Melt Crystallization Method Research Articles

Preparation and scintillation properties of Eu3+-doped high crystallinity tellurite glass ceramics

In this study, a high-crystallinity glass-ceramic scintillator doped with Eu³⁺ containing Bi₂Te₄O₁₁ nanocrystals was prepared using a traditional melt crystallization method. The optimal heat treatment conditions, phase structure, and luminescent properties of the glass-ceramics were systematically investigated using various characterization techniques, including DSC, XRD, SEM, and spectrophotometry. To achieve glass-ceramic samples with high transmittance and excellent luminescent performance, the optimal heat treatment process was determined to be 500 °C for 10 minutes. The final sample was found to have a density of 5.9 g/cm³ and a crystallinity of 70%. Strong orange-red light emission was exhibited by the glass-ceramic under both 465 nm light and X-ray excitation. The maximum integral X-ray excited luminescence (XEL) intensity was found to reach 20.2% of that of the commercial Bi4Ge3O12 (BGO) scintillation crystal. It is indicated by the research that Eu³⁺-doped high-crystallinity tellurate glass-ceramics are promising candidate materials for scintillators in the field of X-ray detection.

Static layer melt crystallization of dimethyl carbonate: Binary thermodynamic phase diagram analysis and process optimization

Dimethyl carbonate (DMC) is one kind of important solvent for lithium battery electrolyte. The purifying method of DMC is crucial for obtaining high purity product of it. Using a green and sustainable technology makes more sense in the face of increasing environmental burdens. In this study, a static layer melt crystallization method was used to achieve the purification of high purity DMC from a mixture of DMC and its major impurities. The partial binary phase diagrams between DMC and the main impurity - methanol (MT) - were determined using differential scanning calorimetry (DSC) method. Effect of process parameters such as crystallization temperature, cooling rate, sweating temperature, and heating rate on the distribution coefficient Kf and yield Y were evaluated using One-factor-at-a-time (OFAT) experiment and response surface experiment, respectively. The phenomenological relationships between different parameters and distribution coefficient and yield were discussed and revealed. Eventually, under the optimized process conditions, the purity of DMC was increased from 96 % to 99.847 %, and the single yield could reach 70 %.

Study on fluorine vacancy defects in yttrium fluoride coating materials

Abstract Rare-earth fluoride coating materials have attracted wide attention as a substitute for ThF4 low-refractive index materials. However, the coating materials and coated films fail to achieve the desired results due to vacancy defects caused by their fluorine-loss decomposition characteristics. To explore the rare earth fluoride coating materials’ fluorine loss influence law, the melt crystallization method is used to simulate the yttrium fluoride (YF3) pre-melting process through the electronic paramagnetic resonance (EPR) obtained at different temperatures under the fluorine vacancy defects change rule. According to the number of unpaired spintrons, the number of spintrons in each vacancy is calculated. The results show that the fluorine vacancy defects increase with the increase of temperature, the formation of YF3 fluorine vacancy defects does not affect the change of crystal structure, and the addition of the additive ammonium hydrogen fluoride (NH4HF2) can reduce the oxygen content of YF3 and effectively inhibit the formation of fluorine vacancy. The effect is gradually obvious with the amount of additives added.

Synthesis and upconversion luminescence properties of Ho3+-Yb3+ co-doped glass ceramics containing LiGd(WO4)2

Ho3+-Yb3+ co-doped glass ceramics containing LiGd(WO4)2 were prepared by melt crystallization method. By using the methods of differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmittance, and scanning electron microscopy (SEM), the optimal heat treatment condition for the samples was identified to be 580 °C/140 min. In these conditions, the transmittance of glass ceramic is about 75 % in the 380–780 nm range. In the upconversion emission spectra, strong green emission (543 nm) and red emission (650 nm) due to 5F4/5S2, 5F5→5I8 transitions are observed at 980 nm excitation. Additionally, the optimum doping concentrations of Ho3+ and Yb3+ were 0.12 % and 0.4 %. The crystal field changes around dopant ions were analyzed using J-O theory and Eu3+ probe to explain the up-conversion luminescence enhancement of glass ceramics containing LiGd(WO4)2. The chrominance coordinates of 0.12 % Ho3+-0.4 % Yb3+ co-doped glass ceramics are located in the green light region, and the color purity is 95.6 %. In summary, Ho3+-Yb3+ co-doped transparent glass ceramics containing LiGd(WO4)2 have potential applications in infrared detection and green solid-state lasers.

Preparation of Eu2+ and Dy3+ co-doped Sr2MgSi2O7 translucent long afterglow glass-ceramics by recrystallization-melting and their luminescence properties

In this work, a novel recrystallization-melting method was used to prepare Eu2+ and Dy3+ co-doped Sr2MgSi2O7 translucency long afterglow glass-ceramics with complete crystal development. The synthesis mechanism is discussed by analyzing the detection results of X-ray diffraction, scanning electron microscopy, phosphorescence spectra, and afterglow attenuation curves. The effect of different firing temperatures and crystallization time on the crystalline phase content, crystal size, and luminescence properties of the Sr2MgSi2O7:Eu2+, Dy3+ glass-ceramics samples were examined. The results show that, as compared with the traditional melt crystallization method or the two-step method, the recrystallization–melting method is able to form some Sr2MgSi2O7:Eu2+, Dy3+ crystals first under a temperature that is lower than that of the glass transition. With increasing firing temperature and crystallization time, crystal growth and recrystallization reached an equilibrium state, accompanied by the generation of liquid glassy phases. It is found that the afterglow properties are proportional to the crystalline phase content and crystal size, with the latter having a more significant effect. Under the condition of firing at 1050 °C for 10 h, tetragonal Sr2MgSi2O7 crystals with a maximum size of 20 μm were successfully synthesized for the first time. These crystals exhibited high integrity and optimal afterglow performance, with a duration close to 2 h. The recrystallization-melting method suits industrial production on large scales, and the firing temperature is evidently lowered, which effectively reduces the energy consumption of the synthesis process and significantly improves the long afterglow performance.

Enhanced thermal stability and luminous properties of Dy3+/Tm3+/Eu3+ doped glass ceramics containing Sr4Bi(PO4)3O crystalline phases based on back energy transfer

White light emitting and optical temperature sensing materials with high thermal stability have broad market development prospects. The use of substrates with excellent thermal stability is a common idea to improve thermal stability, while the modulation of dopants to enhance thermal stability has been less studied. Therefore, in this work, Tm3+/Dy3+/Eu3+ doped transparent glass ceramics containing Sr4Bi(PO4)3O crystalline-phase were prepared by melt-crystallization method to achieve warm white light emission and optical temperature sensing with good thermal stability. Since the Tm3+-Dy3+ doped samples can only achieve cold white light emission, warm white light emission is obtained by adding Eu3+, which can emit red light. The application scenario of the material is expanded. The luminous intensities of Tm3+, Dy3+, and Eu3+ were 109.4 %, 89.1 %, and 70.7 % of those at room temperature, at 473 K. The increase in the emission intensity of Tm3+ was explained by the presence of back energy transfer (BET) from Dy3+ and Eu3+ to Tm3+. The chromaticity shift (Δε) of the samples was 2.43 × 10−4 and the luminescent colour was stable. The absolute sensitivity of the material can reach 0.69 K−1 at 473 K, and the relative sensitivity of the material can reach 1.60 % K−1 at 293 K. This work provides new ideas for the study of improving the thermal stability of materials.

Doping of n-type Bi2Se3 single crystal with Fe, Ru, Os, and Mo

Doping is one of the most suitable methods for tuning the electronic properties of topological insulators and a promising approach for band gap opening in surface states. In this study, we developed a reliable method for preparing high-quality single crystal substrates comprising Bi2Se3 doped with VIIIB and VIB column elements. We combined experimental photoelectron spectroscopy (X-ray photoelectron spectroscopy, angle resolved photoelectron emission spectroscopy, and ultraviolet photoelectron spectroscopy) and theoretical (ab initio) methods to analyze the electronic properties and chemical states of atoms in the substitutional position and native defects in the topological insulator, which can be achieved using the free melt crystallization method for sample growth. The relationship between the position of the Dirac cone and valence band maximum was explored and discussed.

Ionic thermoelectric effect in Cu2-δSe during phase transition

The ionic Seebeck coefficient was studied in copper selenide with Cu1.99Se, Cu1.95Se and Cu1.8Se stoichiometry which was synthesized with a melt crystallization method. To measure the ionic Seebeck coefficient of copper ions, 0.15C6H12N4CH3I + 0.85CuI solid-state electrolyte was prepared. Electrolyte layers were pressed with copper selenide powder into a sandwich-like structure. At the temperature of 410 K, the materials have ionic Seebeck coefficient values close to each other, about 1100 μV/K. In the case of β-phase structure (Cu1.8Se material), changes in the measured Seebeck coefficient were observed—with decreasing temperature, the ionic thermopower firstly increased reaching about 1230 μV/K and then decreased to 950 μV/K at 355 K. In the Cu1.99Se material, a phase transition to the α-phase was observed during cooling. The ionic Seebeck coefficient values gradually increased from 1030 to 1220 μV/K at 370 K, when the material is in the low-temperature phase. The measured difference between the ionic thermopower of the two phases well matches calculations based on the entropy of the transition (presence part of the Seebeck coefficient) and different activation energies of ionic transport (transport part).Graphical abstract

Constructing Tb3+→Mn2+ energy transfer to realize tunable luminescence and optical temperature measurement in glass-ceramics containing Y2Sn2O7

By using the melt crystallization method, Tb4O7−MnO2 co-doped glass-ceramics containing Y2Sn2O7 were synthesized. The heat treatment for glass-ceramics was determined to be 700 °C/1.5 h using differential scanning calorimetry analysis, X-ray diffraction, scanning electron microscopy, and light transmittance curves. FTIR spectroscopy further confirmed the precipitation of the Y2Sn2O7. Although MnO2 was used as the Mn source in this experiment, the glass-ceramic showed the luminescent properties of Mn2+. The emission spectra and fluorescence decay curves of Tb4O7−MnO2 co-doped glass-ceramics demonstrate the energy transfer phenomenon of Tb3+→Mn2+. When the doping concentration of MnO2 increases, the glass-ceramics can realize tunable luminescence from green light to yellow light to orange light. At 473 K, the luminescence intensity of Tb3+ and Mn2+ were 84.3% and 33.0% of those at room temperature. In terms of absolute and relative sensitivity, the maximum values for glass-ceramics were 1.18 × 10−2 K−1 and 1.52% K−1. The minimum temperature resolution is 0.05 K at 298 K. It is demonstrated that the prepared Tb4O7−MnO2 co-doped glass-ceramics containing Y2Sn2O7 have a promising application in the field of optical temperature measurement.

Glutaric acid purification by coupled solution crystallization and melt crystallization

The mixed dibasic acids (DBA) is a by-product during adipic acid (ADA) production by oxidation of cyclohexanol or cyclohexanone, which contains large amount of glutaric acid (GA) with ADA and succinic acid (SA). In this work, we have explored the feasibility of the coupled solution crystallization and melt crystallization for the purification of GA. To obtain fundamental thermodynamic properties for the process design, the gravimetric method was used to measure the solubility of the three dibasic acids in water from 293.15 K to 345.15 K at atmospheric pressure. The results showed that GA was the most soluble component while all solubility increased with increasing temperature. Therefore, it is reasonable to concentrate GA in the liquid phase by cooling crystallization. Similarly, the ternary solid-liquid melt equilibrium phase diagram was constructed based on the experimental data of the three binary subsystems (GA-ADA, GA-SA, ADA-SA). It was found that the concentrated GA after solvent evaporation could be purified by melt crystallization efficiently. Thus a coupled solution crystallization and melt crystallization process was designed. With the operated operating parameters, the purity of GA could reach 99.06% by secondary melt crystallization. Overall, the coupled solution crystallization and melt crystallization method to separate DBA has proven to be effective.

Structure, luminescence and thermal stability of Dy2O3–Eu2O3 co-doped transparent glass-ceramics containing Y2Sn2O7 crystal

A new transparent glass-ceramic containing Y2Sn2O7 crystal was synthesized utilizing the melt crystallization method. By using XRD, SEM, and DSC curves to identify the phase structure of the samples and observe their microscopic morphology, the optimal heat treatment conditions for the samples were determined to be 710 °C/2 h. Using the fluorescence probe characteristics of Eu3+, the different microstructures of precursor glasses and glass-ceramics were explored. The emission spectra of Dy2O3–Eu2O3 co-doped glass-ceramic samples showed three distinct emission peaks at 482 nm (Dy3+: 4F9/2 → 6H15/2), 575 nm (Dy3+: 4F9/2 → 6H13/2) and 614 nm (Eu3+: 5D0→7F2), while the emission spectra demonstrated the existence of energy transfer of Dy3+→Eu3+. Warm white light with low color temperature may be obtained by Dy2O3–Eu2O3 co-doped glass-ceramic samples, depending on the chromaticity coordinates and color temperature. The emission spectra of 0.4%Dy2O3-0.7%Eu2O3 co-doped glass-ceramic samples in the temperature range of 298 K–473 K show that at 423 K, the emission intensity at 482 nm, 575 nm, and 614 nm can still reach 71.5%, 78.8%, and 80.0% of the room temperature. We calculated the activation energy as 0.293 eV, and the color shift at 423 K was 7.3 × 10−3. The findings demonstrate the exceptional thermal stability of transparent glass-ceramics containing Y2Sn2O7 crystal and their prospective use in the manufacture of W-LEDs.

Preparation and luminescence of Dy3+/Tm3+ co-doped Ca3NbGa3Si2O14 glass-ceramics for w-LED

In this work, a series of Dy3+ and Dy3+/Tm3+ ion activated Ca3NbGa3Si2O14 glass-ceramics were prepared by traditional melt crystallization method, and report on the structural, optical, and energy transfer (ET)-based photoluminescence (PL) properties of glass-ceramics co-doped Dy3+/Tm3+. The preparation of glass-ceramics was studied by DTA, XRD, SEM, and UV–vis photometer technology, phase composition, transmittance, optimum heat treatment conditions, and luminescence properties. The best heat treatment procedure for obtaining transparent and well-formed glass-ceramics is crystallization at 820 °C for 5 h. The spectra excited by Tm3+ and Dy3+ have intersections at 352 nm and 365 nm, which means that CNGS: Dy3+/Tm3+ can be effectively excited by 352 nm and 365 nm ultraviolet light. Under the excitation of 352 nm ultraviolet light, four main emission peaks corresponding to 1D2 →3F4, 4F9/2 → 6H15/2, 4F9/2 → 6H13/2, 4F9/2 → 6H11/2 were found at 456 nm, 484 nm, 577 nm, and 663 nm, respectively. When the optimal concentration (4 at.%) of Dy3+ is Co-doped with a different amount of Tm3+, the luminous color can be adjusted by adjusting the doping amount of Tm3+ and changing the excitation wavelength. There is an overlapping region between the emission spectrum of Tm3+ doped glass and the excitation spectrum of Dy3+ doped glass, which indicates that there is energy transfer between Tm3+ and Dy3+. In addition, CNGS: Dy3+/Tm3+ CIE coordinates show that the color coordinates (0.3324, 0.3352) when y = 0.02 under 365 nm excitation are closest to the standard white light (0.333, 0.333), indicating that this glass has potential applications in WLED devices.

Eu3+ doped K2O-B2O3-Al2O3-SiO2 glass ceramics containing KAlSiO4 crystalline phase: Realizing red emission and high thermal stability

Eu3+ doped K2O-B2O3-Al2O3-SiO2 glass ceramics containing KAlSiO4 crystallite were synthesized by melt crystallization method. Differential scanning calorimetry (DSC) analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to identify the optimal heat treatment conditions for glass ceramics, which were 560 °C/90 min. The light transmittance of the glass ceramics can reach up to 75% in the visible light range. The luminescence properties of glass ceramics were studied by fluorescence spectra, and the optimal doping concentration of Eu3+ was determined to be 0.7%. At this concentration, the fluorescence lifetime is 1.65 ms, the chromaticity coordinate (CIE) is (0.583, 0.4048). The luminescent properties of glass ceramics have high stability under the change of temperature (300–460 K). Eu3+ doped K2O-B2O3-Al2O3-SiO2 based glass ceramics have potential applications in solid-state lighting, red lasers.

Optical properties of near infrared persistent phosphor CaZnGe2O6: Cr3+, M3+ (M3+ = B3+; Al3+; Ga3+)

Persistent luminescence (PersL) is a phenomenon when a material continues to emit light for a period of time, usually several minutes or hours after the removal of the excitation source. Although it is possible to find several hundred different materials suitable for the observation of PersL in the visible part of the spectrum, only a handful of them is applied to obtain phosphors for near infrared (NIR) emission. In the course of this work, CaZnGe2O6: Cr3+, M3+ (M3+ = B3+; Al3+; Ga3+) materials have been synthesized by a melt crystallization method. Photoluminescence (PL) and subsequent PersL of chromium ions in the NIR spectral region, as well as visible PL and PersL of the host material, have been observed. After irradiation with ultraviolet (UV) radiation, a broad NIR PersL band with a maximum around 790 nm and an afterglow time over 1 h has been detected. The addition of B3+; Al3+; Ga3+ increases the overall intensity and duration of PersL. The analysis of PersL decay curves and glow curves of thermally stimulated luminescence (TSL) show multiple trap centres involved in the generation of PersL.

Enhancing the orange luminescence behavior of the Li+ co-doped Ca2Ti2O6: Sm3+transparent glass-ceramic

The Sm3+ doped transparent glass-ceramics were prepared by the melt crystallization method. Using the device of X-ray diffraction (XRD) can confirm Ca2Ti2O6 nanocrystals were formed among the precursor glass matrix. Under the optimum heat treatment condition (680 °C/90 min), the average grain size in the glass-ceramic is about 103 nm, and the light transmittance in the visible region can reach 78%. Under 402 nm excitation, the emission spectra show strong emission peaks at 564 nm, 600 nm and 647 nm, corresponding to the 4G5/2→6HJ (J = 5/2, 7/2, 9/2) characteristic transitions of Sm3+. The optimal doping concentration of Sm3+ is 0.5%, and the concentration quenching caused by exchange interaction will occur if it exceeds this value. The introduction of Li+ into glass-ceramics will not change the crystal phase and can enhance the luminescent intensity. The chromaticity coordinates of 4%Li+-0.5%Sm3+ co-doped glass-ceramic are located in orange region (0.5506, 0.4456), and the color purity can reach 95.4%. The results show that the glass-ceramics have potential applications in solid-state color rendering.

Stereocomplex and individual crystallization behavior of symmetric or enantiomeric substituted Poly(lactic acid)s random copolymers with high crystallizabilities

Stereocomplex (SC) crystallization is reported for the first time for the enantiomeric blends of random copolymers of l-configured poly(l-2-hydroxybutanoic acid-co-l-2-hydroxy-3-methylbutanoic acid) [P(L-2HB-co-L-2H3MB)] (49/51) and d-configured poly(d-2-hydroxybutanoic acid-co-d-2-hydroxy-3-methylbutanoic acid) [P(D-2HB-co-D-2H3MB)] (47/53) with high individual crystallizabilities. Unblended l-configured P(L-2HB-co-L-2H3MB) and d-configured P(D-2HB-co-D-2H3MB) formed individual crystallites through purification, solvent evaporation, and melt crystallization. Three types of individual crystallites (provisionally named as α-, β-, and γ-forms) were observed in the unblended copolymers depending on the crystallization methods. SC crystallites were formed in the blends through solvent evaporation and melt crystallization method. All types of monomer units cocrystallized in the individual and SC crystallites. The melting and equilibrium-melting temperatures of SC crystallites in the blends were 192.5–203.7 °C and 205.2 °C, respectively, which were significantly higher than the melting temperatures of individual crystallites in the unblended copolymers (61.6–133.1 °C). The maximum radial growth rate of SC crystallites (13.5 μm min−1) was 10 and 27 times higher than those of individual crystallites of the unblended copolymers (1.4 and 0.5 μm min−1), indicating that SC crystallization increased the crystallization rate. SC crystallization proceeded via regimes II and III. The copolymer crystallizability, monomer cocrystallizability, and crystallization rate of P(L-2HB-co-L-2H3MB) (49/51) and P(D-2HB-co-D-2H3MB) (47/53) are compared with those reported for the series of symmetric or enantiomeric polymer blends of poly(l-lactic acid-co-l-2-hydroxybutanoic acid) (56/44) and poly(d-lactic acid-co-d-2-hydroxybutanoic acid) (52/48) with lowindividualcrystallizabilities and poly(l-lactic acid-co-l-2-hydroxy-3-methylbutanoic acid) (47/53) and poly(d-lactic acid-co-d-2-hydroxy-3-methylbutanoic acid) (47/53) with noindividualcrystallizability.

Tb3+/Eu3+ co-doped Al2O3–B2O3–SrO glass ceramics: Preparation, structure and luminescence properties

Al2O3–B2O3–SrO glass ceramics were manufactured by the melt crystallization method, Tb3+ and Eu3+ were doped and the luminescence properties were investigated. The experimental conditions for the optimal heat treatment of borate glass ceramics were determined by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscope (SEM). The luminescence spectra of glass ceramics were measured, the emission peaks at 489 nm and 544 nm belong to Tb3+, and at 590 nm and 614 nm belong to Eu3+, under the 377 nm excitation. The energy transfer from Tb3+ to Eu3+ was determined by the fluorescence attenuation curve of Tb3+, and the interaction between rare earth ions was determined by calculating the critical distance. Borate glass ceramics doped with Tb3+ and Eu3+ glow in the blue to orange range, when 1.2%Tb3+-1.2%Eu3+ doped glass ceramic samples are closest to the perfect white light, according to the CIE1931 chrominance coordinates. Borate glass ceramics doped with Tb3+/Eu3+ are suitable for LED and display devices.

Synthesis and up-conversion luminescence properties of Ho3+-Yb3+ co-doped glass ceramics containing Sr3Gd(PO4)3

Ho3+-Yb3+ co-doped transparent glass ceramics containing Sr3Gd(PO4)3 were successfully prepared by the melt crystallization method. The best condition of the thermal treatment was determined to be 780 °C/3 h by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscope (SEM). The transmittance of glass ceramic was approximately 81% in the visible region. From to the up-conversion emission spectra, the strong green emission (543 nm), weak red (654 nm) and blue emission (483 nm) due to the 5F4/5S2, 5F5, 5F3 → 5I8 transitions of Ho3+ can be observed. In addition, the optimum doping concentration of Ho2O3 and Yb2O3 was 0.3% and 0.8%, respectively. By comparing 0.3%Ho2O3-0.8%Yb2O3 co-doped with 0.3%Ho2O3 doped glass ceramic, the green and red up-conversion luminescence intensity were improved by about 33 times and 21 times, respectively. These results indicated that Ho3+-Yb3+ co-doped transparent glass ceramic containing Sr3Gd(PO4)3 have potential applications in the field of green up-conversion luminescence.

Luminescence properties of Eu3+ doped borate glass ceramics containing Al4B2O9

Borate glass ceramics doped with Eu3+ were prepared by the melt crystallization method. The crystalline phase Al4B2O9 in the glass-ceramics was determined by X-ray diffraction.. The optimal doping concentration of Eu3+ was obtained by the emission spectrum, and the color purity corresponding to the optimal doping concentration was calculated. Compared with glass samples, it is proved that glass ceramics have high luminescence intensity.

Preparation and luminescence of Dy3+ doped glass-ceramics containing ZnMoO4

Dy3+ doped ZnMoO4 glass-ceramics was prepared by traditional melt crystallization method. The crystalline phase, microscopic morphology, transmittance, the optimal heat treatment condition and luminescence properties of the samples were discussed. The emission peaks are located at 482 nm, 574 nm and 663 nm due to 4F9/2→6H15/2, 4F9/2→6H13/2 and 4F9/2→6H11/2 transitions of Dy3+ under 387 nm. When the doped concentration of Dy3+ exceeded 0.4%, it was proved that the multi-stage interaction between adjacent ions causes concentration quenching by calculating the critical distance between Dy3+. The chromaticity coordinate (CIE) showed the luminescence color of the samples in the white light region, indicating that Dy3+ doped glass-ceramics containing ZnMoO4 were expected to be applied in white-light emitting diode (w-LED).