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This study aimed to obtain and investigate ZnCr2Se4 single crystals doped with rhenium. The single crystals were obtained by applying chemical vapour transport. An X-ray study confirmed the cubic (Fd3¯m) structure of the tested crystals. Thermal, magnetic, electrical, and specific heat measurements accurately determined the physicochemical characteristics, which revealed that the obtained single crystals are p-type semiconductors with antiferromagnetic order below the Néel temperature TN = 21.7 K. The Debye temperature had a value of 295 K. The substitution of Re-paramagnetic ions, possessing a screened 5d-shell, in place of Zn-diamagnetic ions, caused an increase in the activation energy, Fermi energy, and Fermi temperature compared to the pure ZnCr2Se4. The boost of the dc magnetic field induced a shift of TN towards lower temperatures and a spin fluctuation peak visible at Hdc = 40 and 50 kOe. The obtained single crystals are thermally stable up to 1100 °C.

Monocrystalline chalcogenide spinels ZnCr

Oxyfluoride lead-based and lead-free germanate glasses were heat-treated in order to fabricate transparent glass-ceramics. Cubic β-PbF2 nanocrystals are well formed during crystallization of lead germanate glass. The up-conversion luminescence spectra of Er3+ ions in lead germanate glass-ceramic system are enhanced significantly due to partial incorporation of the optically active ions into fluoride crystalline phase. These effects are not significant in oxyfluoride lead-free germanate glass after heat treatment process. The crystallization of barium gallo-germanate glass with BaF2 is more complex and the presence of four crystalline phases BaF2, BaO, Ba3Ga2Ge4O14 and GeO2 was verified by X-ray diffraction measurements.

The new series of single-crystalline chromium selenides, Ta-doped ZnCr2Se4, was synthesised by a chemical vapour transport method to determine the impact of a dopant on the structural and thermodynamic properties of the parent compound. We present comprehensive investigations of structural, electrical transport, magnetic, and specific heat properties. It was expected that a partial replacement of Cr ions by a more significant Ta one would lead to a change in direct magnetic interactions between Cr magnetic moments and result in a change in the magnetic ground state and electric transport properties of the ZnCr2−xTaxSe4 (x = 0.05, 0.06, 0.07, 0.08, 0.1, 0.12) system. We found that all the elements of the cubic system had a cubic spinel structure; however, the doping gain linearly increased the ZnCr2−xTaxSe4 unit cell volume. Doping with tantalum did not significantly change the semiconductor and magnetic properties of ZnCr2Se4. For all studied samples (0 ≤ x ≤ 0.12), an antiferromagnetic order (AFM) below TN~22 K was observed. However, a small amount of Ta significantly reduced the second critical field (Hc2) from 65 kOe for x = 0.0 (ZnCr2Se4 matrix) up to 42.2 kOe for x = 0.12, above which the spin helical system changed to ferromagnetic (FM). The Hc2 reduction can lead to strong competition among AFM and FM interactions and spin frustration, as the specific heat under magnetic fields H < Hc2 shows a strong field decrease in TN.

Novel multicomponent titanate-germanate glasses singly doped with transition metal (Cr3+) and rare earth ions (Eu3+) were synthesized and the glass transition temperatures and thermal stability parameters were determined using DSC measurements. X-ray diffraction analysis confirmed fully amorphous nature of the received samples. Their structural and optical properties were compared with germanate glasses without TiO2. Correlation between local structure and optical properties in titanate-germanate glasses is well evidenced by FT-IR, Raman, EPR, and luminescence spectroscopy. In particular, luminescence spectra and their decays are examined for glass samples, where GeO2 was partially substituted by TiO2.

Lead borate glasses doubly doped with Dy3+–Tb3+ were investigated using optical spectroscopy: photoluminescence and decay time measurements. The main green emission band due to the 5D4→7F5 transition of Tb3+ was observed under excitation of Dy3+. The energy transfer process from Dy3+ to Tb3+ occurs through nonradiative processes. The energy transfer efficiencies and transfer probabilities as a function of a square of the total rare earth ions concentration using Forster method were calculated. The nonlinear behavior of the energy transfer probability and the luminescence intensity ratio for a higher concentration of acceptor was studied taking into account the possible processes: concentration quenching and partial crystallization of the lead borate glasses.

In this work, luminescence properties of Tb 3+ /Sm 3+ co-doped lead borate glasses are examined in details. Luminescence spectra of rare earths were measured under different excitation wavelengths. Characteristic luminescence bands corresponding to electronic transitions of terbium and samarium ions were detected under direct excitation of Tb 3+ . The energy transfer from Tb 3+ to Sm 3+ ions in lead borate glass occurs through a nonradiative process with an efficiency from 0.6% to 16%, depending on samarium concentration. Luminescence decay curves for the 4 G 5/2 state of Sm 3+ ions in lead borate glasses were fitted using the Inokuti-Hirayama model. The concentration-dependent luminescence quenching was explained by the non-radiative energy transfer process between the Sm 3+ ions through the cross-relaxation mechanism. The CIE chromaticity coordinates and correlated color temperatures for Tb 3+ /Sm 3+ co-doped lead borate glasses are also presented and discussed.

Crystal structure, magnetic and specific heat measurements, electrical conductivity, as well as DSC/TG measurements for single-crystalline CdxMnyCrzSe4 (where x + y + z ≈ 3) spinels are presented. The electrical conductivity and dc magnetic susceptibility measurements exhibit thermally activated semiconducting properties and ferromagnetic (FM) order for all compositions below the Curie temperature TC = 130 K, respectively. The long-range FM interactions, defined by the Curie temperature, do not substantially depend on the manganese content, and the nearest neighbour FM interactions, represented by the positive value of the Curie-Weiss temperature, decrease from 183 K to 156 K. Hysteresis loops of all crystals have a very small coercive field (∼18 Oe) and remanence (∼0.09 μB/f.u.) with full saturation above 10 kOe. These effects are interpreted in terms of the superexchange integrals for the first two coordination spheres including spin defects.

Physico-chemical studies of (Zn1–xDyx)Cr2Se4 and Zn[Cr2–xDyx]Se4 spinel systems (x ​= ​0.05, 0.10) containing dysprosium ions in both tetra- and octahedral positions have shown an enhancement of long-range antiferromagnetic interactions and a weakening of short-range ferromagnetic ones. This resulted in the appearance of geometric type spin-glass in connection with the increase in the length of chemical bonds between chromium ions. This state of spin-glass is also due to the large difference in the absolute values of the superexchange integrals and the small magnetic contribution to the specific heat below the freezing point. Studies of XPS and X-ray absorption near edge structure (XANES) showed that no main edge shift was observed between the tetra- and octahedral positions of dysprosium ions, which indicates that they remain in the +III oxidation state. Thus, significant differences between the effective magnetic moment and the effective number of Bohr magnetons, as well as much higher saturation magnetization values above 6 μB, suggest that chromium ions may have a different oxidation state. These effects may be also generated by spin defects.

Nanocrystalline β-PbF2 phase singly-doped with Eu3+ and Tb3+ ions have been successfully synthesized using sol-gel technique and subsequent heat-treatment of xerogels at 350 °C. Thermal behavior and structural properties of obtained materials were studied using thermogravimetric analysis (TG), differential scanning calorimetry (DSC) as well as FT-IR and Raman techniques. XRD results confirmed formation of β-PbF2 nanocrystals embedded in silica amorphous hosts after annealing at 350 °C. Moreover, the photoluminescence properties have been investigated based on excitation and emission spectra as well as decay analysis from the 5D0 (Eu3+) and the 5D4 (Tb3+) excited states. The sharp intraconfigurational 4f6−4f6 and 4f8−4f8 emission transitions assigned as the 5D0→7FJ (J=0–4) of Eu3+ and the 5D4→7FJ (J=6-3) of Tb3+ bands, respectively, were registered. The most prominent bands in studied xerogels and glass-ceramic materials are related to the following electronic transitions: 5D0→7F1 (orange) and 5D0→7F2 (red) (Eu3+) as well as 5D4→7F5 (green) and 5D4→7F6 (blue) (Tb3+). Thus, the R/O (Eu3+) and G/B (Tb3+) luminescence intensity ratios were calculated and analyzed. Luminescence decay kinetic clearly indicated a presence of two different surroundings around Eu3+ and Tb3+ dopants in β-PbF2-based glass-ceramic samples. In such singly-doped with Eu3+ and Tb3+ materials, the longer luminescence lifetimes (Eu3+: τ1(5D0)=0.90 ms, τ2(5D0)=5.15 ms; Tb3+: τ1(5D4)=0.48 ms, τ2(5D4)=4.01 ms) of an appropriate excited states were achieved in comparison to xerogel hosts (Eu3+: τ(5D0)=0.38 ms; Tb3+: τ(5D4)=0.49 ms). The obtained results indicate the incorporation of Eu3+ and Tb3+ ions into nanocrystalline phase during ceramization process.

Chemical compounds with a general formula CuCr2–xMnxSe4 (x = 0.1, 0.2) were successfully synthesized in polycrystalline form, using solid state reaction method, and as nanoparticles, using high-energy ball milling. The influence of manganese and grain size on their structure, magnetic and thermal properties was investigated by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), magnetic measurements (SQUID, high magnetic fields) and DSC (Differential Scanning Calorimetry). Electronic structures of obtained compounds were determined using XANES (X-ray Near Edge Absorption Spectroscopy) and XPS (X-ray Photoelectron Spectroscopy). X-ray studies confirmed that the spinel phase forms only for x = 0.1, 0.2. The obtained compounds crystallize with the space group F d 3 ¯ m . The results of magnetic measurements for poly- and nanocrystalline compounds showed that the polycrystalline compounds are ferromagnets with the Curie temperature of TC =352 K for x = 0.1 and TC =342 K for x = 0.2, and the Curie-Weiss temperature of θCW =362 K for x = 0.1 and θCW =354 K for x = 0.2. Whereas the nanoparticles CuCr2–xMnxSe4 (x = 0.1, 0.2) revealed a superparamagnetic character with blocking temperature of TB ≈ 25 K for both compounds. The XANES and XPS data indicate the Cr ions are trivalent (Cr3+). Mn ions are trivalent and tetravalent (Mn3+ and Mn4+), which implies small amount of the Cu ions change the valency from divalency to monovalency (Cu2+ and Cu1+). DSC/TG analysis indicates that the presence of Mn ions in the CuCr2Se4 crystal lattice affects the stability and resistance of the doped compounds in comparison with the pure CuCr2Se4. Decreasing the grain size leads to a decrease in melting temperature.

Studies carried out by X-ray and thermal analysis confirmed that acetaminophen (paracetamol), declared by the manufacturers as an Active Pharmaceutical Ingredient (API), was present in all studied medicinal drugs. Positions of diffraction lines (2&theta, angles) of the studied drugs were consistent with standards for acetaminophen, available in the ICDD PDF database Release 2008. |&Delta, 2&theta, values were lower than 0.2&deg, confirming the authenticity of the studied drugs. Also, the values of interplanar distances dhkl for the examined samples were consistent with those present in the ICDD. Presence of acetaminophen crystalising in the monoclinic system (form I) was confirmed. Various line intensities for API were observed in the obtained diffraction patterns, indicating presence of the preferred orientation of the crystallites in the examined samples. Thermal analysis of the studied substances confirmed the results obtained by X-ray analysis. Drugs containing only acetaminophen as an API have melting point close to that of pure acetaminophen. It was found that presence of other active and auxiliary substances affected the shapes and positions of endothermal peaks significantly. A broadening of endothermal peaks and their shift towards lower temperatures were observed accompanying an increase in the contents of additional substances being &ldquo, impurities&rdquo, in relation to the API. The results obtained by a combination of the two methods, X-ray powder diffraction (XRPD) and differential scanning calorimetry/thermogravimetry (DSC/TGA), may be useful in determination of abnormalities which can occur in pharmaceutical preparations, e.g., for distinguishing original drugs and forged products, detection of the presence of a proper polymorphic form or too low content of the active substance in the investigated drug.

ZnCr2Se4 spinel single crystals doped with neodymium ions having concentrations of 0.05, 0.08 and 0.10 and occupying tetrahedral positions were synthesized using chemical vapour transport. Thermal analysis as well as electrical conductivity, magnetic isotherm, and magnetic susceptibility measurements showed thermal stability at higher temperatures, semiconducting behavior with a metal-insulator transition at TMI ≥ 330 ​K, an antiferromagnetic order with a Neel temperature TN ​= ​21.5 ​K, a short-range ferromagnetic interactions evidenced by a positive Curie-Weiss temperature θ ​= ​55, 60 and 68 ​K with increasing Nd-content in the sequence 0.05, 0.08 and 0.10, two critical fields Hc1 and Hc2 at 10 and 60 ​kOe, regardless of the Nd-content. The specific heat studies showed more complex magnetic transitions, i.e. two magnetic transitions at TN and at spin-glass temperature (TSG) for the Nd-poorer samples and only one magnetic transition at TN for Nd-richer ones. These effects are interpreted in terms of the superexchange integrals for the first two coordination spheres including chemical bond length and spin fluctuation.

Series of Eu 3+ -doped lead-free germanate and borate glasses were synthesized. The MO glass modifiers (M = Ca, Sr or Ba) were partially or totally substituted by MF 2 in chemical composition. In contrast to samples modified by CaO/CaF 2 or SrO/SrF 2 , the germanate glass samples containing BaO and/or BaF 2 are fully amorphous, while the lead-free borate glasses are fully amorphous, independently from glass modifiers. Effect of glass modifiers on spectroscopic properties of Eu 3+ were systematically investigated. For that reason, excitation and emission spectra of Eu 3+ ions in examined systems were registered. Based on the emission spectra, ratio of integrated luminescence intensity of the 5 D 0 → 7 F 2 transition to that of the 5 D 0 → 7 F 1 transition (R factor) was calculated. Moreover, the luminescence decay curves were collected and the luminescence lifetimes of the 5 D 0 excited state of Eu 3+ ions were determined in function of MF 2 concentration.

Series of lead-free borate glasses with different oxide modifiers and lanthanide ions were prepared. The effect of oxide modifiers MO (M = Ca, Sr, Ba) on spectroscopic properties of trivalent Ln3+ (Ln = Eu, Er, Pr) were systematically investigated. Especially, the luminescence spectra of Ln3+-doped lead-free borate glasses are presented and discussed in relation to the impact of selective components (CaO, SrO and BaO). Several spectroscopic parameters, such as the fluorescence intensity ratio R/O (Eu3+) and measured luminescence lifetimes for the 5D0 (Eu3+), 4I13/2 (Er3+) and 1D2 (Pr3+) excited states of lanthanide ions were analyzed in details. The research proved that spectroscopic properties of trivalent Ln3+ depend significantly on kind of presence oxide modifiers MO (M = Ca, Sr, Ba) in glass host matrices.

The crystal structure, magnetic isotherm, magnetic susceptibility, electrical conductivity and specific heat measurements for single-crystalline Zn x Dy y Cr z Se 4 (where x + y + z ≈3) spinels are presented. A semiconducting behavior with the activation energy of 0.53 eV, an antiferromagnetic order with a Neel temperature T N =22 K and a strong ferromagnetic exchange evidenced by a positive Curie–Weiss temperature θ =79, 71 and 70 K with increasing Dy-content in the sequence 0.05, 0.13 and 0.19 were established. Below T N the magnetic field dependence of magnetization, M(H) , shows two peaks at critical fields H c1 and H c2 . The values of H c1 decrease slightly with temperature, especially for the larger Dy-content, while the values of H c2 drop rapidly with temperature. The magnetic contribution to the specific heat displays a sharp peak at T N , which is strongly shifted to much lower temperatures in the applied magnetic fields. Similar behavior was found for the temperature dependence of the specific heat C(T) plotted as C(T) / T vs. T . The value of the magnetic and phonon contribution to the entropy at T N and at H =0 is only ∼4.8, ∼4.4 and ∼4.2 J mol −1 K −1 /Cr 3+ for y =0.05, 0.13 and 0.19, respectively, much lower than the average magnetic contribution S m =( z /2)Rln(2 S +1)=12.33 J mol −1 K −1 /Cr 3+ calculated for Cr 3+ ion with S =3/2, as the dysprosium one is paramagnetic.

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 Neel 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.

Polycrystalline compounds of the ZnxMnyCrzSe4 system (x + y + z ≈ 3) crystallizing in a cubic spinel structure were successfully synthesized in the concentration range of x = 0.11 ÷ 0.46 using the ceramic method. The influence of manganese on microstructure, magnetic, thermal and electronic properties was investigated. X-ray studies confirmed that the spinel phase forms throughout the entire range (x = 0.1 ÷ 0.5). The results of magnetic measurements showed that the studied compounds are antiferromagnets with the Neel temperature of TN = 12 ÷ 25 K and the Curie-Weiss temperature increasing from θ = 87 K for x = 0.11 to θ = 110 K for x = 0.46. Below TN, the magnetic field dependence of magnetization shows two peculiarities at critical fields Hc1 (connected with metamagnetic threshold accompanied with transition from a helical to a conical phase) and Hc2 (where the conical magnetic structure transforms into a ferromagnetic phase). The values of Hc1 remain almost constant while the values of Hc2 shift into lower magnetic fields as the Mn content increases. These effects are interpreted in terms of the superexchange integrals for the first two coordination spheres including spin defects and non-stoichiometry. The XPS study is consistent with FPLO calculation and discerned Mn2+ charge states. The effects of different concentrations of Zn, Mn and Cr have been demonstrated by XPS experimental results. DSC/TG analysis indicates that the presence of Mn ions in the ZnCr2Se4 crystal lattice affects the stability and resistance of the doped compounds in comparison with the pure ZnCr2Se4.

X-ray analysis confirmed that in all investigated samples, the active API (acetylsalicylic acid and ascorbic acid) was present. The values of the interplanar distance d hkl for the studied samples are in good accordance with those presented in the ICDD database. The intensities of the diffraction lines depend on the content of the component in the tested preparation. Therefore, different intensities of lines for the APIs were observed in the obtained diffraction patterns. Thermal analysis of the studied substances showed that during the thermal analysis, the following phenomena might occur: dehydration and (or) melting, crystalline transformation. Moreover, it was found that the chemical structure of the studied compounds affects the process of their thermal decomposition. The data obtained during these investigations can be useful in quick tests of physicochemical discrepancies and abnormalities between potential components of pharmaceutical preparations. The evidence for the interaction can be obtained by comparing DSC and TG curves of the drug and the excipient, as well as those of their physical mixtures. For this reason, the study of characteristics of thermal decomposition of drugs and excipients is necessary. Based on the above investigations, it may be stated that a combination of two methods: XRPD and DSC can be used to distinguish the original drugs from counterfeit products, e.g., by checking for the presence of the correct API or by a comparison of the drugs fingerprint.

Luminescence properties of Dy3+–Tb3+ co-doped lead borate glasses were investigated. Luminescence spectra were registered under various excitation wavelengths. Characteristic luminescence bands corresponding to transitions of Dy3+ and Tb3+ ions were detected under excitation of trivalent dysprosium. The energy transfer from Dy3+ to Tb3+ ions in lead borate glass occurs through a nonradiative process with an efficiency up to 16%. The presence of energy transfer process was also confirmed by excitation spectra measurements.