Realizing Bright-Dark Dual-Field Multimode Optical Signals in Photochromic Apatite Phosphors for Security Identification.

Regulating defect distribution in inorganic phosphors is paramount for realizing multimode dual-field optical signals for high security level identification but remains an ongoing challenge. Here, we propose a strategy of equivalent anion doping and nonequivalent cation doping to successfully regulate the trap distribution and density in Ba5(PO4)3Cl:F-,Eu2+,Ce3+ (BPCF-AG) phosphors. Due to the coexistence of shallow and deep traps for different photon processes, the BPCF-AG exhibits simultaneous photochromism in a bright field and tetramode luminescence (photoluminescence, afterglow, 980 nm photostimulated luminescence, and 650/532 nm photostimulated afterglow) in a dark field. The trap roles responsible for versatile optical behaviors are investigated by thermoluminescence curves, and a reasonable mechanism is proposed. In addition, we design a series of demonstrations for security identification and information encryption based on the dual-field multimode optical signals of BPCF-AG to illustrate its potential application scenarios.

Isolated Coordination Polyhedron Confinement in ABP2O7:Mn2+ (A = Ba/Sr; B = Mg/Zn).

Many research efforts have focused on designing new inorganic phosphors to meet different application requirements. The structure-photoluminescence relationship between activator ions and the matrix lattice plays an irreparable role in designing target phosphors. Herein, a series of ABP2O7:Mn2+ (A = Ba/Sr; B = Mg/Zn) phosphors are prepared for a detailed study on the relationship between the luminescence performance and spatial structure and symmetry of the doping site of Mn2+. Due to the weak interaction between nearest B-B pairs, [BO5] is defined as an isolated coordination polyhedron whose structure and symmetry directly influence the photoluminescence of Mn2+. The emission wavelength of Mn2+ is ∼620 nm when it occupies the triangular bipyramid [MgO5] in BaMgP2O7. When Mn2+ occupies the quadrangular pyramid-typed [MgO5] or [ZnO5] in SrMgP2O7, SrZnP2O7, and BaZnP2O7, the emission wavelengths peak at ∼670 nm. We propose a conception of isolated coordination polyhedral confinement to clarify the luminescence performance of Mn2+ in the fivefold coordination configuration with different geometries, which has great theoretical research significance for designing inorganic phosphors.

Broadband UV-Excitation and Red/Far-Red Emission Materials for Plant Growth: Tunable Spectrum Conversion in Eu3+,Mn4+ Co-doped LaAl0.7Ga0.3O3 Phosphors.

Broadband ultraviolet (UV) excitation and red/far-red emission phosphors can effectively convert solar spectrum to enhance photosynthesis and promote morphogenesis in plants. Based on the above application requirements, Eu3+ single-doped LaAl1-yGayO3 solid solutions and Eu3+,Mn4+ codoped LaAl0.7Ga0.3O3 phosphors were designed and synthesized in this work. The LaAl0.7Ga0.3O3:0.05Eu3+ (LAG:Eu3+) phosphor exhibits a strong charge transfer band (CTB) excitation and characteristic 5D0 → 7F2 transition red emission (619 nm), which is very similar to the luminescence properties of Eu3+-organic ligand compound (EuL3). Rietveld refinement studies further revealed that the cation substitution disturbs the site symmetry. The optimal Eu3+, Mn4+ co-doped LaAl0.7Ga0.3O3 (LAG:Eu,Mn) phosphor possesses a dual-band excitation spectrum in broadband ultraviolet (UVA, UVB) area and a dual-band emission spectrum within red/far-red area. Under the sunlight radiation, the real-time spectrum of luminous laminated glasses fabricated by coating the LAG:Eu,Mn phosphor shows the percentage of radiant intensity in the red/far-red region significantly increases, suggesting that the phosphor can be a promising candidate for solar spectral conversion in plant cultivation. We believe this work provides a new idea for developing novel broadband ultraviolet excitation and red/far-red emission phosphors.

Site Preference-Driven Mn4+ Stabilization in Double Perovskite Phosphor Regulating Quantum Efficiency from Zero to Champion.

The tetravalent-state stability of manganese is of primary importance for Mn4+ luminescence. Double perovskite-structured A2B'B″O6:Mn4+ has been recently prevalent, and the manganese ions are assumed to substitute for the B″(IV-VI)O6 site to stabilize at the tetravalent charge state to generate far-red emissions. However, some Mn-doped A2B'B″O6-type materials show no or weak luminescence such as typical Ca2MgWO6:Mn. In this work, a cation-pair co-substitution strategy is proposed to replace 2Ca2+ by Na+-La3+ to form Ca2-2xNaxLaxMgWO6:Mn. The significant structural distortion appears in the solid solution lattices with the contraction of [MgO6] but enlargement of [WO6] octahedron. We hypothesize that the site occupancy preference of Mn migrates from Mg2+ to W6+ sites. As a result, the effective Mn4+/Mn2+ concentration enhances remarkably to regulate nonluminescence to highly efficient Mn4+-related far-red emission. The optimal CaNa0.5La0.5MgWO6:0.9%Mn4+ shows an internal quantum efficiency of 94% and external quantum efficiency of 82%, reaching up to the top values in Mn4+-doped oxide phosphors. This work may provide a new perspective for the rational design of Mn4+-activated red phosphors, primarily considering the site occupancy modification and tetravalent-state stability of Mn.

Composition and Antithermal Quenching of Noninteger Stoichiometric Eu2+-Doped Na-ß-Alumina with Cyan Emission for Near-UV WLEDs.

Phosphors with high quantum efficiency and thermal stability play a key role in improving the performance of phosphor-converted white light-emitting diodes (pc-WLEDs). A near-UV-pumped LED shows a great advantage due to its reduction of the negative effect of blue light on human health. In this work, we propose a series of near-UV excitable cyan-emitting Eu2+-activated phosphors with a nominal composition of Na2-2xAl11O17+a:xEu2+ (x = 0.01-0.40), which crystallize in a sodium ß-alumina phase with a composition close to Na1.22Al11O17.11. An excess amount of the sodium carbonate raw material makes up the volatile Na during the high-temperature process. The noninteger stoichiometric composition promotes the rigidity of the crystal structure with a slight excess of Na insertion into layers between spinel blocks of the NaAl11O17 matrix. The nonequivalent substitution of Na+ by Eu2+ generates intrinsic defects acting as carrier traps. As a result, the phosphor with an optimal nominal composition Na1.6Al11O17+a:0.20Eu2+, under the excitation at 365 nm, shows an asymmetric cyan emission band at 468 nm with internal and external quantum efficiencies of 81.3 and 56.9%, respectively. Remarkably, the phosphor exhibits antithermal quenching within 200 °C. A pc-WLED with a high color rendering index (87.2) suggests great potential of the phosphor in pc-WLEDs. Therefore, a combination of a rigid structure and deep trap level is an effective way in exploring new phosphors with high quantum efficiency and thermal stability.

The Facile Dissociation of Carbon-Oxygen Bonds in CO2 and CO on the Surface of LaCoSiHx Intermetallic Compound.

In catalysis science, the electronic structure of the active site determines the structure-activity relationship of the catalyst to a large extent. Therefore, modulating the electronic structure has become a main route for the rational design of metal-based catalyst materials. In this work, we prepared a LaCoSiHx material that has more electronegativity and a lower workfunction than traditional supported Co-based catalysts. Using CO2 methanation as a model catalytic reaction, the facile dissociation of CO2 and CO (a key reaction intermediate) on the surface of the LaCoSiHx catalyst is observed by various experimental methods (e.g., in situ Raman and FTIR) at room temperature. Moreover, theoretical calculation results further show that LaCoSiHx has a much stronger capacity for carbon-oxygen bond activation than the Co surface. The intrinsic mechanism is attributed to the marked electron transfer from catalysts into the antibonding orbital of CO2 and CO.

Site Occupation and Spectral Assignment in Eu2+-Activated ß-Ca3(PO4)2-Type Phosphors: Insights from First-Principles Calculations.

Eu2+-activated ß-Ca3(PO4)2-type phosphors have attracted significant experimental interest for applications in solid-state lighting because of the presence of multiple cation sites, which is highly desirable for site engineering of activator emission. However, the site occupation and associated spectral assignment of dopant Eu2+, and hence the mechanism behind the site-regulated emission tuning, still remain elusive. Herein, we perform a systematic first-principles study on Eu2+-doped Ca3(PO4)2, Ca10M(PO4)7 (M = Li, Na, K), and Ca3(PO4)2:Mg by combining density functional theory and multiconfigurational ab initio calculations. The results show that, among the isovalent EuCa substitutions in Ca3(PO4)2, the occurrence probability correlates positively with the size of the substituted site, which is, nevertheless, weakened by the incorporation of codopant Mg2+ ions. In the presence of aliovalent EuM substitutions as in Ca10M(PO4)7, the site-size-controlled preference is neutralized by the requirement for charge compensation, and the effect becomes more pronounced with an increase of the M+ ionic size. On this basis, the emission spectra of the phosphors are interpreted with respect to the substituted sites and the mechanism behind the composition dependence of the emission color is consistently elucidated, as is also verified by a comparison between the calculated 4f → 5d transition energies and experimental excitation spectra. Our results provide a new perspective on the site preference of Eu2+ in ß-Ca3(PO4)2-type compounds and may also serve as a theoretical guideline on the structure-property relationship for the design of other Eu2+-activated phosphors.

Fine-Tunable Self-Activated Luminescence in Apatite-Type (Ba,Sr)5(PO4)3Br and the Defect Process.

Intrinsic defect-related luminescence has recently been attracting more research interest for the modification of phosphors. However, the connection between defect formation and crystal structure has never been considered. In this work, we report that in the absence of an impurity activator, under a reducing atmosphere, apatite-type compound M5(PO4)3X (M = Ca, Sr, or Ba; X = F, Cl, or Br) can emit tunable colors ranging from blue to orange depending on the content of M and X. To better understand the cause, Ba5- mSr m(PO4)3Br (BSPOB; m = 0-5) solid solutions were analyzed in detail. The dependency of self-activated luminescence on atmospheric conditions and solid solution compositions was investigated by combining experimental characterizations and theoretical calculations using density functional theory. Crystal structures of these solid solutions were verified by X-ray diffraction patterns as well as Rietveld refinements. With the defect formation energy and electron paramagnetic resonance measurement, we propose that an oxygen vacancy (VO) should be mainly responsible for the peculiar super wide band emission. Moreover, the enhanced distortion of solid solution crystal structures augments VO concentrations and leads to luminescence intensities in solid solutions that are higher than that in end point compounds. Variations of the electronic structure of BSPOB matrices with gradual tuning of the Sr/Ba ratio were also investigated. As a result, the introduction of VO defect levels within the band gap leads to the formation of donors and acceptors, allowing for a modulation of the photoluminescence throughout the visible part of the spectrum. As the first report in the literature to demonstrate fine-tunable emissions over a wide wavelength range as a consequence of native defective levels in a series of continuous apatite-type solid solutions, our results illustrate the feasibility of defect-meditated systems by carefully tailoring defect chemistry and nonstoichiometric chemical composition under controlled conditions to engineer phosphor properties.

Changing Ce3+ Content and Codoping Mn2+ Induced Tunable Emission and Energy Transfer in Ca2.5Sr0.5Al2O6:Ce3+,Mn2.

A series of color-tunable Ce3+ single-doped and Ce3+, Mn2+ codoped Ca2.5Sr0.5Al2O6 phosphors were synthesized by a high-temperature solid-state reaction. The crystal structure, luminescent properties, and energy transfer were studied. For Ca2.5Sr0.5Al2O6:Ce3+ phosphors obtained with Al(OH)3 as the raw material, three emission profiles were observed. The peak of photoluminescence (PL) spectra excited at ∼360 nm shifts from 470 to 420 nm, while that of the PL spectra excited at 305 nm stays unchanged at 470 nm with the increase of Ce3+ content. Furthermore, the peak of PL spectra is situated at 500 nm under excitation at ∼400 nm. The relationship between the luminescent properties and crystal structure was studied in detail. Ce3+, Mn2+ codoped Ca2.5Sr0.5Al2O6 phosphors also showed interesting luminescent properties when focused on the PL spectra excited at 365 nm. Obvious different decreasing trends of blue and cyan emission components were observed in Ca2.5Sr0.5Al2O6:0.11Ce3+,xMn2+ phosphors with the increase in Mn2+ content, suggesting different energy transfer efficiencies from blue- and cyan-emitting Ce3+ to Mn2+. Phosphors with high color-rendering index (CRI) values are realized by adjusting the doping content of both Ce3+ and Mn2+. Studies suggest that the Ca2.5Sr0.5Al2O6:Ce3+,Mn2+ phosphor is a promising candidate for near UV-excited w-LEDs.

Remarkably Enhancing Green-Excitation Efficiency for Solar Energy Utilization: Red Phosphors Ba2ZnS3:Eu2+, X- Co-Doped Halide Ions (X = Cl, Br, I).

Eu2+-activated Ba2ZnS3 has been reported as a red phosphor with a broad emission band peaking at 650 nm under blue excitation for white-LED. In this study, Ba2ZnS3:Eu2+, X- (X = F, Cl, Br, I) phosphors doped with halide ions were prepared by traditional high-temperature solid-state reaction. Phase identification of powders was performed by X-ray powder diffraction analysis, confirming the existence of single-phase Ba2ZnS3 crystals without dopant. The corresponding excitation spectra showed an additional broad band in the green region peaking at 550 nm when the phosphor was halogenated except by the smallest F-. It was proved that the green-excitation efficiency successively strengthened from Cl-, to Br-, to I-, which suggested larger halide ions made a greater contribution to the further splitting of the t2g energy level of the doped Eu2+ ions in the host Ba2ZnS3, and the optimized formula Ba1.995ZnS2.82:Eu2+0.005, I-0.18 showed a potential application in solar spectral conversion for agricultural greenhouse and solar cell. Defect chemistry theory and crystal field theory provided insights into the key role of halide ions in enhancing green-excitation efficiency.

Enhanced photoluminescence of the Ca0.8 Zn0.2 TiO3 :0.05% Pr3+ phosphor by optimized hydrothermal conditions.

The red-emitting phosphor Ca0.8 Zn0.2 TiO3 :Pr3+ was synthesized using an ethylene glycol (EG)-assisted hydrothermal method. The effects of additional amounts of and order of adding EG, plus hydrothermal temperature, time, and pH on the composition, morphology and optical properties of the titanate phosphors were studied. The crystalline phases of the titanate phosphors were confirmed to be constituted of a series of co-existing CaTiO3 , Zn2 TiO4 and Ca2 Zn4 Ti16 O38 compounds in various proportions that were visualized using an X-ray diffractometer (XRD). The optical properties of the phosphors were studied using photoluminescence spectra and UV-visible spectroscopy. The results show that the impurities Zn2 TiO4 :Pr3+ and Ca2 Zn4 Ti16 O38 :Pr3+ significantly contributed to the enhancement of an absorption band around 380 nm. The optimum Ca0.8 Zn0.2 TiO3 :Pr3+ phosphor consisting of appropriate amounts of CaTiO3 , Ca2 Zn4 Ti16 O38 and Zn2 TiO4 in three phases was achieved by controlling the hydrothermal conditions, and the obtained red phosphor exhibited the highest red emission (1 D2  â†’ 3 H4 transition of Pr3+ ) with an ideal chromaticity coordinate located at (x = 0.667, y = 0.332) under 380 nm excitation.

Clinical Usefulness of Ultrasound Elastography in Colonic Diseases: A Narrative Review.

Ultrasound elastography is an innovation of ultrasound technology that has developed since the 1990s. It has been successfully applied for many organs, such as the thyroid, breast, liver, prostate, and muscle systems, providing qualitative and quantitative information about tissue stiffness for clinical diagnoses. For colorectal tumors, ultrasound elastography can distinguish colon adenoma from colon adenocarcinoma and predict the chemotherapeutic effects of colon cancer by monitoring the stiffness changes of cancer tissue. In Crohn's disease, ultrasound elastography helps assess the stages of the course and guides further treatment strategies. Compared with colonoscopy, ultrasound elastography frees patients from the fears of uncomfortable procedures and enables operators to comprehensively observe the bowel wall and the surrounding structures. In this review, we introduced the principles and the pathological basis of ultrasound elastography and compared the diagnostic efficacies of colonoscopy with colonic ultrasound elastography. Meanwhile, we summarized the ultrasonography of colonic diseases and reviewed the clinical usefulness of ultrasound elastography in colonic diseases.

Ultrasound features affecting the sample adequacy after fine-needle aspiration of thyroid nodules with different risk stratification.

BACKGROUND: The inadequacy samples caused by the internal characteristic structure of thyroid nodules are difficult to be solved. OBJECTIVE: To evaluate the ultrasound features affecting the sample adequacy after fine-needle aspiration (FNA) of thyroid nodules with different risk stratification. METHODS: 592 thyroid nodules that underwent ultrasound-guided FNA were included in this retrospective study. The sample obtained by FNA were classified as inadequacy and adequacy according to the cytopathological results. Ultrasound features (ie., size, position, cystic predominance, composition, echo, shape, margin, and superficial annular calcification status) of the nodules were recorded and compared between the inadequacy sample group and adequacy sample group. RESULTS: Multiple logistic regression shows that preponderant cystic proportion (OR, 0.384; P = 0.041), extremely hypoechogenicity and hypoechogenicity (OR, 6.349; P = 0.006) were the independent influencing factors of inadequate samples after FNA in benign expected nodules. In addition, nodule size ≤10 mm (OR, 1.960; P = 0.010) and superficially annular calcification (OR, 4.600; P < 0.001) were independent influencing factors for inadequate samples after FNA in malignant expected nodules. CONCLUSION: The ultrasound features of hypoechogenicity or high cystic proportion in benign expected nodules and that of small size or annular calcification in malignant expected nodules were the risk factors for inadequacy samples by US-guided FNA.

Self-reduction-induced BaMgP2O7:Eu2+/3+: a multi-stimuli-responsive phosphor for X-ray detection, anti-counterfeiting and optical thermometry.

Mixed-valence Eu2+/3+-activated phosphors have attracted wide attention due to their excellent luminescence tunability. Steady control of the Eu2+/Eu3+ ratio is the key to achieving reproducible Eu2+/3+ co-doped materials. In this work, BaMgP2O7:xEu2+/3+ (BMPO:Eu, x = 0.001-0.20) was successfully prepared by the traditional solid-state method in air. Eu3+ undergoes selective self-reduction at Ba2+ sites surrounded by a [P2O7] framework, leading to quantitive Eu2+/Eu3+. The phosphors exhibit a blue-violet emission band at ∼410 nm due to 5d-4f transitions of Eu2+ and a group of red emission peaks from 5D0-7FJ of Eu3+. Controllable multicolor emissions are realized by regulating the Eu content and excitations. A linear response of overall luminescence intensity to irradiation dose makes the phosphor appropriate for X-ray detection. The combination of UV-blue excitation-dependent color evolution and X-ray luminescence qualifies the phosphors with great potential for multi-level anti-counterfeiting. In addition, Eu3+ presents abnormal anti-thermal quenching, so that the fluorescence intensity ratio (FIR) of Eu2+/Eu3+ changes in the temperature range of 300-520 K, suggesting a promising application in optical thermometry. Therefore, selectively partial self-reduction in a multi-cationic host is an effective strategy to design mixed-valence co-doped materials, providing a multiplicity of applications.

Novel Dual-Excitation and Dual-Emission Materials: Eu2+,Pb2+ Co-doped Core-Shell-Structured CaS@CaZnOS Phosphors and Their Application for Highly Efficient Photosynthesis of Plants.

Eu2+,Pb2+-doped core-shell-structured CaS@CaZnOS phosphors were synthesized by a two-step high-temperature solid-phase method. The as-synthesized CaS:Eu2+,Pb2+@CaZnOS:Pb2+ phosphors possess excellent dual-excitation and dual-emission (DE2) luminescent properties, which give rise to red emission peaking at 650 nm under green excitation, derived from the core CaS:Eu2+,Pb2+, and blue emission peaking at 424 nm, originating from the shell CaZnOS:Pb2+, under ultraviolet (UV) excitation. In addition, tunable red/blue emission can be achieved by changing the doping concentration of Pb2+ in the CaZnOS shell. The red/blue dual emission of core-shell DE2 phosphors under excitation of UV and green light significantly matches with the absorption spectrum of chlorophyll (a, b); hence, the as-prepared phosphors are excellent solar spectral conversion (SSC) auxiliaries of plastic films or laminated glass for greenhouses and provide ideas for creating more efficient and practically valuable SSC auxiliaries. The DE2 properties are described, and the energy transfer mechanism from Pb2+ to Eu2+ in the core is proposed and discussed in detail.

Composition Screening in Blue-Emitting Li4Sr1+xCa0.97-x(SiO4)2:Ce3+ Phosphors for High Quantum Efficiency and Thermally Stable Photoluminescence.

Photoluminescence quantum efficiency (QE) and thermal stability are important for phosphors used in phosphor-converted light-emitting diodes (pc-LEDs). Li4Sr1+xCa0.97-x(SiO4)2:0.03Ce3+ (-0.7 ≤ x ≤ 1.0) phosphors were designed from the initial model of Li4SrCa(SiO4)2:Ce3+, and their single-phased crystal structures were found to be located in the composition range of -0.4 ≤ x ≤ 0.7. Depending on the substitution of Sr2+ for Ca2+ ions, the absolute QE value of blue-emitting composition-optimized Li4Sr1.4Ca0.57(SiO4)2:0.03Ce3+ reaches ∼94%, and the emission intensity at 200 °C remains 95% of that at room temperature. Rietveld refinements and Raman spectral analyses suggest the increase of crystal rigidity, increase of force constant in CeO6, and decrease of vibrational frequency by increasing Sr2+ content, which are responsible for the enhanced quantum efficiency and thermal stability. The present study points to a new strategy for future development of the pc-LEDs phosphors based on local structures correlation via composition screening.

Site-sensitive energy transfer modes in Ca3Al2O6: Ce(3+)/Tb(3+)/Mn(2+) phosphors.

Ce(3+)/Eu(2+), Tb(3+) and Mn(2+) co-doping in single-phase hosts is a common strategy to achieve white-light phosphors via energy transfer, which provides a high color rendering index (CRI) value and good color stability. However, not all hosts are suitable for white-light phosphors due to inefficient energy transfer. In this study, the site-sensitive energy transfer from different crystallographic sites of Ce(3+) to Tb(3+)/Mn(2+) in Ca3Al2O6 has been investigated in detail. The energy transfer from purplish-blue Ce(3+) to Tb(3+) is an electric dipole-dipole mode, and the calculated critical distance (Rc) suggests the existence of purplish-blue Ce(3+)-Tb(3+) clusters. No energy transfer is observed from purplish-blue Ce(3+) to Mn(2+). In co-doped phosphors based on greenish-blue Ce(3+), however, the radiative mode dominates the energy transfer from Ce(3+) to Tb(3+), and an electric dipole-quadrupole interaction is responsible for the energy transfer from Ce(3+) to Mn(2+). A detailed discussion on the site-sensitive energy transfer modes might provide a new aspect to discuss and understand the possibilities and mechanisms of energy transfer, according to certain crystallographic sites in a complex host with different cation sites, as well as provide a possible approach in searching for single-phase white-light-emitting phosphors.