High-temperature Solid-phase Method Research Articles

Experimental Optimization, Design Synthesis, and Up-Conversion Luminescence Properties of Y4GeO8: Er3+/Yb3+ Red Phosphors

The Er3+/Yb3+ co-doped Y4GeO8 crystal powders were successfully synthesized us-ing a high-temperature solid-phase method. The crystal structure of the obtained phosphors was confirmed to be pure Y4GeO8 through X-ray diffraction (XRD) analysis. A regression equation correlating Er3+/Yb3+ doping concentrations with luminescent intensity was estab-lished based on the optimized theoretical model derived from experimental design. The op-timal concentrations of Er3+ and Yb3+ under 980 nm laser excitation were determined as 7.41% and 21.34%, respectively, while under 1550 nm laser excitation, the concentrations were 2.66% and 17.42%, respectively. The fluorescence emission spectra of the up-conver-sion samples were measured, revealing intense green and red emissions with peaks at 542, 546, and 654 nm under 980 nm excitation, and peaks at 546, 557, and 663 nm under 1550 nm excitation. These peaks correspond to transitions from 2H11/2 to 4I15/2, 4S3/2 to 4I15/2, and 4F9/2 to 4I15/2 energy levels. The relationship between up-conversion luminescence and laser op-erating current for the optimal samples under 980 nm and 1550 nm was investigated, uncov-ering that up-conversion luminescence occurs through both two-photon and three-photon processes. A detailed analysis and discussion of the up-conversion luminescence mecha-nisms were conducted. Furthermore, the relationship between up-conversion fluorescence and temperature for the optimal samples was studied, revealing excellent temperature-sens-ing characteristics under 980 nm and 1550 nm laser excitations. The calculated illumination region coordinates for the optimal samples under 980 nm and 1550 nm wavelength excitations were (0.5558, 0.4362) and (0.5256, 0.4687), respectively. The research highlights the potential of rare-earth ion-doped up-conversion luminescent materials for diverse anti-coun-terfeiting applications. In particular, the Y4GeO8: Yb3+/Er3+ phosphors, incorporating a dual-excitation mechanism, enhance the security of anticounterfeiting strategies in multifaceted scenarios. The study underscores the promising developments in this field.

Evidence and Practical Applications of Site Occupancy Theory (SOT) of Eu3+ in Scheelite Compounds.

The determination of the site occupancy of activators in phosphors is essential for precise synthesis, understanding the relationship between their luminescence properties and crystal structure, and tailoring their properties by modifying the host composition. Herein, one simple method was proposed to help determine the sites at which the doping of rare earth ions or transition metal ions occupies in the host lattice through site occupancy theory (SOT) for ions doped into the matrix lattice. SOT was established based on the fact that doping ions preferentially occupy the sites with the lowest bonding energy deviations. In order to provide detailed experimental evidence to prove the feasibility of SOT, several scheelite-type compounds were successfully synthesized using a high-temperature solid-phase method. When Eu3+ ions occupy a similar surrounding environment site, the photoluminescence spectra of the activators Eu3+ are similar. Therefore, by comparing the intensity ratio of photoluminescence spectra and the mechanism of all transitions of KEu(WO4)2, KY(WO4)2:Eu3+, Na5Eu(WO4)4, and Na5Y(WO4)4:Eu3+, it was proved that SOT can successfully confirm the site occupation when doped ions enter the matrix lattice. SOT was further applied to the sites occupied by Eu3+ ion-doped LiAl(MoO4)2 and LiLu(MoO4)2.

Defect engineering build organic-inorganic composite electrolytes with stable electrochemical window and interface for all-solid-state lithium-ion batteries

In this study, Na1+xAlxTi2-x(PO4)3 (NATP) with oxygen vacancies was synthesized using a high-temperature solid-phase method. Then, NATP and polyacrylonitrile (PAN) were combined to form NATP-PAN composite solid-state electrolytes. X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses demonstrated the presence of oxygen defects in NATP. Al3+ doping created oxygen vacancies in NATP, which decreased the activation energy for Li+ ions transport; this increased the mobility of Li+ ions in the material, broadening the electrochemical window of the electrolyte. The Na1.3Al0.3Ti1.7(PO4)3-PAN solid-state electrolytes achieved an excellent ionic conductivity of 4.51 × 10−4 S cm−1 at 20 °C and a wide electrochemical stability window of 5.2 V (vs. Li+/Li). Na1.3Al0.3Ti1.7(PO4)3-PAN composite electrolyte was used to assemble a Li||Li symmetric half-cell, which exhibited good interface stability and an overpotential of approximately ±60 mV at a current density of 0.25 mA cm−2. Furthermore, Li׀Na1.3Al0.3Ti1.7(PO4)3-PAN׀LiFePO4 was assembled into an all-solid-state lithium metal battery, which exhibited excellent electrochemical performance, with the initial discharge capacity of 255.0 mA h g−1 at 0.1 C. After 100 cycles, the discharge capacity was maintained at 229.6 mA h g−1, and the capacity retention rate was 90.0 %. Increasing dopant concentration, the oxygen defect concentration is increasing, which plays a crucial role in the ionic conductivity as well as the interface stability.

Effect of ion occupancy and Li+ ion doping on luminescence characteristics of CaLaGaO4:Bi3+ blue phosphor

In recent years, the application of Bi3+ ions doped luminescent materials in the field of optoelectronics has attracted wide attention. In this paper, CaLaGaO4:xBi3+(x = 0.005, 0.0075, 0.01, 0.0125, 0.015, 0.02, 0.025mol) blue phosphors were synthesized by high temperature solid phase method. The theoretical and experimental bandgap values after Bi3+ ions doping is reduced, indicate that electrons can be transferred from valence band to conduction band better after Bi3+ ions doping, which increases the carrier concentration and improves the luminous efficiency. In addition, due to the doping of Li+ ions under 365nm excitation, the emission intensity is increased by 2.5 times, shows high brightness blue light, with excellent thermal stability (423K/303K = 83%), quantum efficiency is 56%, and CaLaGaO4:0.01Bi3+, 0.008Li+ phosphor was mixed with (Ba,Sr)2SiO4:Eu2+ commercial green phosphor and (Ca,Sr)AlSiN3:Eu2+ red phosphor in a certain proportion. The WLED combined with 365nm chip has a high color rendering index Ra = 90.2. Relevant color temperature CCT = 5502K.

Preparation and sensing performance study in ultra-wide temperature range of K3LuF6:Er3+,Yb3+ up-converting luminescent materials with cryolite structure

Cryolite-type materials have advantages of low phonon energy, easy rare-earth ion doping, and stable physicochemical properties, and they are considered ideal matrices for up-converting luminescent materials. In this paper, a series of K3LuF6:Er3+,Yb3+ up-converting materials with cryolite structure were prepared for the first time by high-temperature solid-phase method. The compositions, structures and luminescent properties were systematically characterized by X-ray powder diffractometry (XRD), field emission scanning electron microscopy (SEM) and fluorescence spectroscopy (PL). Under 980 nm excitation, the sample emission spectra mainly consisted of green and red emission bands with peaks at 525, 546 and 662 nm, corresponding to the 2H11/2-4I15/2, 4S3/2-4I15/2 and 4F9/2-4I15/2 electron transitions of Er3+, respectively. In addition, the temperature sensing characteristics of two thermally coupled energy levels (2H2/11 and 4S3/2) were studied based on the fluorescence intensity ratio (FIR) technique in the range of 79–579 K. All the results show that K3LuF6:Er3+/Yb3+ up-converting luminescent materials have excellent temperature sensing performance in the ultra-wide temperature range and have broad application prospects in the field of temperature sensing.

Unraveling two yellow fluorescence emission mechanisms and color-changing afterglow characteristics of Dy-doped Mg2SnO4 luminescent materials

In this work, Dy ion doped Mg2SnO4 (Mg2SnO4:Dy3+) with monochromatic yellow fluorescence and color-changing long afterglow properties are prepared by the high-temperature solid-phase method. Mg2SnO4:Dy3+ shows the best luminescence performance under the preparation conditions of 1550 °C and 0.02 Dy3+ concentration. The samples are able to achieve yellow fluorescence emission (λem = 575 nm) under 350 nm and 291 nm excitation, and the emission intensity of the samples under 350 nm excitation is much higher than that of 291 nm excitation. Under 254 nm excitation, the sample not only emits bright white fluorescence but also has the ability of obvious afterglow after excitation. Moreover, the afterglow also has the color change function of transition from bright white to yellow. The luminescence mechanism study shows that Mg2SnO4:Dy3+ contains two emission centers, Dy3+ and lattice defects. Combining the results of spectroscopic measurements with the Dy3+ energy level distribution data, two different fluorescence emission processes under 291 and 350 nm excitation as well as the afterglow discoloration mechanism due to 254 nm excitation are discussed in detail.

Bi3+/Mn4+ co-doped Y2MgTiO6 dual-emitting phosphors for plant growth lighting and temperature sensor

Novel Bi3+/Mn4+ co-doped Y2MgTiO6 dual-emitting phosphors were synthesized using a high-temperature solid-phase method. The crystal structure and luminescence properties of phosphors were systematically investigated by experimental characterization and theoretical calculation. Under excitation at 375 nm, Y2MgTiO6:Bi3+, Mn4+ phosphors exhibit two emission bands located at 410 nm and 696 nm (blue and red), which can well be matched with the absorption bands of chlorophylls a, b and phytochrome. The Y2MgTiO6: Bi3+, Mn4+ luminescence remains at 66.2 % intensity at 423 K and quantum yield is 52.06 %. Optical temperature properties of Y2MgTiO6:Bi3+, Mn4+ were investigated using fluorescence intensity ratio (FIR) analysis and were found to reach a maximum relative sensitivity of 2.93 % K−1 at 498 K. The study suggests that this material could be a potential option for indoor plant culture and optical temperature sensing.

Luminescence and energy transfer properties of color-tunable Dy3+, Eu3+ co-activated NaGdSiO4 phosphor for WLED with great thermo-stability.

A series of NaGd1-x-ySiO4: y Dy3+ - x Eu3+ phosphors were synthesized by a high-temperature solid-phase method. The optimal doping ion concentration of Dy3+ ions for this phosphor was determined to be 1% from the emission spectra. The energy transfer between Dy3+ and Eu3+ ions at 351 nm was investigated by photoluminescence spectra and fluorescence decay curves. At the excitation wavelengths of 275 nm, 351 nm, 366 nm, and 394 nm, a change from yellow to white to red light can be realized by adjusting the doping concentration of Eu/Dy ions. Particularly, by testing the temperature-dependent fluorescence spectrum of the phosphor, it can be found that the luminous intensity of the phosphor is as high as 96% when 394 nm excitation is employed at 413 K. It was the maximum at this temperature comparing with other phosphors as far as we know. The color coordinate values show that the NaGd1-x-ySiO4: x Dy3+ - y Eu3+ phosphors are very close to the white light color coordinates (x = 0.33, y = 0.33) under 351 nm excitation. Meanwhile, the correlated color temperature is between 5062 - 7104 K. These results indicate that this phosphor is a promising candidate for high-quality WLED.

Preparation and properties of cordierite-based multi-phase composite far-infrared emission ceramics by fine-grained tailings

In this paper, cordierite ceramics with high far-infrared emission properties are synthesized by a high-temperature solid-phase method using molybdenum tailings and vanadium-titanium magnetite tailings. The microstructure, physical properties and far-infrared emission mechanism of ceramics are investigated. The results show that the ceramics synthesized with 10 wt% molybdenum tailings and 30 wt% vanadium-titanium magnetite tailings have a flexural strength of 67 MPa, a bulk density of 2.531 g/cm3 and a maximum far-infrared emissivity of 0.958 when the sintering temperature is 1200 °C. The crystal phase of the ceramic are 21.4 % cordierite and 58.7 % magnesia-alumina spinel. In the sintering process, the Fe3+ in vanadium-titanium magnetite tailings doped into the cordierite to substitute the Mg2+, which has the similar ionic radius with Fe3+, to form a substitutional solute. Ionic substitution causes the lattice parameters of cordierite larger, reducing the symmetry of the lattice vibrations and leading to lattice distortion. In addition, the composition of a large amount of magnesia-aluminum spinel is attributed to the far-infrared emission properties of ceramics.

A Study on the Microstructure Regulation Effect of Niobium Doping on LiNi0.88Co0.05Mn0.07O2 and the Electrochemical Performance of the Composite Material under High Voltage.

High-nickel ternary materials are currently the most promising lithium battery cathode materials due to their development and application potential. Nevertheless, these materials encounter challenges like cation mixing, lattice oxygen loss, interfacial reactions, and microcracks. These issues are exacerbated at high voltages, compromising their cyclic stability and safety. In this study, we successfully prepared Nb5+-doped high-nickel ternary cathode materials via a high-temperature solid-phase method. We investigated the impact of Nb5+ doping on the microstructure and electrochemical properties of LiNi0.88Co0.05Mn0.07O2 ternary cathode materials by varying the amount of Nb2O5 added. The experimental results suggest that Nb5+ doping does not alter the crystal structure but modifies the particle morphology, yielding radially distributed, elongated, rod-like structures. This morphology effectively mitigates the anisotropic volume changes during cycling, thereby bolstering the material's cyclic stability. The material exhibits a discharge capacity of 224.4 mAh g-1 at 0.1C and 200.3 mAh g-1 at 1C, within a voltage range of 2.7 V-4.5 V. Following 100 cycles at 1C, the capacity retention rate maintains a high level of 92.9%, highlighting the material's remarkable capacity retention and cyclic stability under high-voltage conditions. The enhancement of cyclic stability is primarily due to the synergistic effects caused by Nb5+ doping. Nb5+ modifies the particle morphology, thereby mitigating the formation of microcracks. The formation of high-energy Nb-O bonds prevents oxygen precipitation at high voltages, minimizes the irreversibility of the H2-H3 phase transition, and thereby enhances the stability of the composite material at high voltages.

Medium- and High-Entropy Rare Earth Hexaborides with Enhanced Solar Energy Absorption and Infrared Emissivity.

The development of a new generation of solid particle solar receivers (SPSRs) with high solar absorptivity (0.28-2.5 μm) and high infrared emissivity (1-22 μm) is crucial and has attracted much attention for the attainment of the goals of "peak carbon" and "carbon neutrality". To achieve the modulation of infrared emission and solar absorptivity, two types of medium- and high-entropy rare-earth hexaboride (ME/HEREB6) ceramics, (La0.25Sm0.25Ce0.25Eu0.25)B6 (MEREB6) and (La0.2Sm0.2Ce0.2Eu0.2Ba0.2)B6 (HEREB6), with severe lattice distortions were synthesized using a high-temperature solid-phase method. Compared to single-phase lanthanum hexaboride (LaB6), HEREB6 ceramics show an increase in solar absorptivity from 54.06% to 87.75% in the range of 0.28-2.5 μm and an increase in infrared emissivity from 76.19% to 89.96% in the 1-22 μm wavelength range. On the one hand, decreasing the free electron concentration and the plasma frequency reduces the reflection and ultimately increases the solar absorptivity. On the other hand, the lattice distortion induces changes in the B-B bond length, leading to significant changes in the Raman scattering spectrum, which affects the damping constant and ultimately increases the infrared emissivity. In conclusion, the multicomponent design can effectively improve the solar energy absorption and heat transfer capacity of ME/HEREB6, thus providing a new avenue for the development of solid particles.

Titanium-based lithium ion sieve adsorbent H2TiO3 with enhanced Li+ adsorption properties by magnetic Fe doping

The titanium-based lithium ion sieve adsorbent H2TiO3 (HTO), known for its structural stability and high adsorption capacity, emerges as a highly promising material. Nonetheless, its precursor, the Li2TiO3 powder (LTO), synthesized via the high-temperature solid-phase method, tends to agglomerate and poses challenges in separation. This agglomeration compromises the adsorption sites and, consequently, its adsorption capacity. To counter this, we employed a strategy of doping LTO with magnetic Fe3O4 nanoparticles as a Fe source, aiming to mitigate the agglomeration issue. Subsequently, Fe-doped H2TiO3 (HFTO) was obtained by acid washing and used to adsorb lithium ions from an aqueous solution. Experimental results revealed that HFTO's equilibrium adsorption capacity for lithium in LiCl solution peaked at 34.27 mg/g. Moreover, even after five cycles of adsorption–desorption, HFTO maintained an adsorption capacity exceeding 32.00 mg/g. Investigations into HFTO's adsorption mechanism, utilizing Raman spectroscopy, FT-IR, and XPS, uncovered that the adsorption of Li+ by HFTO occurs through the dissociation of O–H bonds and the subsequent formation of O-Li bonds.

Constructing Enhanced Composite Solid-State Electrolytes with Sb/Nb Co-Doped LLZO and PVDF-HFP

Composite solid-state electrolytes are viewed as promising materials for solid-state lithium-ion batteries due to their combined advantages of inorganic solid-state electrolytes and solid-state polymer electrolytes. In this study, the solid electrolytes Li6.7−xLa3Zr1.7−xSb0.3NbxO12 (LLZSNO) with Sb and Nb co-doping were prepared by a high-temperature solid-phase method. Results indicate that Sb/Nb co-doping causes lattice deformation in LLZO and increases the lithium vacancy concentration and conductivity of LLZO. Then, with the co-doped LLZSNO as an inorganic filler, a composite solid electrolyte of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was prepared with a casting method. The obtained composite solid electrolyte exhibits a high ionic conductivity of 1.76 × 10−4 S/cm at room temperature, a wide electrochemical stable window of 5.2 V, and a lithium-ion transfer number of 0.32. The Li|LiFePO4 coin battery with the composite solid electrolyte shows a high specific capacity of 161.2 mAh/g and a Coulombic efficiency close to 100% at 1 C. In addition, the symmetrical lithium battery Li|Li with the composite electrolyte could cycle stably for about 1500 h without failure at room temperature.

Preparation of BaAl2-xGaxSi2O8:Ce3+, M+ (Li, Na, K) blue-cyan phosphors based on charge compensation and cation substitution strategies and luminescence performance study

Highly efficient blue-cyan phosphors can fill the cyan gap in conventional white light-emitting diode (LED) devices to improve the spectral continuity while effectively increasing the white LED colour rendering index (Ra). In this study, Ba0·94Al2-xGaxSi2O8:0.06Ce3+, M+ (Li, Na, K, x = 0–0.8) blue-cyan phosphors with a feldspar structure were prepared by a high-temperature solid-phase method using charge compensation and cation substitution strategies. The barium (Ba) vacancy due to the charge-imbalance substitution of Ce3+ is compensated by the different charge compensators Li+, Na+, and K+. The charge compensators affect the luminescence performance of the samples, with the K+-compensated samples showing the greatest enhancement, with intensities up to 1.8 times that of the uncompensated samples. The cation substitution strategy using Ga3+ to partially replace Al3+ further improves the luminescence performance of the Ba0·94Al2Si2O8:0.06Ce3+, 0.04 K+ sample, and the excitation band is also improved. In this case, the luminescence intensity of the Ba0·94Al2Si2O8:0.06Ce3+ luminescent material is increased by a factor of 6, and a broadband blue-cyan phosphor with a full-width at half-maximum of 118 nm containing blue, cyan and green is obtained. The co-doping of charge compensators and partial cation substitution improved the luminescence performance of phosphors. The representative sample Ba0·94Al1.6Ga0.4Si2O8:0.06Ce3+, 0.04 K+ has a luminescence intensity at a temperature of 150 °C that is 83.2% of that at room temperature and good thermal stability. The combination of 365 nm near-ultraviolet (NUV) LED chips with Ba0·94Al1.6Ga0.4Si2O8:0.06Ce3+, 0.04 K+ and the commercial red powder (Ca, Sr)AlSiN3:Eu2+ yields a white LED device with an Ra of up to 93 and a correlated colour temperature (CCT) of 4825 K. These results show that the blue-cyan phosphor complements the cyan component while simplifying the manufacturing process of white LEDs.

Strategy of Charge Compensation for High-Performance Ni2+-Activated MgAl2O4 Spinel Near-Infrared Phosphor Synthesis via the Sol-Gel Combustion Method.

Near-infrared (NIR) phosphor conversion light-emitting diodes (pc-LEDs) have great application potential as NIR light sources in many fields such as food analysis, night vision illumination, and bioimaging for noninvasive medical diagnosis. In general, phosphors synthesized by a high-temperature solid-phase method have large particle sizes and have to be processed to fine powders by a grinding process, which may introduce surface defects and lower the luminous efficiency. Here, we report a sol-gel sintering method with ammonium nitrate and citric acid as the sacrificing agents to synthesize high purity, nanosized (less than 50 nm) Zr4+/Ni2+ codoped MgAl2O4 spinel NIR phosphors, in which MgAl2O4 spinel is the matrix, Ni2+ is the luminous center, and Zr4+ acts as the charge compensator. We systematically characterized the crystal structures and NIR luminescence properties of the Ni2+-doped MgAl2O4 and the Zr4+/Ni2+ codoped MgAl2O4. Under 390 nm light excitation, the emission spectrum of the Ni2+-doped MgAl2O4 phosphor covers 900-1600 nm, the half-peak width is 251 nm, and the peak position is located at 1230 nm. We demonstrated that by incorporating small amounts of Zr4+ as the charge compensator, the NIR emission intensity of the Zr4+/Ni2+ codoped MgAl2O4 nanosized phosphor was doubled over that of the Ni2+-doped MgAl2O4 phosphor. The optimal content of the charge compensator was 2 mol %. More importantly, the inclusion of Zr4+ led to a NIR phosphor with improved thermal stability in luminous properties, and the luminous intensity measured at 100 °C was 33.83% of that measured at room temperature (20 °C). This study demonstrates that NIR phosphor nanomaterials with high-purity and enhanced optical properties can be designed and synthesized through the charge compensation strategy by a sol-gel sintering method.

Electrical conductivity, luminescence, and deep acceptor levels in β-Ga2O3-In2O3 polycrystalline solid solution doped with Zr4+ or Ca2+ ions

Photoluminescence, luminescence excitation spectra, and electrical conductivity of β-Ga2O3-In2O3 solid solutions were studied. For this purpose, polycrystalline samples of unintentionally doped (UID) and doped with Ca or Zr β-Ga2O3-In2O3 solid solution with 20% In were synthesized and characterized. All samples were obtained by the high-temperature solid-phase method from appropriate oxides at 1300 °C at low and high oxygen partial pressure. It was established that UID and doped with Ca2+ or Zr4+ samples synthesized in an oxygen atmosphere were highly resistive, while the samples synthesized in an argon atmosphere had high conductivity. The conductivity was the lowest in the samples doped with Ca2+ and was 10−13 Ω−1 cm−1, while in the samples doped with Zr4+, the electrical conductivity was the highest and reached 10−3 Ω−1 cm−1. The broadband luminescence of β-Ga2O3-In2O3 solid solution is a superposition of three elementary bands with maxima in the violet 3.08 eV, blue 2.73 eV, and green 2.45 eV regions of the spectrum. Doping with Ca2+ or Zr4+ impurities and varying the synthesis atmosphere led mainly to a redistribution of intensities between the elementary luminescence bands. The luminescence arises from the radiative recombination of charge carriers through donor–acceptor pairs and self-localized holes. Donors and acceptors are formed by native defects such as (Gai, VGa, VGaVo) or doping impurities (Zr4+, Ca2+). Unlike the luminescence spectra, the luminescence excitation spectra change significantly when the synthesis conditions vary or when doping with divalent impurities. The excitation band at 4.46 eV is due to electron transitions from the VGa or VGaVO acceptor levels to the conduction band. Electron transitions from acceptor levels of Ca2+ impurities are manifested in the intense excitation band at 4.1 eV.

Upconversion Luminescence Properties and Temperature Sensing Characteristics of Tm3+, Yb3+-codoped SrAl2Si2O8 Phosphors with High Thermometric Sensitivities

In this paper, a SrAl2Si2O8:Tm3+,Yb3+ upconversion (UC) phosphor was prepared with a high-temperature solid-phase method, and proved that the strontium feldspar structure was an excellent UC matrix. The Tm3+ were shown to have a maximum relative thermometric sensitivity (Sr) of 1.67% K−1 at 298 K and a maximum absolute thermometric sensitivity (Sa) of 1.34% K−1 at 573 K. The non-thermally coupled energy level corresponded to the maximum relative thermometry sensitivity (Sr) of 2.4% K−1 at 298 K and a maximum absolute sensitivity (Sa) of 13% K−1 at 423 K. The use of the fluorescence intensity ratio of the nonthermally coupled energy levels of Tm3+ for temperature measurements improved the temperature measurement sensitivity of the same material. These results indicated that the phosphor has good temperature sensing performance with a wide sensing range and good stability and has potential thermometry applications in the first biological window.

Layered Chalcogenide Scintillators Enabled by Reversible Hydrous-Induced Phase Transformation for High-Resolution X-ray Imaging.

Scintillation materials have been widely used in various fields, such as medical diagnosis and industrial detection. Chalcogenides have the potential to become a new generation of high-performance scintillation materials due to their high effective atomic number and good resistance to radiation damage. However, research on their application in radiation detection is currently very scarce. Herein, single crystals of rare earth ion-doped ternary chalcogenides NaGaS2/Eu were grown by a high-temperature solid-phase method. It exhibits unique characteristics of structure transformation by absorbing water molecules from the air. To maintain the anhydrous phase of the material, we have used a strategy of organic-inorganic composites of epoxy resin and NaGaS2/Eu to prepare devices for radiation detection and discuss the irradiation luminescence properties of the two phases. The anhydrous phase of NaGaS2/Eu demonstrates excellent sensitivity to X-rays, with a low detection limit of 250 nGy s-1, which is approximately 1/22 of the medical imaging dose. Additionally, composite flexible films were prepared, which exhibited excellent performance in X-ray imaging. These films enable clear observation of a wide range of objects with a high spatial resolution of up to 13.2 line pairs per millimeter (lp mm-1), indicating that chalcogenide holds promising prospects in the realm of X-ray imaging applications.

Effects of Na+, Ga3+ introduction on the luminescence properties of LiAl4O6F: Mn4+ red fluorescent materials

LiAl4O6F (LAOF): Mn4+, Na+, Ga3+ red fluorescent materials were prepared by high temperature solid phase method. The properties of LAOF: Mn4+, Na+, Ga3+ phosphors were characterized by X-ray diffraction (XRD), photoluminescence (PL) spectra, variable temperature spectroscopy, scanning electron microscopy (SEM) and other tests. Under the excitation of 450 nm light, an intense red emission peak was observed around 662 nm, corresponding to the 2Eg→4A2g transition of Mn4+. Compared with Mn4+ single doping, the introduction of Na+, Ga3+ greatly improves the luminescence intensity of LAOF. The photoluminescence quantum yield of the optimal LAOF: 0.2%Mn4+, 0.2%Na+, 3%Ga3+ phosphor was measured to be 41.6%. The prepared sample have excellent thermal and water stability. Meanwhile, the w-LED device with a beneficial luminescence efficiency (LE = 331.7 lm W−1), exhibited good CRI and CCT values. These results indicate that LAOF: Mn4+, Na+, Ga3+ phosphors have potential application prospects as a red component in the field of lighting display.

Preparation of Er3+, Ho3+, Yb3+-doped Bi2WO6 upconversion luminescent materials and their temperature sensing properties

A high-temperature solid-phase method was used to prepare codoped Bi2WO6 upconversion luminescent materials with different concentrations of Er3+, Ho3+, and Yb3+. The microstructure, upconversion luminescence and temperature sensing properties of the synthesized powders were analyzed. X-ray diffraction (XRD) patterns showed that the doping of Er3+, Ho3+, and Yb3+ did not affect the orthorhombic crystal structure of the Bi2WO6 matrix material. As the calcination temperature increased from 800 °C to 1000 °C for 3h, the average particle sizes of the 1% Er3+, 1% Ho3+, 1% Yb3+: Bi2WO6 samples decreased, and the luminescence weakened. Scanning electron microscopy (SEM) images showed that the morphology of the sample for 1% Er3+, 1% Ho3+, 1% Yb3+: Bi2WO6 with calcination at 800 °C was nearly spherical, with particle sizes ranging from 1 to 5 μm and some agglomeration. SEM mapping showed that the elements were more uniformly distributed on the surfaces of the sample particles, and energy-dispersive X-ray spectroscopy (EDS) analysis showed that each element was distributed with in the particles. Er3+, Ho3+, and Yb3+ codoping was used to regulate the Yb3+ doping concentration, and under 980 nm excitation, the strongest upconversion emission was obtained for the prepared 1% Er3+, 1% Ho3+, 1% Yb3+ samples. Compared with that for the Er3+, Yb3+-doped Bi2WO6 sample, the luminescence intensity of the characteristic emission peak of Er3+ at 525 nm for the Er3+, Ho3+, Yb3+-doped sample was weakened, while the luminescence of the characteristic emission peak of Ho3+ was enhanced; these results indicated that energy transfer from Er3+ to Ho3+ occurred. The intensities of the four emission peaks at 525 nm, 546 nm, 660 nm, and 756 nm in the 1% Er3+, 1% Ho3+, 1% Yb3+-doped Bi2WO6 sample increased with increasing excitation pump power from 45 mW to 233 mW. Based on the relationship between the excitation pump power and the emission intensity, all four luminescence peaks originated from two-photon absorption. The fluorescence intensity ratio versus temperature was fitted using three different nonthermally coupled energy level pairs in the range from 298 K to 573 K. The maximum absolute temperature sensitivity of 0.296 K-1 was obtained at 573 K for the Ho3+ nonthermally coupled energy level pair, and the maximum relative temperature sensitivity of 0.279 K-1 was obtained at 298 K. The temperature resolution for characterization using the above nonthermally coupled energy level pairs was calculated, with the temperature resolution δT yielding a minimum value of 0.03 K. The CIE color coordinates at different temperatures were calculated, and the color coordinates gradually moved from the green region to the red region.