.

Spectral features of Ho3+ -doped boro-phosphate glass-ceramics: Role of Ag nanoparticles sensitization

The development of the metallic nanoparticles-sensitised and lanthanides-doped multi-functional luminescent glass-ceramics (GCs) for advanced applications remains challenging. In this perception, the role of varying silver nanoparticle (Ag NP) concentration on the structures, microstructures and optical properties of some new class of zinc-sulfo-boro-phosphate GCs activated with holmium ions (Ho3+) was analysed using different mechanisms. These GCs were prepared by the standard melt-quenching and thoroughly characterised using various analytic means. The XRD patterns of the as-quenched samples confirmed their GC nature. The Judd–Ofelt (J–O) intensity parameters and radiative properties plus the CIE colour coordinates for these GCs were evaluated using the measured photoluminescence (PL) spectral data. The absorption spectra of the GCs revealed 13 peaks associated to the Ho3+ transitions and the absorption edge data were used to calculate the optical band gap and Urbach energy. The PL spectra of the titled GCs revealed an intense green and red emission peak distinctive of the electronic transitions in Ho3+. Despite the strong mediation of the Ag NPs LSPR on the PL emission of Ho3+, the structural alterations in the GCs network played a dominant role towards the PL peak intensity quenching. The density, Raman, FTIR and impedance spectral analyses exhibited the formation of more bridging oxygen and significant reduction of the nonbridging oxygen in the GC matrix due to the addition of Ag NPs, leading to the Ho3+ clustering. An interrelationship between the structural and optical attributes in these GCs was ascertained for the first time. The proposed GC compositions are established to be beneficial for the advancement of the novel luminescent materials for various photonic and optoelectronic applications.

Intermolecular Coulombic Decay in Endohedral Fullerene at the 4d→4f Resonance

Intermolecular processes offer unique decay mechanisms for complex systems to internally relax. Here, we report the observation of an intermolecular Coulombic decay channel in an endohedral fullerene, a holmium nitride complex (Ho_{3}N) embedded within a C_{80} fullerene, between neighboring holmium ions, and between the holmium complex and the carbon cage. By measuring the ions and the electrons in coincidence after XUV photoabsorption, we can isolate the different decay channels, which are found to be more prevalent relative to intra-atomic Auger decay.

Structure, luminescence and energy transfer of fluoroindate glasses co-doped with Er3+/Ho3+

This work reports on the analysis of structural and spectroscopic properties of the fluoroindate glasses co-doped with Er3+/Ho3+. Structural analysis showed that erbium and holmium ions were modifier ions and depolymerizedof the fluoroindate glass network. The energy transfer processes between rare - earth ions in fluoroindate glasses pumped by and 980 nm laser diode have been also examined. Due to partial Er3+ → Ho3+ energy transfer and superposition of Er3+: 4I11/2 → 4I13/2 (2.77 μm)+ Ho3+: 5I6 → 5I7 (2.85 μm) radiative transitions in fluoroindate glass co-doped with 0.8ErF3/1.6HoF3, a broadening 3 μm luminescence (Δλ= 201 nm) was obtained. The overall energy transfer efficiency ηET1 + ηET2 was calculated to be 95% indicating efficient sensitization of the holmium ions by erbium.

Electroreduction of Holmium Chloride in the Equimolar NaCl–KCl Melt

Rare-earth metals and their alloys are widely used in various engineering fields due to their unique physical and chemical properties. To prepare rare-earth-containing coatings, data on the kinetics of electrode processes with the participation of the rare-earth metals in salt molten media should be available. These problems are poorly understood for rare-earth metals. In the present study, the kinetic parameters of the cathode reduction (transfer coefficient, heterogeneous charge transfer rate constants) of holmium ions in the equimolar NaCl–KCl melt are determined in a temperature range of 1073–1173 K in a holmium chloride concentration range of 1–10 wt % using chronopotentiometry and chronovoltammetry. The dependences of the kinetic parameters on the temperature and concentration of rare-earth metal chloride are determined. The following reduction mechanism of complex ion in the aforementioned melts is suggested: $${\text{HoCl}}_{6}^{{3 - }}$$ = $${\text{HoCl}}_{4}^{ - }$$ + 2Cl–, $${\text{HoCl}}_{4}^{ - }$$ + e → $${\text{HoCl}}_{4}^{{2 - }}.$$

Slow relaxation of two dimensional salen type lanthanide coordination polymer

Reactions of N,N′-bis(salicylidene)-1,2-cyclohexanediamine (H2L) with mixed lanthanide counterions of LnCl3·6H2O and Ln(NO3)3·6H2O afford four lanthanide coordination polymers, e.g. {Dy(H2L)1.5(NO3)3]·5CHCl3·CH3OH}n (1) and {[Ln(H2L)1.5(NO3)2Cl]·2CH2Cl2}n [Ln = Ho (2), Er (3) and Lu (4)]. X-ray crystallographic analysis reveals that H2L effectively function as a bridging ligand possessing two-dimensional (2D) network frameworks. Magnetic analysis reveals that complex 1 exhibits slow magnetic relaxation. The luminescence of complex 1 exhibits luminescence of the ligand, complex 2 and 3 show characteristic near-infrared (NIR) emission of holmium(III) and erbium(III) ions.

Theranostic nanobubble encapsulating a plasmon-enhanced upconversion hybrid nanosystem for cancer therapy.

Nanobubble (NB), which simultaneously enhances ultrasound (US) images and access therapeutic platforms, is required for future cancer treatment.Methods: We designed a theranostic agent for novel cancer treatment by using an NB-encapsulated hybrid nanosystem that can be monitored by US and fluorescent imaging and activated by near-infrared (NIR) light. The nanosystem was transported to the tumor through the enhanced permeability and retention effect. The hybrid nanosystem comprised upconversion nanoparticle (UCNP) and mesoporous silica-coated gold nanorod (AuNR@mS) with the photosensitizer merocyanine 540 to realize dual phototherapy.Results: With the NIR light-triggered, the luminous intensity of the UCNP was enhanced by doping holmium ion and emitted visible green and red lights at 540 and 660 nm. The high optical density state between the UCNP and AuNR@mS can induce plasmonic enhancement to improve the photothermal and photodynamic effects, resulting in cell death by apoptosis. The nanosystem showed excellent stability to avoid the aggregation of nanoparticles during the treatment. JC-1 dye was used as an indicator of mitochondrial membrane potential to identify the mechanism of cell death. The results of in vitro and in vivo analyses confirmed the curative effect of improved dual phototherapy.Conclusion: We developed and showed the therapeutic functions of a novel nanosystem with the combination of multiple theranostic nanoplatforms that can be triggered and activated by 808 nm NIR laser and US.

Customized physical and structural features of phosphate-based glass-ceramics: role of Ag nanoparticles and Ho3+ impurities

The effects of silver nanoparticles (Ag NPs) embedment on the physical and structural characteristics of the holmium ions (Ho3+) activated phosphate-based glass-ceramics were assessed. Two series of such glass-ceramics were prepared using the melt-quenching and characterized. In the first series, the Ag NPs were nucleated from the incorporated AgCl via the redox process. In the second series, the pure Ag nanopowder was directly added. The overall properties of these glass-ceramics were strongly sensitive to the cooling procedure and NPs addition strategies, leading to different density and refractive index modifications in the two series. The recorded O1s XPS peaks were exploited to determine the bridging to non-bridging oxygen ratios in the studied glass-ceramics network that enabled to unfold the differences in the observed inferences. A compelling correlation among various attributes in the achieved glass-ceramics was established. Briefly, the overall traits of the proposed glass-ceramics were tailored by regulating the preparation conditions.

Tunable greenish to reddish luminescence and two-way energy transfer in Ho3+ and Pr3+ doped TeO2:ZnO glass

Holmium and praseodymium co-doped TeO2:ZnO glass were prepared and their luminescent properties investigated. Blue, green, red and NIR luminescence under 355 and 443 nm excitation is observed. Emission spectra showed a decrease in Ho3+ emissions intensities when Pr3+ was added to the host matrix at 355 nm excitation, while for 443 nm excitation one observed a decrease in Pr3+ emissions with holmium ions addition, suggesting a two-way donor/acceptor energy transfer process. The recorded lifetime for Ho3+ emission at 545 nm (5F4 – 5I8) decreases with increasing Pr3+ content under 355 nm excitation. A similar behavior was detected for Pr3+ emission at 488 nm (3P0 – 3H4) due to the holmium content increase when one used a 443 nm excitation. The chromaticity coordinates were obtained from the emission spectra and analyzed in the Commission International de I'Eclairage (CIE-1931) color diagram. Tunable greenish to red overall luminescence was observed. Color tunability within the green-yellow-orange-red region was achieved combining holmium and praseodymium active ion content in the TeO2:ZnO glass, suggesting that the phosphor herein reported is a potential candidate for application in W-LEDs devices.

Growth, structure and physico-chemical properties of monocrystalline ZnCr2Se4:Ho prepared by chemical vapour transport

ZnCr2Se4 single crystals doped with holmium ions having concentrations of 0.032, 0.055 and 0.084 (occupying octahedral positions) were successfully synthesised using chemical vapour transport. The crystals were characterised using various method: scanning electron microscopy (SEM), X-ray diffraction (XRD), SQUID and QD-PPMS measurements, and thermal analysis (DSC/TG). The ac and dc magnetic measurements as well as the specific heat studies with an increasing holmium content showed: 1) antiferromagnetic order with the Néel temperature of TN = 22 K, 2) positive value of the paramagnetic Curie-Weiss temperature increasing from θ = 53 to θ = 100 K, 3) a slight decrease in both the critical field Hc1 characteristic for a metamagnetic transition and the critical field Hc2 corresponding to the breakdown of the helical spin arrangement, 4) the magnetic contribution to the specific heat visible on the sharp peak at TN, which is strongly shifted to much lower temperatures as the magnetic field increases, and 5) the quite significant Sommerfeld gamma coefficient suggesting the properties of the heavy fermion of the single crystal under study. These effects are interpreted in terms of the exchange integrals including non-stoichiometry, spin and structural defects. The DSC/TG analysis confirmed thermal stability of obtained single crystals.

Solution Equilibria of Holmium(III) and Gadolinium(III) Complexes of Thymoquinone

The complexing capacities of thymoquinone with trivalent holmium(III) and gadolinium(III) metal ions and their overall stability constants in aqueous solutions were obtained using the HYPERQUAD 2008 program from the pH-potentiometric titration data. The molecular structures of thymoquinone—metal complexes formed in solutions were determined based on some spectral methods, and molecular modeling. The graphic representation of the complex species concentration curves is given by the distribution diagram performed by means of the HySS 2009 modeling program, which furnishes a variety of data presentations, including tables of concentrations of all species present in solution in the selected pH ranges.

Fast triethylamine gas sensing response properties of Ho-doped SnO2 nanoparticles

Doping is benefical to the formation of defects on the surface and modification of the electronic structure of metal oxides. In this work, SnO2 nanoparticles (NPs) with different holmium ions concentrations of 0 at.%, 0.11 at.%, 0.45 at.%, and 0.53 at.% have been synthesized by a gas-liquid phase chemical deposition method with following annealing process. The SnO2:Ho3+ NPs exhibit superior triethylamine (TEA) gas sensing properties. The TEA sensing performance of the 0.45 at.% Ho-doped SnO2 NPs based sensor markedly improve compared with other different Ho doped based sensors. The response time for detecting 50 ppm TEA is only 2 s, and the response value is about 12. The as fabricated sensor shows fast response, excellent selectivity and reproducibility to TEA gas at a relatively low working temperature of 175 °C. Gas sensing testing shows that a suitable concentration of Ho doping leads to the enhancement of the sensor response. The enhanced sensing mechanism is attributed to the formation of oxygen vacancies and change of carrier concentration.

Metal-Organic Frameworks as Playgrounds for Reticulate Single-Molecule Magnets.

Achieving fine control on the structure of metal-organic frameworks (MOFs) is mandatory to obtain target physical properties. Herein, we present how the combination of a metalloligand approach and a postsynthetic method is a suitable and highly useful synthetic strategy to success on this extremely difficult task. First, a novel oxamato-based tetranuclear cobalt(III) compound with a tetrahedron-shaped geometry is used, for the first time, as the metalloligand toward calcium(II) metal ions to lead to a diamagnetic CaII-CoIII three-dimensional (3D) MOF (1). In a second stage, in a single-crystal-to-single-crystal manner, the calcium(II) ions are replaced by terbium(III), dysprosium(III), holmium(III), and erbium(III) ions to yield four isostructural novel LnIII-CoIII [Ln = Tb (2), Dy (3), Ho (4), and Er (5)] 3D MOFs. Direct-current magnetic properties for 2-5 show typical performances for the ground-state terms of the lanthanoid cations [7F6 (TbIII), 6H15/2 (DyIII), 5I8 (HoIII), and 4I15/2 (ErIII)]. Analysis of the χMT data indicates that the ground state is the lowest MJ value, that is, MJ = 0 (2 and 4) and ±1/2 (3 and 5). Kramers' ions (3 and 5) exhibit field-induced emergent frequency-dependent alternating-current magnetic susceptibility signals, which is indicative of the presence of slow magnetic relaxation typical of single-molecule magnets.