Transition Of Tm Research Articles

Growth, structure and spectroscopic properties investigation on a novel Tm3+-doped disordered Ca(GdxY1-x)Al3O7 hybrid melilite crystal

A disordered Tm3+-doped Ca(GdxY1-x)Al3O7 hybrid melilite crystal (Tm:CGYAM) was successfully grown by using the optical floating zone method, and its structure and spectroscopic properties were studied thoroughly. Structure analysis shows that the Tm:CGYAM crystallizes in tetragonal system. The maximum phonon energy of Tm:CGYAM crystal is estimated to be 765.8 cm−1. Absorption spectrum shows that the absorption cross-section of the Tm:CGYAM crystal is 0.44 ×10−20 cm2 at 788.5 nm, with a FWHM of 34.5 nm. The radiative lifetime of Tm3+:3F4→3H6 transition in Tm:CGYAM crystal is calculated to be 5.35 ms by J-O analysis. The emission cross-sections are 0.321×10−20 cm2 at 1785 nm and 0.324×10−20 cm2 at 1945 nm. The FWHM of Tm3+:3F4→3H6 transition emission band reaches 280 nm. By fitting the fluorescence decay curve, the fluorescence lifetime of Tm3+:3F4 level is estimated as 4.55 ms. The gain cross-section of Tm:CGYAM crystal achieves positive in the range of 1771–2200 nm once the population inversion level reaches 10 %. All the experimental results support the Tm:CGYAM crystal can be a promising candidate material for solid state tunable or ultrashort pulse laser application.

Energy transfer mechanism in infrared-emitting NaYGeO4:Tm3+, Ho3+ phosphors

Two series of NaY0.85Tm0.15-xHoxGeO4 (x = 0.005–0.03) and NaY0.85-xTm0.15HoxGeO4 (x = 0.0–0.055) phosphors have been prepared by the citrate technique. According to XRPD study, all the germanates crystallize in olivine structure and have an orthorhombic lattice, space group Pnma, Z = 4. The diffuse reflectance spectra have been measured and the optical band gap has been estimated. Under 808 nm laser diode excitation, the NaYGeO4:Tm3+, Ho3+ samples exhibit luminescence in the range of 1640–2240 nm, which is caused by 3F4 → 3H6 transition in Tm3+ and 5I7 → 5I8 transition in Ho3+ ions. The highest intensity of holmium lines, while maintaining relatively high intensity of thulium lines, was observed for NaY0.82Tm0.15Ho0.03GeO4, NaY0.815Tm0.15Ho0.035GeO4 samples with the Tm3+/Ho3+ ratio close to 5/1. The luminescence decay kinetics has been studied and the rate of energy transfer from Tm3+ to Ho3+ ions has been calculated. The obtained results indicate an effective energy transfer accelerated by migration due to dipole-dipole interaction. The mechanism of excitation and infrared luminescence in NaYGeO4:Tm3+, Ho3+ phosphors has been proposed.

Atomic Transition Probabilities for Ultraviolet and Optical Lines of Tm ii * *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS5-26555 (program GO-15657). This paper also includes data gathered with the 6.5 m Magellan Telescopes

We report new branching fraction measurements for 224 ultraviolet and optical transitions of Tm ii. These transitions range in wavelength (wavenumber) from 2350 to 6417 Å (42,532–15,579 cm−1) and originate in 13 odd-parity and 24 even-parity upper levels. Thirty-five of the 37 levels, accounting for 213 of the 224 transitions, are studied for the first time. Branching fractions are determined for two levels studied previously for comparison to earlier results. The levels studied for the first time are high lying, ranging in energy from 35,753 to 54,989 cm−1. The branching fractions are determined from emission spectra from two different high-resolution spectrometers. These are combined with radiative lifetimes reported in an earlier study to produce a set of transition probabilities and log(gf) values with accuracy ranging from 5% to 30%. Comparison is made to experimental and theoretical transition probabilities from the literature where such data exist. These new log(gf) values are used to derive an abundance from one previously unused Tm ii line in the UV spectrum of the r-process-enhanced metal-poor star HD 222925, and this abundance is consistent with previous determinations based on other Tm ii lines.

In Situ Local Imaging of Ferromagnetism and Superconductivity in RbEuFe4As4.

The coexistence of superconductivity and ferromagnetism is an intrinsically interesting research focus in condensed matter physics, but the study is limited by low superconducting (Tc) and magnetic (Tm) transition temperatures in related materials. Here, we used a scanning superconducting quantum interference device to image the in situ diamagnetic and ferromagnetic responses of RbEuFe4As4 with high Tc and Tm. We observed significant suppression of the superfluid density in the vicinity of the magnetic phase transition, signifying fluctuation-enhanced magnetic scatterings between Eu spins and Fe 3d conduction electrons. Intriguingly, we observed multiple ferromagnetic domains that should be absent in an ideal magnetic helical phase. The formation of these domains demonstrates a weak c-axis ferromagnetic component probably arising from the Eu spin-canting effect, indicative of possible superconductivity-driven domain Meissner and domain vortex-antivortex phases, as revealed in EuFe2(As0.79P0.21)2. Our observations highlight that RbEuFe4As4 is a unique system that includes multiple interplay channels between superconductivity and ferromagnetism.

Assessment of NIR-triggered PEG-coated NaGdF4:Tm3+/Yb3+ bio-compatible upconversion nanoparticles for contrast enhancement in OCT imaging and optical thermometry

In this investigation, we embarked on the synthesis of polyethylene glycol coated NaGdF4:Tm3+/Yb3+ upconversion nanoparticles (UCNPs), aiming to assess their utility in enhancing image contrast within the context of swept source optical coherence tomography (OCT) and photo-thermal OCT imaging. Our research unveiled the remarkable UC emissions stemming from the transitions of Tm3+ ions, specifically the 1G4 → 3H6 transitions, yielding vibrant blue emissions at 472 nm. We delved further into the UC mechanism, meticulously scrutinizing decay times and the nanoparticles′ capacity to convert radiation into heat. Notably, these nanoparticles exhibited an impressive photo-thermal conversion efficiency of 37.5%. Furthermore, our investigations into their bio-compatibility revealed a promising outcome, with more than 90% cell survival after 24 h of incubation with HeLa cells treated with UCNPs. The nanoparticles demonstrated a notable thermal sensitivity of 4.7 × 10−3 K−1 at 300 K, signifying their potential for precise temperature monitoring at the cellular level.

Thulium-doped titanate-germanate glasses for infrared photonics

In this paper, we performed a comparative spectroscopic analysis of Tm3+-doped glasses based on GeO2-BaO-Ga2O3 (GBG) and TiO2-GeO2-BaO-Ga2O3 (TGBG) to achieve broadband luminescence at 1.8 μm. Glasses were prepared at different doping concentrations (0.05 mol% and 1mol%) in order to investigate the effect of Tm3+ ions as well as host composition (GeO2:TiO2 molar ratios) on near-IR luminescence properties. We report on the hypersensitivity of the transition 3H6 → 3F4 of Tm3+ in a series of titanate-germanate glasses, which was shifted to longer wavelengths with increasing TiO2 concentration. The relative intensity of the main near-IR emission band corresponding to the 3F4 → 3H6 (1.8 μm) transition of Tm3+ was 4.8-fold enhanced for glass with molar ratio GeO2:TiO2 = 1:5 compared to GBG glass system. We observed the luminescence quenching phenomena for samples containing more than 0.5 mol% of Tm3+ ions. The calculated spectroscopic parameters, such as measured luminescence lifetime (τm) and the quantum efficiency (η), were discussed and compared to the different laser glasses. Importantly, luminescence decay curves have been examined using the Inokuti-Hirayama model. Additionally, the correlation between optical properties and local structure in glasses was well evidenced by Raman spectroscopy. The proposed strategy, in combination with various chemical composition of glass host activated by various Tm2O3 concentration, might be beneficial for modern near-infrared photonics.

Cascade laser optimization for 3H4 → 3H5 and 3F4 → 3H6 sequent transitions in Tm3+-doped materials.

We study a cascade laser scheme involving the 3H4 → 3H5 and 3F4 → 3H6 consecutive transitions in Tm3+-doped materials as a promising technique to favor laser emission at 2.3 µm. We examine the conditions in terms of the Tm3+ doping levels for which the cascade laser is beneficial or not. For this, Tm:LiYF4 lasers based on crystals with several doping levels in the range of 2.5 - 6 at.% with and without cascade laser are studied. For low doping of 2.5 at.% Tm3+, adding the laser emission at 1.9 µm allows to double the output power at 2.3 µm, whereas for high doping of 6 at.%, allowing the laser to operate at 1.9 µm totally suppresses the laser emission at 2.3 µm. An analytical model is developed and confronted with experimental results to predict this doping-dependent phenomenon and forecast the potential benefits. This study of cascade laser emission on the 3H4→ 3H5 and 3F4→ 3H6 transitions versus the Tm3+ doping level is finally extended to other well-known Tm3+-doped laser materials.

Luminescence of isoelectronic lanthanide pairs (Ln2+/Ln3+): A relative compression factor for isoelectronic Ln 4fn levels

Luminescent trivalent lanthanides (Ln3+) are utilised extensively in photonic and optoelectronic devices. Luminescent divalent lanthanides (Ln2+) are less frequently applied, despite their desirable 5d electronic properties and similar 4f electronic properties. We report on the luminescence of several isoelectronic lanthanide pairs (Ln3+/Ln2+) that possess the same 4fn configurations but different nuclear charges. The intraconfigurational and interconfigurational transitions of divalent Nd, Sm, Eu, Dy, Ho, Tm and Yb in NaMgF3 are compared to those transitions of trivalent counterparts in NaMgF3 and similar hosts. The 4fn(2S+1LJ) levels of Ln2+ ions are compressed by a factor ξ, relative to the isoelectronic Ln3+. The factor varies within each 4fn configuration with the energy of excited 2S’+1LJ’ states. We define an alternative factor ξ′ that corrects for the intra-ion dependence by introducing a power law dependence on the excited state energies. The inter-ion dependence correlates with the spin-orbit coupling parameters of the isoelectronic ions.

Excited-state absorption and upconversion pumping of Tm3+-doped potassium lutetium double tungstate.

We report on a bulk thulium laser operating on the 3H4 → 3H5 transition with pure upconversion pumping at 1064 nm by an ytterbium fiber laser (addressing the 3F4 → 3F2,3 excited-state absorption (ESA) transition of Tm3+ ions) generating 433 mW at 2291 nm with a slope efficiency of 7.4% / 33.2% vs. the incident / absorbed pump power, respectively, and linear laser polarization representing the highest output power ever extracted from any bulk 2.3 µm thulium laser with upconversion pumping. As a gain material, a Tm3+-doped potassium lutetium double tungstate crystal is employed. The polarized ESA spectra of this material in the near-infrared are measured by the pump-probe method. The possible benefits of dual-wavelength pumping at 0.79 and 1.06 µm are also explored, indicating a positive effect of co-pumping at 0.79 µm on reducing the threshold pump power for upconversion pumping.

Structural, electronic and optical properties of BaRE6(Ge2O7)2(Ge3O10) (RE = Tm, Yb, Lu) compounds and BaYb6(Ge2O7)2(Ge3O10):Tm3+ and BaLu6(Ge2O7)2(Ge3O10):Yb3+,Tm3+ phosphors: potential applications in temperature sensing.

A new series of BaRE6(Ge2O7)2(Ge3O10) (RE = Tm, Yb, Lu) germanates and activated phases BaYb6(Ge2O7)2(Ge3O10):xTm3+ and BaLu6(Ge2O7)2(Ge3O10):12yYb3+,yTm3+ have been prepared using a solid-state reaction. An XRPD study has revealed that the compounds crystallize in the monoclinic system (space group P21/m, Z = 2). The crystal lattice consists of zigzag chains of edge-sharing distorted REO6 octahedra, bowed trigermanate [Ge3O10] units, [Ge2O7] groups, and eight-coordinated Ba atoms. The density functional theory calculations have confirmed a high thermodynamic stability of the synthesized solid solutions. According to the results of vibrational spectroscopy studies and diffuse reflectance measurements, the BaRE6(Ge2O7)2(Ge3O10) germanates are promising compounds for the creation of efficient lanthanide ion activated phosphors. Under 980 nm laser diode excitation, the BaYb6(Ge2O7)2(Ge3O10):xTm3+ and BaLu6(Ge2O7)2(Ge3O10):12yYb3+,yTm3+ samples exhibit upconversion luminescence corresponding to the characteristic 1G4 → 3H6 (455-500 nm), 1G4 → 3F4 (645-673 nm) and 3H4 → 3H6 (750-850 nm) transitions in Tm3+ ions. Heating of the BaLu6(Ge2O7)2(Ge3O10):12yYb3+,yTm3+ phosphor with the optimal composition up to 498 K leads to the enhancement of a broad band at 673-730 nm, caused by 3F2,3 → 3H6 transitions. It has been revealed that the fluorescence intensity ratio between this band and the band at 750-850 nm may be used for temperature sensing. The absolute and relative sensitivities in the studied temperature range reach 0.021% K-1 and 1.94% K-1, respectively.

Coprecipitation synthesis, structural, optical properties, and thermometry application of Tm3+/Yb3+ co-doped YPO4 phosphor

Coprecipitation synthesis and characterization of upconverting YPO4: Tm3+, Yb3+ phosphor is reported in the present work. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Scanning electron microscopy (SEM) were used to examine the structure and morphology of the synthesized phosphor. Tm3+ and Yb3+ co-doped YPO4 material have the tetragonal xenotime crystal structure of space group I41/amd. Upconversion luminescence properties of prepared phosphor are studied under the near-infrared (NIR) 980 nm laser excitation. The intense emission peaks are observed at ∼473 nm and ∼796 nm due to electronic transitions (1G4→3H6) and (3H4→3H6), respectively, and relatively weak emission peaks are observed at 654 nm and 700 nm which are attributed to (1G4→3F4) and (3F2,3→3H6) transitions of Tm3+, respectively. Tm3+ (0.3 mol%)/Yb3+(10 mol%) is the optimized concentration that gives intense and sharp emission in NIR (∼796 nm) region. Power dependence studies have been done to understand the upconversion emission mechanism. The fluorescence intensity ratio of (3F2,3→3H6)/(3H4→3H6) transitions of Tm3+ in the temperature range 323 K–598 K is analyzed. Relative and absolute temperature sensitivity are also calculated. Maximum relative sensitivity is 1.86% K−1 at 323 K and absolute sensitivity increases with rising temperature. Excellent sensitivity, avoidable spectral overlap, and intense upconversion emission, in the first biological window under NIR excitation, show that the prepared material is multifunctional and may have potential applications in temperature sensing and optical heaters for bio-molecules.

Luminescence property in Er3+/Tm3+/Ag NPs doped tellurite glass applied for broadband amplifier

In this study, tellurite glasses co-doped with Er3+/Tm3+ were synthesized through the melt-quenching technique. Under 808 nm excitation, the spectral overlap of 1.53 µm band fluorescence generated by the transition of Er3+:4I13/2→4I15/2 and 1.47 µm band fluorescence generated by the transition of Tm3+:3H4→3F4 achieved the near-infrared (NIR) broadband flat fluorescence emission in the range of 1350–1650 nm, in which the most flat fluorescence emission was achieved when the doping amount of Er2O3 and Tm2O3 was 0.1 and 0.8 mol%, respectively, and the full width at half maximum (FWHM) reached 161 nm. Subsequently, the NIR fluorescence intensity was enhanced by introducing silver nanoparticles (Ag NPs) based on broadband flat fluorescence emission. The optimal conditions conducive to broadband fluorescence enhancement were explored by changing the heat-treated time that could affect the formation and growth of Ag NPs. When the amount of AgCl is 0.5 mol%, tellurite glass co-doped with Er3+/Tm3+ ions heat-treated at temperature 410 ℃ for 6 h has the best enhancement effect of 81 %. After transmission electron microscopy (TEM) measurement, the introduced Ag NPs’ diameter at this time is about 18 nm. Some important spectral parameters of Er3+ and Tm3+ ions, for instance the radiative transition probability together with radiative lifetime were calculated from the absorption spectra according to the Judd-Ofelt theory. Structural characteristics based on X-ray diffraction analysis and thermal stability based on differential scanning calorimeter analysis was presented. Based on the above research, the enhanced broadband and flat fluorescence in the 1350–1650 nm range is of great significance for the application of broadband optical amplifiers in modern WDM networks.

An approach to weld dissimilar polycarbonate and high-density polyethylene by friction stir spot welding

The friction stir spot welding of polymeric materials has been examined extensively; conversely, only a few researchers have addressed the friction stir spot welding of dissimilar polymers. In this study, the possibility of friction stir spot welding of dissimilar polycarbonate to high-density polyethylene is examined, which has not been previously investigated. The influence of welding parameters, namely, tool rotational speed and dwell time, was investigated experimentally, whereas the plunging depth, plunging rate, and tool geometry were kept constant during all tests. The induced temperature and the weld lap shear force were recorded and analyzed. Both materials are welded successfully by friction stir spot welding. At 2300 rpm and 40 s dwell time when the polycarbonate sheet was on the top, the maximum lap shear force of 0.37 kN was obtained. The findings demonstrated that an effective weld might be attained at a moderate frictional heating temperature slightly below the melting temperature Tm and glass transition temperature Tg of both welded materials. At very low temperatures, poor weld quality was obtained. When temperatures extensively increased, the results deteriorated to exhibit weak joint lap shear values because of the presence of cavities and pores in the weld junction.

Synthesis and characterization of liquid crystalline poly(ether-ketone)s containing 1-benzyl-4-piperidone moiety as a pendent group

A series of poly(ether-ketone)s (PEKs) having 1-benzy-4-piperidone moiety as a pendant group was successfully synthesized from 3,5-bis(3-ethoxy-4-hydroxybenzyldehyde)-1-benzyl-4-piperidone and various dibromoalkanes employing solution polycondensation method. The structures of the novel monomer, model compound, and PEKs were characterized using FT-IR, 1H NMR, and mass Spectroscopy. The thermal and liquid crystalline properties of the synthesized polymers were evaluated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The study revealed that all of the prepared polymers are thermally stable. The glass transition temperature, Tg, was in the range of 46–117 °C, and the temperature that caused a 5% weight loss was over 290 °C. DSC profiles of PEKs with aliphatic spacer lengths 4 and 8 revealed both melting transition, Tm, and isotropization transition, Ti, peaks. These results indicate that the polymers possess a thermotropic liquid crystal structure. An optical microscopy study called polarized optical microscopy (POM) confirmed that these polymers have features of liquid crystals. Threaded and droplet textures could be seen under POM.

Synthesis, optical and thermoluminescence properties of thulium-doped KMgF3 fluoroperovskite

KMgF3 fluoroperovskite doped with thulium at different concentrations were synthesized by the solid-state reaction method. The phase composition and the thermal stability up to 600 °C of the polycrystals were analyzed by X-ray diffraction and thermogravimetric analysis, respectively. The KMgF3 at 1.0 mol% of Tm polycrystals showed the best thermal stability and did not present another phase. The gamma radiation (0.1–10 kGy) effect in thulium-doped KMgF3 produced the F color centers, and their aggregates such as F2, and F3 centers. The F centers, and the potassium vacancies (VK−) in the fluoroperosvkites were analyzed by the optical absorption and emission measurements. Optical absorption at 275 nm and 443 nm were assigned to F and F2, respectively, in undoped KMgF3. Tm-doped fluoroperovskite shows the optical absorption bands at 277, 393, 432, and 577 nm, which were ascribed to the F, F3, F2 and VK− centers, respectively. When the F band for undoped polycrystals was excited at 275 nm, a clear emission associated with F2 and F3 centers was observed. In the case of Tm-doped, an enhancement of the blue emission at 457 nm occurred and a UV band (354 nm) was observed upon exciting the F band. The blue emission of thulium was overlapped with the F3 color center band. The emission bands at 457 and 354 nm were ascribed to 1D2 - 3F4 and 1D2 - 3H6 transitions of Tm in KMgF3. The optical absorption and glow curves were investigated too. The glow curves were assisted by the color centers, vacancies, and thulium impurity. Thermal bleaching shows that the F center was the main participant to give rise to the TL intensity of the glow curves. Thulium acts as a deep electron trap in the bandgap of the KMgF3 fluoroperovskites forming TL peak at the higher temperature, from 430 to 408 °C. The absorption, emission, and thermoluminescence glow peaks of the undoped and Tm-doped KMgF3 were compared.

Optical coherence and energy-level properties of a Tm3+ -doped LiNbO3 waveguide at subkelvin temperatures

We characterize the optical coherence and energy-level properties of the 795 nm $^3$H$_6$ to $^3$H$_4$ transition of Tm$^{3+}$ in a Ti$^{4+}$:LiNbO$_{3}$ waveguide at temperatures as low as 0.65 K. Coherence properties are measured with varied temperature, magnetic field, optical excitation power and wavelength, and measurement time-scale. We also investigate nuclear spin-induced hyperfine structure and population dynamics with varying magnetic field and laser excitation power. Except for accountable differences due to difference Ti$^{4+}$ and Tm$^{3+}$-doping concentrations, we find that the properties of Tm$^{3+}$:Ti$^{4+}$:LiNbO$_{3}$ produced by indiffusion doping are consistent with those of a bulk-doped Tm$^{3+}$:LiNbO$_{3}$ crystal measured under similar conditions. Our results, which complement previous work in a narrower parameter space, support using rare-earth-ions for integrated optical and quantum signal processing.

Two steps enhancement of dual mode (UC and DS) behaviour of Ho3+/Yb3+ and Tm3+/Yb3+ co-doped GdVO4 phosphors: Improvement in spectral and color purity

In the present work, the dual mode (Upconversion and Downshifting) emission behavior of Tm3+/Yb3+ and Ho3+/Yb3+ co-doped GdVO4 phosphors synthesized via high temperature solid state reaction technique have been studied. The pure phase formation has been confirmed by X-rays diffraction (XRD) studies. The crystalline nature has been found to improve on calcining the phosphors at 1473 K and also by incorporation of TiO2. The surface particles’ shape and size have been studied by SEM technique. The vibrational behaviour of the vanadate host has been investigated by Fourier Transform Infrared (FTIR) measurements. The UV–vis absorption spectra show the formation of charge transfer band (CTB) in UV region due to (VO4)3 group. The non-linear upconversion (UC) spectra show intense blue and NIR emission in GdVO4: Tm3+/Yb3+ phosphor on excitation with 980 nm radiation, whereas intense green and red UC emissions are observed in GdVO4: Ho3+/Yb3+ phosphor. The downshifting (DS) behaviour has been investigated in both the phosphors which show the self activation behaviour of GdVO4 host along with some sharp peaks in blue and green regions due to f-f transitions in Tm3+ and Ho3+ ions. The dual mode (UC and DS) emission has been further improved on heating the samples at higher temperatures and also by incorporation of TiO2. The color of the phosphor samples in the UC emission spectra has been visualized by CIE diagram. The color purity enhances in both the phosphors by increasing the calcination temperature and also by addition of TiO2. The spectral purity has been also calculated for the UC emission spectra and its also shows the same trend. Such phosphors are applicable for the display devices in blue, green and red regions via dual mode processes.

A novel high color purity blue-emitting Tm3+-doped β-Ca3(PO4)2-type phosphor for WLED application

The series of Tm-doped phosphates Ca9-xZnxLa0.9(PO4)7:0.1Tm3+ for phosphor-convertible white LEDs (pc-WLED) with β-Ca3(PO4)2-type structure were synthesized using a standard high temperature route. Intense blue emission in the visible spectrum was observed due to 4f-4f transitions in the Tm3+ ion. The phosphates have been characterized by powder X-ray diffraction (PXRD), second harmonic generation (SHG), and luminescence spectroscopy. These phosphors show a satisfactory blue performance due to the 1D2 – 3F4 (≈ 450 nm) transition of Tm3+ excited by near-UV light (358 nm). The crystal structure transforms R3c → R3¯c upon Ca2+ → Zn2+ substitution, and it leads to growing of the integral intensity in 4 times compared with unsubstituted phosphate. Rising of color purity peaking at x = 1 was also observed. The obtained characteristics are superior to than that for the commercial blue phosphor BaMgAl10O17:Eu2+. Generally, Ca9-xZnxLa(PO4)7:Tm3+ phosphates are a new kind of potential blue emitting phosphors for white light-emitting diodes.

AC-electrical conductivity, magnetic susceptibility, dielectric modulus and impedance studies of sol-gel processed nano-NiMgZn ferrites

The Ni0·2Mg0.8-xZnxFe2O4 (x = 0.0–0.8) (NMZF) nanomaterials were prepared via sol-gel technique followed by three calcination temperatures (T) of 400, 450 and 500 °C/5 h. The X-ray diffraction patterns of NMZF showed the single phase cubic spinel structure. The nanosized grains were detected using the field emission scanning electron microscope (FESEM) images. The results showed that the larger concentration of zinc established the maximum grain size (86.9–119.6 nm), wherein the predominant grain boundary creeping mechanism was observed. The electric (Te) and magnetic (Tm) transition temperatures obtained using the Arrhenius and magnetic susceptibility-temperature (χ-T) plots revealed that the transition temperatures were decreased with increase of Zn-content. The Tm (195–250 °C) values obtained for x = 0.8 sample (high Zn-content) at 400 and 500 °C temperatures indicated the decrease of magnetic exchange interactions as well as the weakening nature of ferrimagnetic behavior. Furthermore, in order to identify the diffusion of carriers from one state to other state, the activation energies were calculated using the Arrhenius plots for x = 0.0–0.8 contents. In addition, the frequency and temperature dependence of dielectric modulus and impedance parameters was studied for addressing the relaxation mechanism, grain and grain boundary effect in the electrical conduction mechanism of NMZF. The Nyquist plots showed the presence of non-Debye relaxations for all samples. Besides, the same plots attributed the semiconducting nature at high temperatures due to having the complete semicircular arcs.

Synthesis, structure, photoluminescence, band gap and energy transfer mechanism of a novel bimetallic thulium–mercury compound with a three-dimensional framework

Under hydrothermal conditions, a novel bimetallic thulium–mercury compound {[Tm(H2O)2(IA)3]2n[(Hg6Br13)n]}(nHgBr2)·4nH2O·nH3O (1) (IA = isonicotinato anion) was prepared and the crystal structure was characterized by single-crystal and powder X-ray diffraction. It is characterized by a three-dimensional (3D) framework with a novel two-dimensional (2D) inorganic [(Hg6Br13)n] layer. Solid-state photoluminescence measurements revealed that compound 1 emits upconversion mazarine emission bands, which are originated from the 1G4 → 3H6 and 1D2 → 3H4 characteristic emissions of the 4f electron intrashell transitions of Tm(III) ions. An energy transfer mechanism is reported. Compound 1 displays CIE chromaticity coordinates of 0.1288 and 0.0635 in the mazarine region. A solid-state UV–Vis–NIR diffuse reflectance spectrum unveiled that compound 1 has a wide optical band gap of 2.69 eV. A thermogravimetry analysis measurement is also reported. A novel bimetallic thulium–mercury compound was prepared and characterized. It features a 3D framework with a novel 2D inorganic [(Hg6Br13)n] layer. It contains many mercury(II) ions with four different coordination environments. It emits upconversion mazarine photoluminescence emission peaks, which could be attributed to the 1G4 → 3H6 and 1D2 → 3H4 characteristic emissions of the 4f electron intrashell transitions of the Tm(III) ions. An energy level diagram was used to explain the energy transfer mechanism. It has CIE chromaticity coordinates of 0.1288 and 0.0635 in the mazarine region, and it possesses a wide optical band gap of 2.69 eV.