Phase transformations of 1-methylpiperidine under static and dynamic compression up to 21 GPa were investigated via in-situ Raman spectroscopy in a diamond anvil cell. Static compression reveals at least three crystalline phases and an amorphous state, which are kinetically sensitive and metastable. Dynamic compression rapidly induces amorphization, and subsequent decompression leads to spontaneous crystallization through Phase III and Phase II. The high-pressure phase behavior of 1-methylpiperidine is kinetically controlled rather than purely thermodynamic, governed by structural evolution, molecular flexibility, and metastable state formation.

GeAs exhibits excellent chemical stability and high in-plane anisotropy under ambient conditions. Pressure is one effective approach to regulate structures or properties of two-dimensional materials. In this work, the high-pressure effect on the phase transition and in-plane anisotropic properties is investigated for GeAs using Raman spectroscopy, infrared spectroscopy, high-pressure resistance measurement, and density functional theory calculations. The results show that GeAs undergoes an irreversible monoclinic-to-cubic transition around 18.4 GPa during compression. IR and resistivity measurements indicate that this cubic rock-salt structure exhibits a metallic state. Upon decompression, high-pressure cubic GeAs converts to a tetragonal structure rather than the initial monoclinic structure. Moreover, tetragonal GeAs also exhibits a metallic state. This transition is reversible, as tetragonal GeAs will convert back to cubic GeAs around 18.2 GPa. Angle-resolved polarized Raman spectroscopy reveals that for both Ag and Bg modes of monoclinic GeAs, pressure will induce a 10°-15° deflection in their polarization direction up to 10 GPa, but has no effect on their anisotropy periods. Tetragonal GeAs also exhibits excellent in-plane optical anisotropy with a period of 180°. But different from monoclinic GeAs, both the polarization direction and periods remain stable in its Raman mode under pressure. The result is conducive to understanding the structural stability and anisotropic properties of GeAs.

Designing low-dimensional hybrid organic-inorganic perovskites (HOIPs) with enhanced broadband emission under ambient conditions remains a pressing challenge. Here, interesting results of emission blueshift and enhancement were successfully achieved by pressure modulation of the (NH2(CH3)2PbI3 2 (CH 3 ) 2 PbI 3 ((NH2(CH3)2 2 (CH 3 ) 2 = DMA) structure. The observed rapid blueshifted emission is closely related to the distortion of PbI6 6 octahedron induced by phase transition from the P 6 3 / mc phase to the P 1 phase at 0.8 GPa, which has been confirmed by in situ highpressure PL, UV-vis absorption, synchrotron XRD and Raman spectroscopy. The pressure-induced PL enhancement of DMAPbI3 3 can be ascribed to the mechanism that the distorted PbI6 6 octahedrons promote the radiative recombination of self-trapped excitons by increasing the activation barrier energy for detrapping. The PL intensity enhancement was retained at 4 times the initial value after the pressure was released. These findings deepen the understanding of the structure-property relationships of one-dimensional perovskite and reveal the roles of pressure in regulating the optical properties of perovskites.

Solid-state topochemical polymerization (SSTP) reactions of diacetylenes (DAs) have garnered significant attention due to their crucial role in the synthesis and development of polydiacetylenes (PDAs). However, the SSTP reaction of bis(trimethylsilyl)-substituted diacetylene (BTMSDA) has not been reported until now due to its molecular stacking parameters seriously deviating from the conditions required for the SSTP reaction. To explore the possibility of the SSTP reaction of BTMSDA under high pressure, the structural evolution of BTMSDA in the range of 0∼12 GPa was investigated using diamond anvil cells combined with in situ Raman and infrared spectroscopy techniques. During compression, BTMSDA initially underwent a phase transition from DA-Ⅰ to DA-Ⅱ around 1.2 GPa. Subsequently, BTMSDA simultaneously experienced an SSTP reaction and another phase transition around 6.5 GPa, resulting in an uneven blue mixture consisting of the PDA-blue phase of Poly-BTMSDA and the DA-Ⅲ phase of BTMSDA. Upon decompression, the uneven blue mixture transformed into an uneven red mixture comprising the PDA-red phase of Poly-BTMSDA and the DA-Ⅰ phase of BTMSDA. Analysis reveals that the phase transitions were reversible, whereas the SSTP reaction was irreversible. Moreover, the first phase transition played a pivotal role in facilitating the SSTP reaction, while the second phase transition exhibited a competitive relationship with the SSTP reaction. This study not only deepens our understanding of the physicochemical properties of BTMSDA but also demonstrates the SSTP reaction of BTMSDA under high pressure.

Chalcopyrite copper-indium-gallium diselenides (CIGS) have emerged as promising materials with remarkable electronic properties and potential applicability to high-efficiency solar cells. The crystal and electronic structures of CIGS can be continuously tuned from their initial states under pressure. Although pressure-induced band gap closure in CIGS has been predicted in extensive theoretical studies, it has not been supported by experimental evidence. Here, we comprehensively investigate the pressure-dependent optical, electronic, and structural properties of Cu(In0.7Ga0.3)Se-2 up to 42.6 GPa. Our experimental results reveal an irreversible electronic transition from the semiconducting to the metallic state at 14.3 GPa. Under compression, the Cu(In0.7Ga0.3)Se-2 structure evolves from a tetragonal I42d phase to an orthorhombic Pna2(1) phase, which has not been previously reported in chalcopyrite. More intriguingly, the Pna2(1) phase is irreversible and possesses smaller Cu-Se and In/Ga-Se bond lengths and a smaller Cu-Se-Cu bond angle than the I42d phase. Density functional theory calculations indicate a lower enthalpy of the Pna2(1) phase than that of the I42d phase at pressures above 10.6 GPa. Meanwhile, density of states calculations illustrate that metallization arises from the overlap of the Se p and Cu d orbitals as the bond length reduces. This pressure-induced behavior could facilitate the development of novel devices with various phenomena involving strong coupling of the mechanical, electrical, and optical properties of chalcopyrite.

Near-infrared (NIR) phosphor tetragonal K3GaF6:Cr3+ with the space group of I41/a is synthesized through the coprecipitation method, which shows a broadband emission from 600 to 950 nm due to the 4T2→4A2 transition at ambient condition. The luminescent properties and phase transition of K3GaF6:Cr3+ are investigated under different temperatures and pressures using luminescence spectra and Raman spectra. K3Ga0.95F6:0.05Cr3+ undergoes two phase transitions at 170°C and 230°C respectively, but Cr3+ exhibits similar broad emission in three different structures. Different from a sequence of phase transitions upon heating, no phase transition is observed up to 22 GPa. However, pressure-induced crossover of the 4T2 and 2E states presents at 9.3 GPa, resulting in dominant narrow-band emissions from the 2E→4A2 transition at higher pressure. These results suggest that pressure can regulate the luminescence properties of K3GaF6:Cr3+ phosphor effectively. This work will deepen the understanding of Cr3+-doped fluoride, which is helpful to expand the application of NIR luminescent materials under extreme conditions.

The structural versatility of organic compounds imparts manifold properties to hybrid organic−inorganic perovskites, where two-dimensional (2D) halide perovskites are potential future platforms for light-emitting devices because of their unique quantum well configuration and dielectric confinement. Notwithstanding the numerous studies on the organic−inorganic perovskites carried out to date, precisely charactering the structure and photoluminescence mechanism remain considerable challenges. Herein, by applying Rietveld refinement, we have obtained crystal structure and atomic sites of 2D layered OA2PbBr4 perovskite, which undergoes a phase transition at 190 K with activation energies of 29.6 and 3.8 meV for the two phases, respectively. The theoretical analysis based on the crystal structure were performed to understand the nature of vibrations and band structure. Steady-state PL shows a narrow emission and a broad emission located at 409 and 487 nm, respectively. With temperature cooling down to 118 K, narrow emission gradually narrowed and enhanced. Meanwhile, intensity of broad emission first weakens and then increases. The turning point occurs near 198 K. By applying time-resolved PL (TRPL) and transient absorption (TA) spectra experiment, we observed a rapid carrier transfer from the FE to the STE state, and demonstrated the narrow and broad bands originate from free exciton and self-trapped exciton emission, respectively. And the self-trapping depth is proved to be 26.3 meV by low-temperature PL. Our findings indicate the synthesized 2D perovskite has potential applications in optoelectronic and display devices.

Temperature and pressure are two effective methods to tune the structure and luminescence properties of phosphors. In this study, tetragonal K3AlF6: Cr3+ phosphors were synthesized through the solid-state method. Its structure stability and luminescence property were in situ studied under temperature and pressure using differential scanning calorimetry (DSC), Raman, and photoluminescence spectra. At ambient conditions, one broadband emission presented in the 1.3-1.9 eV range due to the T-4(2)->(4)A(2) transition. Three phase transitions presented with increasing temperature to 400 degrees C, but no much change was observed for its luminescence property. In contrast, its structure was stable during compression, and no phase transition was observed up to 26.1 GPa. Furthermore, the crystal field around Cr3+ was enhanced under pressure, leading to its luminescence changing from broad T-4(2)->(4)A(2) emission to narrow E-2 ->(4)A(2) emission above 4.2 GPa. It was suggested that pressure was more effective for K3AlF6:5%Cr3+ phosphor. This result provides one effective method to modulate the luminescence property of Cr3+.

Near-infrared (NIR) phosphor tetragonal K 3 GaF 6 :Cr 3+ with the space group of I 4 1 / a is synthesized through the coprecipitation method, which shows a broadband emission from 600 to 950 nm due to the 4 T 2 -> 4 A 2 transition at ambient condition. The luminescent properties and phase transition of K 3 GaF 6 :Cr 3+ are investigated under different temperatures and pressures using luminescence spectra and Raman spectra. K 3 Ga 0.95 F 6 :0.05Cr 3+ undergoes two phase transitions at 170 degrees C and 230 degrees C respectively, but Cr 3+ exhibits similar broad emission in three different structures. Different from a sequence of phase transitions upon heating, no phase transition is observed up to 22 GPa. However, pressure-induced crossover of the 4 T 2 and 2 E states presents at 9.3 GPa, resulting in dominant narrow-band emissions from the 2 E -> 4 A 2 transition at higher pressure. These results suggest that pressure can regulate the luminescence properties of K 3 GaF 6 :Cr 3+ phosphor effectively. This work will deepen the understanding of Cr 3+ -doped fluoride, which is helpful to expand the application of NIR luminescent materials under extreme conditions.

Near-infrared light can be widely used in non-destructive testing, sensing, and night vision. Recently, phosphor-converted LED (pc-LED) based on near-infrared (NIR) phosphor have attracted considerable interest. In this work, tetragonal structured K3AlF6:Cr3+ phosphors were synthesized using the co-precipitation method. Cr3+ ions occupy the octahedral position, and its Dq/B value (the parameter describing the crystal field strength) is calculated to be 2.08, suggesting a weak crystal field. Upon blue light excitation (430 nm), a broadband NIR emission is observed in the range of 650–900 nm, corresponding to the spin-allow 4T2 → 4A2 transition. Increasing Cr3+ concentration, red-shift is observed in its NIR emission with the maximum emission intensity at 5 mol

The structural dynamics and phase behavior of 1-ethyl-3-methylimidazolium trifluoroacetate ([Emim][CF3AcO]) under elevated pressure conditions were meticulously examined. Utilizing a diamond-anvil cell (DAC) in conjunction with Raman spectroscopy and synchrotron radiation X-ray diffraction, investigations were conducted at ambient temperature. Synchrotron radiation X-ray diffraction spectra revealed the absence of crystallization in the samples at pressures up to 5 GPa. A detailed analysis of the Raman spectra elucidated the relationships between Raman shift and full width at half maxima (FWHM) of characteristic Raman peaks as a function of pressure. A notable discontinuity was observed around 2.8 GPa, suggestive of a potential phase transition at this threshold. The hydrostatic properties of [Emim][CF3AcO] were further elucidated through analysis based on the ruby fluorescence peak under high-pressure conditions. These findings indicate a pressure-induced transition of [Emim][CF3AcO] at approximately 2.8 GPa, transitioning from a liquid state to a superpressurized glass. In addition, the conformational equilibrium of [Emim][CF3AcO] under such high-pressure environments was meticulously analyzed. The study revealed the coexistence of two conformers, namely planar and nonplanar, under high-pressure conditions. It was observed that the population of planar conformers escalates with increasing pressure, attributable to their reduced conformational volume. This research provides novel insights into the high-pressure behavior of imidazolium-based ILs, contributing significantly to the understanding of their phase transitions and conformational dynamics under extreme conditions.

This work is devoted to the effect of pressure on the structure of lamivudine by using Raman and infrared spectroscopy in diamond anvil cells. The results showed a transition from tetragonal crystal Form II to an un-known Form III' at approximately 1.26 GPa, followed by a transition from Form III' to Form IV' at pressure of 7.23 GPa. The phase transitions were marked by unique profiles and pressure-dependent characteristic modes. Pressure-induced changes in structural symmetry led to conformational transition in lamivudine. Furthermore, there was a considerable conformational variation between A and D in lamivudine molecule to maintain structural balance. Spectroscopic measurements indicated that these pressure-induced changes were reversible below approximately 0.1 GPa.

At present, ionic liquids' high production and use costs are limiting their large-scale applications, so how to recycle them has attracted great attention. Crystallization processes are extremely important for developing new recycling technologies for ionic liquids, and cooling rates have important effects on the crystallization processes. Based on these, in this paper, polarizing microscopy, small angle X-ray scattering and Raman spectroscopy were employed to research the phase transitions and the structural changes of 1-dodecy1-3-methylimidazolium tetrafluoroborate ([CI,mim][BF4]) from 60 to 0 V at the cooling rates of 30 and 1 C " min, in order to reveal the effect of cooling rates on the crystallization process and product. POM results show that [C12 Mini] BEi I experienced the phase transitions from the liquid state to liquid crystal state and then to crystal state I during the rapid cooling process, and that [C12 Mim] [BF] underwent the phase transitions from the liquid state to liquid crystal state and then to crystal state II during the slow cooling process. The crystal state I consisted of many "ball-like" crystals with large sizes, while the crystal state II was composed of a lot of "needle-like" crystals with small sizes. In addition, SAXS results show that [C12 Mini] [BE,] has two crystal structures, including perpendicular and triclinic bilayer phases. Both were found simultaneously in the crystal state I but only the triclinic bilayer phase appeared in the crystal state II. Therefore, crystal state I is a mixed phase crystal, while crystal state II is a single phase crystal. Furthermore, it can be concluded from the Raman results of [C12 Minl] BF4 that the [C12mim]+ in the perpendicular bilayer phase is the G conformation, and that the [C1.2mim]+ in the triclinic bilayer phase is the A conformation. In conclusion, [C1.2 [BE, I underwent the phase transitions from the liquid state to liquid crystal state and then to crystal state I at a rapid cooling process, and a mixed phase crystal composed of the perpendicular bilayer phase and the triclinic bilayer phase was obtained. However, [C12 Min]] BEi I underwent the phase transitions from the liquid state to liquid crystal state and then to crystal state II at a slow cooling, and a single phase crystal consisting of the triclinic bilayer phase was obtained. What is more, the mixed phase crystal includes the G conformation and the A conformation of [C12 Mini] while the single phase crystal only contains the A conformation. So, the cooling rate has an important effect on the crystallization process and product of [C12 Min]] BEi 1. These results provide important experimental data for enhancing the recovery technology of [C12 Mini] BF4 and are also helpful in investigating the phase transition and structure change of similar ionic liquids.

Alkanes are an important part of petroleum, and the phase structure and stability of alkanes in the deep earth are of great significance for petroleum exploitation. In this work, we performed Raman spec-troscopy of cyclohexane under static and dynamic pressures at room temperature. Cyclohexane under-went four solid-solid transitions near 0.66, 1.57, 3.39 and 13.59 GPa during static compression up to 25 GPa. Under dynamic compression, two new phases IV'and V'of cyclohexane were found at 2.23 GPa and 3.98 GPa, respectively, as the pressure increased from 0.91 GPa to 2.23, 3.98, 5.65, 6.80 and 7.45 GPa step by step within 5 ms. At a higher compression rate, cyclohexane turned from phase IV into phase VI' as the pressure increased from 2.77 to 20.74 GPa within 5 ms. The Raman results show that the cyclohexane molecule forms a geometric structure with low symmetry under dynamic pressure. We speculated that dynamic compression provides a high-pressure and temperature nonequilibrium path for cyclohexane, which could compel molecules to adjust and rearrange to form new phases.(c) 2022 Elsevier B.V. All rights reserved.

在自制的马里奥特装置上测量了不同条件下水的流速,验证了马里奥特装置的恒流特性,并探讨了其恒流特性的影响因素.在马里奥特装置提供恒流的条件下,对流管进行了不同形式的组装.通过测量流管中不同位置处水的压力,流速及高度差,实验验证了水的伯努利方程.设计总-支流管实验,测量总流管与支流管中的参数,发现总流管的伯努利常数(C)等于各支流管之和,拓展了伯努利方程在分支流管中的应用.

The phase transitions of carbon tetrachloride under static and dynamic compression were measured by high-pressure Raman spectroscopy. Under a static compression of up to 10 GPa, carbon tetrachloride underwent five phase transitions at approximately 0.25 GPa, 0.45 GPa, 0.71 GPa, 2.26 GPa and 7.32 GPa. An obvious liquid-liquid phase transition of carbon tetrachloride was observed at approximately 0.25 GPa. The appearance of the metastable liquid could be attributed to a mild thermodynamic process enabled by small increases in pressure. Under dynamic compression, liquid carbon tetrachloride was solidified by rapid compression from approximately 0.40 GPa to 1.57 GPa, 2.26 GPa and 2.87 GPa. It was found that liquid carbon tetrachloride could solidify to form a metastable phase (amorphous or nanocrystalline) along with a pressure jump. Interestingly, the phase transition behavior was not influenced by the rapid compression of the solid carbon tetrachloride. The unusual phase transition of carbon tetrachloride can be explained by pressure-induced supercooling and the fast compression rate. (C) 2021 Elsevier B.V. All rights reserved.

采用高温固相法合成出正交相和三斜相结构的BiNbO4:Eu3+样品,利用X射线衍射(XRD)、拉曼光谱、吸收光谱和荧光光谱对样品的结构和光学性能进行了研究.结果表明:900℃合成样品为正交相结构α-BiNbO4,而1200℃得到三斜相结构β-BiNbO4.吸收光谱得到α相和β相BiNbO4的光学带隙分别为2.69 eV和2.96 eV,与第一性原理的理论结果2.640 eV和3.032 eV相吻合.Eu3+掺杂诱导二者的光学带隙蓝移至2.89 eV和3.05 eV,有效改变了其光响应范围.荧光光谱表明:Eu3+在两种结构的最强荧光峰均来自5 D0→7 F2电偶极跃迁,最强荧光峰分别位于615 nm和611 nm.Eu3+在β-BiNbO4中的荧光强度更高,而且其5 D0→7 F2和5 D0→7 F1的荧光强度比值更大.与Eu3+相似,Er3+在β-BiNbO4中具有更高的上转换荧光强度,其强度约是在α-BiNbO4中荧光的近40倍,说明三斜结构BiNbO4更适合做稀土离子的基质材料.

氟氧化物兼有氧化物优异的稳定性和氟化物的低声子能量,是上转换发光材料的一种热点基质材料,因而研究六方相LaOF:Er,Yb的上转换发光性能及其温度特性具有重要意义.本文采用水热法制备了六方相LaOF:Er,Yb荧光材料,通过X射线衍射(XRD)、扫描电镜(SEM)和荧光光谱对其结构和上转换荧光性能进行表征.实验结果表明,水热法120℃得到六方相LaF3,经800℃和1000℃退火后分别形成四方相LaOF和六方相LaOF.980 nm激发下,六方相LaOF:Er,Yb中Yb3+与Er3+存在能量传递,通过双光子吸收产生绿光和红光的上转换荧光,并且Yb3+与Er3+的最佳浓度分别为3％和1％.最后研究了六方相LaOF:Er,Yb在温度传感方面的应用,其在150～400 K温度范围的相对灵敏度和绝对灵敏度分别为0.037 K-1和0.0043 K-1.该材料具有优异的温度传感特性,对荧光温度传感器件的设计和应用具有指导意义.