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In this paper, an experimental setup composed of a color-mixing device, power supply, and spectrometer is developed. This setup is available for students to do hands-on color mixing with red, green, and blue light in undergraduate labs. LED volt-ampere and spectrum characteristics are investigated. The apparatus was used to perform additive color mixing, and visual colorimetric parameters such as color coordinates, dominant wavelength, and color purity were obtained. This will help students understand the physics of LEDs and chromaticity. In addition, this experiment is useful in introducing topics such as the CIE chromaticity diagram and human perception of colors.

As a new type of energetic material, cocrystal explosives demonstrate many excellent properties, such as high energy density and low sensitivity, due to the interaction between the molecules of the two components.

Laser-induced damage threshold is the main limitation for fused silica optics in high-power laser applications. The existence of various defects near the surface is the key factor for the degradation of the threshold. In this work, the photoluminescence spectra at different regions of the damaged and recovered fused silica samples are recorded to analyze the correlation between photoluminescence of surface defects and laser-induced damage threshold. The experimental data concluded the inverse proportional correlation between fluorescence and laser-induced damage threshold value. The weak photoluminescence is the guarantee of the high laser-induced damage threshold, and then the higher local Si nanocluster concentration corresponds with the higher laser-induced damage threshold value for the fused silica optics after CO2 laser treatment. The investigation reveals that photoluminescence measurement can be employed to check the quality of pristine fused silica and evaluate the tendency of the laser-induced damage threshold value. The current results are helpful for understanding the evolution of interaction from CO2 laser treatment and fused silica optics and can provide the guide of process technology for the high quality of fused silica optics.

In this work, Ag@CdS nanowires (NWs) were fabricated via a facile hydrothermal route and magnetron sputtering. The structure and morphology of the Ag@CdS NWs were characterized by field emission sc...

Previous investigations had revealed that β-RDX facilely transforms to α-RDX due to the poor crystalline quality. This hindered obtaining insights into the β-RDX pressure behavior. In this work, ph...

The refinement of XRD patterns only provides the average structure parameters for the alloying materials because of the symmetric protection. Raman vibrational modes can append the detailed information about the bond length and structure. The refinements of XRD patterns for Bi alloying Cs2AgInCl6 revealed the strong structure distortion with the enlarged octahedron of In(Bi)Cl6 and the contracted octahedron of AgCl6 with the increasing Bi. Raman spectra supported the expanded octahedron of InCl6 and the reduced octahedron of AgCl6 but identified the anomalous shortening bond length of Bi-Cl with the increasing Bi. These distorting octahedrons break parity forbidden transition, modify Huang-Rhys factor, and result in the maximum values at 30% Bi alloying and the same variation trend for both photoluminescence and Huang-Rhys factor with the increasing Bi alloying.

Van der Waals (vdW) chemistry in simple molecular systems may be important for understanding the structure and properties of the interiors of the outer planets and their satellites, where pressures are high and such components may be abundant. In the current study, Raman spectra and visual observation are employed to investigate the phase separation and composition determination for helium-nitrogen mixtures with helium concentrations from 20 to 95% along the 295 K isothermal compression. Fluid-fluid-solid triple-phase equilibrium and several equilibria of two phases including fluid-fluid and fluid-solid have been observed in different helium-nitrogen mixtures upon loading or unloading pressure. The homogeneous fluid in helium-nitrogen mixtures separates into a helium-rich fluid (F

Thermal mechanical responses under high temperature and high pressure are basic information to understand the performance of energetic materials. In this work, the pressure effects on the thermal decay of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) are explored. Up to the initial pressure of 4.6 GPa, the pressure dependent decomposition boundary is built and no phase transition occurs until the decomposition of the LLM-105 crystal. The decomposition temperature is significantly lifted

The pressure-induced structural phase transitions of e- and γ-CL-20 were studied by Raman and mid-infrared spectroscopy up to 60 GPa. In this work, the phase transition of CL-20 from the e-phase to...

The electronic structural evolution of LLM-105 crystal under high pressure and low temperature is investigated by photoluminescence, absorption, Raman spectra, and density functional theory (DFT) c...

Phase transitions of the β-HMX crystal have been systematically studied via Raman, mid-infrared, and X-ray diffraction techniques under high pressures of up to 40 GPa. When using a neon pressure tr...

In this work, Mn2+-doped ZnS nanorods were synthesized by a facile hydrothermal method. The morphology, structure, and composition of the as-prepared samples were investigated. The temperature-dependent photoluminescence of ZnS:Mn nanorods was analyzed, and the corresponding activation energies were calculated by using a simple two-step rate equation. Mn2+-related orange emission (4T1 → 6A1) demonstrates high stability and is comparatively less affected by the temperature variations than the defect-related emission. A metal–semiconductor–metal junction ultraviolet photodetector based on the nanorod networks has been fabricated by a cost-effective method. The device exhibits visible blindness, superior ultraviolet photodetection with a responsivity of 1.62 A/W, and significantly fast photodetection response with the rise and decay times of 12 and 25 ms, respectively.

${\mathrm{Co}}_{2}$-based Heusler alloys show diverse magnetic behavior, extending from the localized Heisenberg to the delocalized itinerant, and thus cannot be generalized with one specific model. Therefore, we bring together experiments and first-principles calculations to reveal the origin of long-range ferromagnetism in the ${\mathrm{Co}}_{2}$-based Heusler alloy ${\mathrm{Co}}_{2}\mathrm{HfSn}$. The precise value of the critical exponents $\ensuremath{\beta}=0.471(4), \ensuremath{\gamma}=1.02(4)$, and $\ensuremath{\delta}=3.273(5)$ with the Curie temperature ($T{}_{c}=430$ K) were determined experimentally by means of different analytical methods such as modified Arrott plot analysis, the Kouvel-Fisher method, and critical isotherm analysis. The deduced critical exponents belong to the theoretical prediction of the three-dimensional mean-field model. The magnetic exchange distance is found to decay as $J(r)\ensuremath{\sim}{r}^{\ensuremath{-}4.52}$, indicating the long-range magnetic interaction in ${\mathrm{Co}}_{2}\mathrm{HfSn}$. Moreover, the magnetic entropy change $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}$ features a maximum at ${T}_{c}$, i.e., $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}^{max}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}$ 29.87(6) J ${\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{4pt}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ at 5 T, whereas power law fitting of $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}^{max}$ with $H$ gives ${n}^{\ensuremath{'}}=0.663(5)$, also confirming the mean-field-type magnetic interaction in ${\mathrm{Co}}_{2}\mathrm{HfSn}$. Meanwhile, in order to explore the origin of long-range ferromagnetic ordering in ${\mathrm{Co}}_{2}\mathrm{HfSn}$, spin-polarized density functional theory calculations were employed in this study. No stable antiferromagnetic solution with stable local magnetic moments at the Co or Hf site was observed in our fixed spin moment simulation, revealing that ${\mathrm{Co}}_{2}\mathrm{HfSn}$ is a highly itinerant magnet with a long-range ferromagnetic solution together with robust half-metallic conduction stable against thermal excitation higher than room temperature. Furthermore, our theoretical analysis shows that ${\mathrm{Co}}_{2}\mathrm{HfSn}$ belongs to an unconventional family of itinerant magnetism. Both the 100% spin-polarized metallicity and ferromagnetism arise from the Co $d$ orbitals, causing it to be unique compared to the conventional itinerant family of Ni, Co, or Fe, where magnetism and metallicity originate from different orbitals characters.

The refinement of XRD patterns only provides the average structure parameters for the alloying materials because of the symmetric protection. Raman vibrational modes can append the detailed information about the bond length and structure. The refinements of XRD patterns for Bi alloying Cs

3,3′-Diamino-4,4′-azoxyfurazan (DAAF) is a new energetic material and has potential for application in many fields. Few works about its luminescence under high pressure have been reported so far. To probe its behavior of emission and electronic structure evolution, fluorescence, absorption, Raman, and Fourier transform infrared spectroscopies were performed under high pressure. Time-dependent density functional theory was carried out to reveal the luminescence mechanism of DAAF under ambient conditions. The yellow-green emission of DAAF mainly originated from the π* → π transition. The absorption edge shifted to red, and the color changed from yellow to dark with the increasing pressure. Two electronic structure changes were observed at ∼3 and ∼12 GPa because of the variation of hydrogen bond network and distortion of the molecular structure. The strengthened secondary bonding interactions and a slightly enlarged π-conjugation system resulted in the evident enhancement in the fluorescence intensity and mo...

The new energetic material 2,6-diamino-3,5-dinitropyrazine-1-oxide (C4H4N6O5, LLM-105) maintains its structural stability under high pressure below 30 GPa at room temperature or in the temperature ...

During the last few years, the organic–inorganic hybrid methylammonium lead halide perovskite, CH3NH3PbX3 (MAPbX3, X = I–, Cl–, Br–), has received great interest in the field of photovoltaics. Rele...

In situ Raman spectra of HoVO4 micro- and nanocrystals were obtained at high pressures up to 25.4 and 18.0 GPa at room temperature, respectively. The appearance of new peaks in the Raman spectra and the discontinuities of the Raman-mode shift provided powerful evidence for an irreversible zircon-to-scheelite structure transformation for HoVO4 microcrystals at 7.2 GPa and for HoVO4 nanocrystals at 8.7 GPa. The lattice contraction caused by the size effect was thought to be responsible for the different phase-transition pressures. Also, the higher stability of HoVO4 nanocrystals compared with the microcrystals was also confirmed using the Raman frequencies and pressure coefficients. The results of the phase transition of HoVO4 were compared with previously reported rare-earth orthovanadates, and the phase diagram of REVO4 with RE ionic radius at different pressures was presented.

Ultrasmall pure hexagonal phase NaYF4:Yb,Er is successfully prepared via the solvothermal method. The upconversion (UC) luminescence of hexagonal phase NaYF4:Yb,Er nanocrystals is ten times stronger than that of cubic phase nanocrystals with the same size of 6 nm. XRD results reveal that heating above 673 K leads to conversion of the hexagonal phase to the high-temperature cubic phase, whereas the cubic nanocrystals undergo phase transformation from normal cubic at room temperature to hexagonal at 673 K and further to high-temperature cubic above 773 K. The hexagonal nanocrystals exhibit emission enhancement after heat treatment up to 573 K. Further heating above 773 K induces a decreasing trend in emission due to the phase transition to the high-temperature cubic phase. The cubic phase exhibits decreasing luminescence with temperature due to strong cross relaxation and then increasing luminescence above the temperature of 673 K due to the hexagonal phase transformation. The luminescent properties of both...

In this work Sr doped BiFeO3 (BSFO) and CoFe2O4 (CFO), (BSFO-CFO) composite polycrystalline samples are prepared via simple solid state route. We report the existence of an irreversible room temperature field-induced a ferromagnetic (FM) transition that does not quench even after removing the magnetic field in BSFO and CFO composite system. The field induced FM order transition occurs over a long range of temperature from 330 K to 5 K and remain stable for at least 45 min after the field quenching. The fraction of field induced FM phase increases and its decay rate decreases at lower temperatures. The strong temperature dependence of the magnetic field induced FM phase is also observed. These findings will lead the researcher to design new composite materials system for desired applications.

To probe the behavior of structural evolution and optical properties in solid energetic material TATB, X-ray diffraction (XRD) and Raman and absorption spectroscopy were performed under high pressure up to 20 GPa. The absorption edge shifts to red, and the color significantly varies with increasing pressure for TATB. The XRD patterns under high pressure indicate that TATB maintains the triclinic structure within this pressure range. An electronic structural change is observed at ∼5 GPa, resulting from the modification of conformers of TATB, which is associated with the rotation of nitro and amino groups under high pressure. The current experimental results clarified the absence of phase transition below 20 GPa and confirmed that the pressure-induced color change originates from the enhancing conjugation of π orbital due to the shorting C–NO2 bonds and the rotation of nitro groups with increasing pressure. The third-order Birch–Murnaghan equation of state is obtained up to 16.5 GPa, which is helpful for ca...

The transport and magnetic properties of LaAlO3/SrTiO3 (LAO/STO) heterostructure have been studied during cooling and warming. The strain gradient perpendicular to the surface of the heterostructure increases with the thickness of LAO film. The conductivity accelerated recoveries (CAR) are found at 80 K and 176 K in the interface of LAO/STO sample with millimeter scale, and are more obvious for thicker LAO layers during warming. These two recovering temperatures correspond to the migrating energies of oxygen single vacancy and divacancy trapped by polarized domain walls, separately. This indicated that domain walls diffuse along the longitudinal direction and expand to larger area due the strain gradient perpendicular to the interface. The stable and precise accelerating recovering temperatures make the sample at a larger scale a potential widely applied temperature standard reference. The magnetization measurements reveal the coexistence of paramagnetic and diamagnetic in the LAO/STO samples at whole temperature from 2 K to 300 K. The abnormal electric resistance rise is observed with the decreasing temperature below 25 K for the samples of 7 and 15 LAO layers. This anomaly is attributed to the Kondo effect below 25 K and weak anti-localization below 5 K due to the weightier paramagnetic content. The larger diamagnetic content suppresses these contributions in 25 LAO layers sample. This work provided an insightful view that the strain modified structure domain leads to the enhancement of CAR effect, which helps to achieve a better understanding of domain related physics in the LAO/STO system.

The temperature dependent optical constants of VO2 thin films with different thicknesses on variable substrates were measured by spectroscopic ellipsometry. The exact interband transition energies crossover metal-to-insulator transition of VO2 were obtained using a standard critical point model fitting based on the measured optical constants. The dynamic image of all critical points was obtained during the heating and cooling processes within the measured energy region. By introducing the fine orbital structure into the band model, every critical point was assigned to the corresponding band transition. The critical point of 4.7 eV predicted theoretically, which is response to the transition from O2P to upper a1g, was obtained experimentally for the first time. Our work provides a new view for the complex band scheme of the monoclinic and rutile phase VO2. Moreover, the insulator-to-metal transition temperature is modified by regulating both film thickness and substrate.

A simple model based on the measured fictive temperature distribution of fused silica was developed to determine the residual stress field of localized CO2 laser-heated fused silica with an unknown thermal history. The proposed model assumes that the initial frozen-in state of fused silica is the zero-point of residual stresses and the generation of residual stresses results from the thermoelastic contraction differences of fused silica with different fictive temperatures from initial frozen-in temperatures to the ambient temperature. The spatially resolved fictive temperatures of the fused silica sample were characterized using confocal Raman microscopy, and the calculated residual stress fields agreed well with laser-induced critical fracture measurements and photoelastic measurements.

1,3,5-Trinitrohexahydro-s-triazine (RDX) single-crystal particles crystallized in the β phase have been successfully grown by sublimation–recrystallization. Synchrotron X-ray diffraction results confirm that the recrystallized products are β-RDX single crystals. Compared to the traditional solution deposition methods, the sublimation method used in this work breaks through the mass limitations during the growth of β-RDX. The distribution of α- and β-RDX on different substrates reveals that hydrophilic substrates are prone to grow β-RDX single crystals and that hydrophobic substrates prefer α-RDX single crystals. The sublimation rate dominates the growth of pure β-RDX. The mechanisms of the phase transition from β-RDX to α-RDX during the process of sublimation–recrystallization have been studied. The current results can promote the potential application of β-RDX in the propellant, explosives, and military fields.

The critical behavior of Heusler alloy $\mathrm{Co}{}_{2}\mathrm{TiSn}$ is investigated by bulk magnetization study around the paramagnetic to ferromagnetic transition. The precise value of Curie temperature ($T{}_{c}=358\phantom{\rule{4pt}{0ex}}\mathrm{K}$) as well as the critical exponents ($\ensuremath{\beta}=0.527\ifmmode\pm\else\textpm\fi{}0.003, \ensuremath{\gamma}=1.229\ifmmode\pm\else\textpm\fi{}0.002$, and $\ensuremath{\delta}=3.33\ifmmode\pm\else\textpm\fi{}0.002$) were determined by means of different analytical methods such as modified Arrott plot analysis, the Kouvel-Fisher method, and critical isotherm analysis. With these critical exponents the isotherm $M(H)$ curves below and above $T{}_{c}$ collapse into two universal branches, fulfilling the single scaling equation $m={f}_{\ifmmode\pm\else\textpm\fi{}}h$, where $m$ and $h$ are normalized magnetization and field, respectively. The reliability of the critical exponents were confirmed by Widom scaling hypothesis $\ensuremath{\delta}=\ensuremath{\gamma}{\ensuremath{\beta}}^{\ensuremath{-}1}$. Apart from the slight increase in $\ensuremath{\beta}$ and $\ensuremath{\gamma}$, the deduced critical exponents were consistent with the theoretical prediction of the mean-field model, indicating the long range magnetic interaction in $\mathrm{Co}{}_{2}\mathrm{TiSn}$. Additionally, it is obtained that spin interaction decays as $J(r)\ensuremath{\sim}{r}^{\ensuremath{-}4.7}$. We suggest that the competition between localized majority spins and itinerant minority spins magnetic interaction could be responsible for critical behavior in $\mathrm{Co}{}_{2}\mathrm{TiSn}$.

Single-crystalline FeTe

Wide-range optical thermal sensing is achieved here based on the two-photon upconversion luminescence of the high-temperature (HT) cubic phase NaYF

We systematically investigate the influence of high pressure on the electronic transport properties of layered ferromagnetic materials; in particular, those of ${\mathrm{Fe}}_{3}{\mathrm{GeTe}}_{2}$. Its crystal sustains a hexagonal phase under high pressures up to 25.9 GPa, while the Curie temperature decreases monotonously with the increasing pressure. By applying appropriate pressures, the experimentally measured anomalous Hall conductivity, ${\ensuremath{\sigma}}_{xy}^{A}$, can be efficiently controlled. Our theoretical study reveals that this finding can be attributed to the shift of the spin--orbit-coupling-induced splitting bands of Fe atoms. With loading compression, ${\ensuremath{\sigma}}_{xy}^{A}$ reaches its maximal value when the Fermi level lies inside the splitting bands and then attenuates when the splitting bands float above the Fermi level. Further compression leads to a prominent suppression of the magnetic moment, which is another physical cause of the decrease in ${\ensuremath{\sigma}}_{xy}^{A}$ at high pressure. These results indicate that the application of pressure is an effective approach in controlling the anomalous Hall conductivity of layered magnetic materials, which elucidates the physical mechanism of the large intrinsic anomalous Hall effect.

The effects of laser irradiation and high pressure on the phase transition of cubic phase antimony trioxide microcrystals have been investigated. In situ Raman spectroscopy was performed at high pressure up to 45 GPa in a diamond anvil cell. The results indicated that two pressure-induced isostructural phase transitions occurred at 4.5 GPa and 11.3 GPa and were independent of laser irradiation. The Sb2O3 sample started transforming into a high density amorphous phase at 25 GPa and completed at more than 35 GPa. After irradiation for 7 minutes by 514.5 nm laser with 8 mW, the required pressure of the complete phase transition reduced to 27 GPa. On releasing pressure to ambient pressure, the samples reverse partly to the cubic phase, which takes days for the complete transition. This transition duration was reduced to seconds after irradiation by laser. It was also found that the residual amorphous phase at ambient pressure was of low density and medium-range order, which was not similar to the one that was observed at more than 25 GPa. The mechanism of laser irradiation boosting up the process of phase transitions was studied. Combining the cut-off wavelength of laser irradiation and absorption spectra, the photothermal effect induced via laser irradiation was found to dominate phase transition.

In this paper, Eu3+-doped yttrium tungstate (Y2WO6) nanophosphors with different morphologies have been synthesized by a hydrothermal method with the assistance of cetyltrimethyl ammonium bromide. X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and photoluminescence spectroscopy (PL) were used to characterize the products. The pH value of the starting solution plays a crucial role in the structures and morphologies of the samples. When the precursors synthesized under alkaline condition are annealed at 1100 °C in the air, the pure monoclinic Y2WO6 phase can be obtained. The results of HRTEM and SAED are consistent with those of the XRD patterns, confirming the high crystallinity of the products. A detailed study of the optical properties, including the UV–Vis diffuse reflection spectra, the excitation and emission spectra, CIE coordinate, and color purity of Y2WO6:Eu3+ nanophosphors with different doping concentrations, are presented here. The critical distance R c and energy transfer mechanism for the concentration quenching of Eu3+ ions are discussed in detail. In addition, the decay time and the thermal stability of the samples have been also investigated elaborately. The PL properties of the as-synthesized materials indicate promising applications in UV-pumped red light-emitting diodes.

The structure and photoluminescence properties are investigated under high pressure and high temperature for pure orthorhombic and hexagonal EuF3 nanocrystals. Under hydrostatic compression, the hexagonal EuF3 remains stable at pressures up to 26 GPa. Under nonhydrostatic compression, a cyclic phase transition from hexagonal to orthorhombic and then back to hexagonal is observed for the first time. When loading uniaxial compression, the pure hexagonal EuF3 partly transforms to orthorhombic at 70 MPa, then the orthorhombic EuF3 transforms to hexagonal at about 3 GPa, and the transition is completed at about 10 GPa. The cyclic phase transition is also observed during the heating process; the hexagonal transforms to orthorhombic at 550 °C and then to hexagonal at 855 °C. The content phase diagrams are obtained under high pressure and at high temperature.

To develop potential phosphors used in ultraviolet (UV) based white light-emitting diodes (WLEDs), a novel red Na3.6Y1.8(PO4)3:Eu3+ (NYP:Eu3+) phosphor was successfully prepared by a solid-state method. Rietveld refinement analysis determined that NYP has a cubic unit cell with space group Pm-3m. The structural properties were analyzed in detail by employing X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive spectrometry. Scanning electron microscope (SEM) image revealed the irregular morphology of NYP:Eu3+ particles and elemental mapping verified that Eu3+ ions were uniformly distributed on Y3+ sites. Photoluminescence (PL) spectra exhibited strong red emission under the excitation of 394 nm and optimal Eu3+ doping concentration in the NYP host was determined to be 30 mol%. The critical distance was calculated to be about 13.954 A and dipole-dipole interaction was responsible for the concentration quenching mechanism. NYP:Eu3+ phosphor demonstrated high thermal stability with emission intensity at 424 K was 97.4% of that at 298 K. Moreover, by employing the title red, green (Ba,Sr)2SiO4:Eu2+, blue BaMgAl10O17:Eu2+ (BAM:Eu2+) phosphors and near UV (NUV) light-emitting diode chip, a WLED device was fabricated, which possessed excellent CIE chromaticity coordinates of (0.3351, 0.3499) and high color rendering index (Ra = 87.5).