Pressure-induced Redshift Research Articles

Effects of chemically induced cationic disturbance on Mn4+ luminescence in double perovskites - temperature and pressure experimental and computational studies

We show the opportunity for tuning of the spectral position of the Mn4+ red emission in the series of double perovskites, Ba2LaNbO6:Mn4+, Ba2La(Nb0.8,Zr0.1,W0.1)O6:Mn4+, and Ba2La(Zr0.5,W0.5)O6:Mn4+ with increasing chemically induced symmetry disturbance. Such a disorder appeared attractive to engineering phosphors for pressure sensors or horticultural applications, for instance. The goal of the present research, not yet systematically addressed in the literature, was to unveil the correlation between chemically induced controlled crystal lattice distortion and the luminescence of Mn4+. For this purpose, the luminescence of these phosphors was methodically investigated at different pressures and temperatures. A pressure-induced redshift of photoluminescent lines with the rate of − 4 cm−1/kbar was found within the 0–230 kbar range, and the emission peak moved from 685 to 740 nm then. Furthermore, the cationic disorder allowed tuning of the Mn4+ luminescence making it useful for horticultural applications with a better fit between the emission wavelength and the strong chlorophyll absorption in the deep red part of the spectrum. The Mn4+ energy levels were computationally determined using the exchange charge model of the crystal-field theory which allowed for a deeper understanding of the experimental results. We found a correlation between the introduced disorder of the cationic subsystem and the energy of the Mn4+ emitting 2Eg level (R-line) as well as its intensity. This research brought a deeper understanding of the Mn4+-activated phosphors and, in turn, provides tips for a prudent search of materials for advanced practical uses.

Study on the local compressibility of (MnF6)2− centres in KNaSiF6: Mn4+ red phosphor material by analysing its pressure-induced spectral line shifts

The local linear compressibility of (MnF6)2− centres in KNaSiF6: Mn4+ red phosphor material is estimated by analysing its pressure-induced R-line red-shift. The result is confirmed by calculating the pressure-induced E(4T2)-line blue-shift. The evaluated local linear compressibility of (MnF6)2− impurity centres is much smaller than the linear compressibility of host KNaSiF6 crystal as a whole obtained from the theoretical calculation. The causes (i.e., the local compressibility of impurity cluster being smaller than the corresponding host one, and the local compressibility of the corresponding host cluster being also smaller than the compressibility of whole crystal) about the difference between the local compressibility of (MnF6)2− impurity centre and the compressibility of whole host KNaSiF6 crystal are discussed.

Pressure-induced evolution of structure and electronic property of GeP

The monoclinic semiconductor GeP is a new class of Group IV–V layered material, and it shows attractive anisotropic optical and electronic properties. In this paper, we investigate the structural and electronic evolution of layered GeP under pressure, using in situ x-ray diffraction, Raman and infrared spectra, and the density functional theory. All characterization methods reveal that the pressure causes two obvious phase changes. One isostructural transition is observed around 6 GPa. Above 21 GPa, another crystalline-to-amorphous transformation is obtained. It is worth noting that the high-pressure amorphous state can be retained at ambient conditions after the pressure is released. In addition, the pressure-induced red-shift of absorbance edge suggests its bandgap decreases with pressure. This result indicates that pressure has a significant effect on GeP. Meanwhile, it also provides a method for obtaining amorphous GeP, which is of interest to the energy storage community as it is a potential anode material for lithium-ion batteries.

Unraveling the anomalous mechanoluminescence intensity change and pressure-induced red-shift for manganese-doped zinc sulfide

Mechanoluminescence (ML) has promising applications such as stress sensors and many other fields, which raises intensive research attention and enthusiasms in the past few decades. However, accurate characterizations of the ML process with high temporal and spectral resolution remain a considerable challenge for the current scientific community. Here, an advanced ML characterization system based on the dynamic diamond anvil cell (dDAC) is developed to achieve flexible modulations of ML performances. Upon compression, the ML spectra of manganese-doped zinc sulfide (ZnS:Mn) show a large red-shift (~45 nm) and a volcano-trend of the ML intensity, where the cumulative ML intensity is solely dependent on the pressure change. DFT calculations identify the coupling of Mn-doping and surface vacancies is playing a crucial role in contributing to the improvement of ML through the band offset. The suppression of the vacancies formation on the surface by the applied pressure over 4 GPa leads to the decreases of the ML intensity. This work provides a brand new ML color and intensity tuning strategy and offers a promising method to explore the ML mechanism.

Pressure-Induced Structural Evolution and Bandgap Optimization of Lead-Free Halide Double Perovskite (NH4)2SeBr6.

Lead‐free halide double perovskites (HDPs) are promising candidates for high‐performance solar cells because of their environmentally‐friendly property and chemical stability in air. The power conversion efficiency of HDPs‐based solar cells needs to be further improved before their commercialization in the market. It requires a thoughtful understanding of the correlation between their specific structure and property. Here, the structural and optical properties of an important HDP‐based (NH4)2SeBr6 are investigated under high pressure. A dramatic piezochromism is found with the increase in pressure. Optical absorption spectra reveal the pressure‐induced red‐shift in bandgap with two distinct anomalies at 6.57 and 11.18 GPa, and the energy tunability reaches 360 meV within 20.02 GPa. Combined with structural characterizations, Raman and infrared spectra, and theoretical calculations using density functional theory, results reveal that, the first anomaly is caused by the formation of a Br‐Br bond among the [SeBr6]2− octahedra, and the latter is attributed to a cubic‐to‐tetragonal phase transition. These results provide a clear correlation between the chemical bonding and optical properties of (NH4)2SeBr6. It is believed that the proposed strategy paves the way to optimize the optoelectronic properties of HDPs and further stimulate the development of next‐generation clear energy based on HDPs solar cells.

High pressure photoluminescence properties and structural stability of Eu doped AlN nanowires synthesized via a direct nitridation strategy

High-aspect-ratio Eu doped AlN (AlN:Eu) nanowires (NWs) were synthesized via direct nitridation strategy. The NWs exhibits a strong green emission of the 5d-4f transition under ultraviolet light excitation. Photoluminescence (PL) spectra and synchrotron angle-dispersive X-ray diffraction (ADXRD) for AlN:Eu NWs were performed under hydrostatic pressures up to above 30 GPa. The pressure-induced monotonic red-shift of emission band (dλ/dP ≈ 5.9 nm GPa−1), as well as changes in the emission band widths, have been correlated with pressure for visible-light optical pressure sensors. As the pressure reaches around 20 GPa, the phase transition of AlN:Eu NWs from the wurtzite to rocksalt was found by the appearance of a PL band and ADXRD peak. The enhancement of transition pressure and bulk modulus in AlN:Eu NWs as compared with other ions doped AlN is considered to be caused by co-dopants of Eu2+ and Eu3+ ions. This work provides an effective strategy for doping large-size rare-earth ions into wide band-gap nitride semiconductor, and demonstrates a straightforward pathway for tuning optical properties through pressure without modifying composition.

Optical spectroscopy on the photo-response in multiferroic BiFeO3 at high pressure

The pressure dependence of light-induced effects in single-crystalline BiFeO3 is studied by optical spectroscopy. At low pressures, we observe three light-induced absorption features with energies just below the two crystal-field excitations and the absorption onset, respectively. These absorption features were previously ascribed to excitons, possibly connected with the ultrafast photostriction effect in BiFeO3. The pressure-induced redshift of the absorption features follows the pressure dependence of the corresponding crystal-field excitations and absorption onset, suggesting the link between them. Above the structural phase transition at Pc1≈3.5GPa, the three absorption features disappear, suggesting their connection to the polar phase in BiFeO3. The pressure-induced disappearance of the photoinduced features is irreversible upon pressure release.

The elastic properties and piezochromism of polyimide films under high pressure

The elastic properties of a fully aromatic polyimide were measured for the first time by Brillouin scattering in a high-pressure diamond anvil cell. Its isothermal compressibility and pressure dependence of mechanical moduli (Ks, E, and G) were studied and determined up to 6.4 GPa. Further, piezochromic behavior of the polyimide film was observed and studied in detail by spectroscopic analysis. Pressure-induced red shift of the absorption edge and a hysteretic phenomenon were found, due to an enhancement of the van der Waals interaction upon decreasing the interchain distances and partially collapsing the free volume under extreme pressure. A comprehensive study of elastic properties and piezochromism behavior of polyimide film under high pressure will provide useful information for developing pressure sensitive coatings, pressure sensors, pressure resistance parts and components.

Role of the pressure transmitting medium on the pressure effects in DWCNTs

We present a high-pressure optical spectroscopy study on double-walled carbon nanotubes with 0.80 nm and 1.45 nm using nitrogen, argon, and alcohol-mixture as pressure transmitting medium (PTM). The pressure-induced redshift of the optical transitions in the outer tubes is very small below 10 GPa, demonstrating the enhanced mechanical stability due to the inner tube. An anomaly at the critical pressure 12 GPa signals the onset of the pressure-induced deformation of the tubular cross-sections. Using argon as PTM affects the results quantitatively: The value is lower and the absorption bands are broadened considerably. Furthermore, alcohol-mixture as PTM seems to destroy the tubes completely above 10 GPa due to its solidification. The results are compared with those for single-walled carbon nanotubes.

Role of the Pressure Transmitting Medium for the Pressure Effects in Single-Walled Carbon Nanotubes

We present the pressure-dependent infrared absorbance spectra of unoriented single-walled carbon nanotube films for pressures up to 8 GPa. Various pressure transmitting media (helium, argon, CsI, and alcohol mixture) were employed to verify the influence of the pressure medium on the observed pressure effects. For all pressure transmitting media, a pressure-induced redshift of the absorption bands is observed, with an anomaly at the critical pressure Pc = 2−3 GPa. This anomaly can be attributed to the circular-to-oval structural phase transition. The pressure transmitting medium only affects the results quantitatively, namely, the value of Pc and the broadening of the bands.

Infrared studies of magnetite under high pressure

The pressure-induced changes in the optical response of magnetite were studied by infrared reflectivity measurements at room temperature. The pressure-induced redshift of the pronounced midinfrared absorption band confirms the polaronic transport mechanism. The low-frequency conductivity increases and the phonon modes harden with increasing pressure. We discuss our results in terms of the proposed pressure-induced charge transfer among the different Fe sites.

Anharmonic OH vibrations in brucite: Small pressure-induced redshift in the range 0-22 GPa

The uncoupled anharmonic OH-stretching vibrational frequency for the layered mineral Mg(OH)2(brucite) has been calculated in the pressure range 0(DFT) calculations were performed, followed by quantum-mechanical vibrational energy calculations.The following findings emerged: (1) The calculated d with the experimental literature value [taken as the average between the Raman and IR-measured slopes for Mg(OH) much smaller than that of traditional H-bond correlation curves in the literature. (3) The main origin of the small d are pressed toward each other. (4) At high pressure, the OH with respect to the variation of the D quadrupole coupling constant is approximately –1 kHz/GPa. −22 GPa. Quantum-mechanical electronic structureν(OH)/dP slope is –4 cm–1/GPa, in agreement2]. (2) The calculated ν(OH) vs. R(O···O) correlation is linear and the slope isν/dP and dν/dR(O···O) slopes is the small electric field variation as the mineral layers− ions show some tendency to be tiltedc axis, and a larger tilt angle leads to a larger ν(OH) downshift. (5) The pressure variation of the D quadrupole coupling constant is approximately –1 kHz/GPa.

High-pressure and optical properties of lanthanum magnesium hexa-aluminate doped with Mn2+ (LMA:Mn2+) laser material

The effect of hydrostatic pressure on the emission spectra and fluorescence lifetime (τ) of Mn2+ in LaMgAl11O19 (LMA) crystals up to 101kbar has been studied at room temperature. From the position of the peak (4T1→6A1 transition) in the emission spectra, we estimated that the pressure induced red-shift. A variation, slowly decreasing, in the fluorescence lifetime (τ) values for 4T1→6A1 transition was observed. The pressure-induced red-shift and lifetime variation could be described by simple models. In the considered pressure range (0–101kbar), a good agreement between the experimental values and theoretically predicted values was obtained.

Pressure-Induced Red Shift and Broadening of the Qy Absorption of Main Light-Harvesting Antennae Chlorosomes from Green Photosynthetic Bacteria and Their Dependency upon Alkyl Substituents of the Composite Bacteriochlorophylls

When pressure was applied to the main light-harvesting apparatus (chlorosomes) isolated from several green photosynthetic bacteria (up to 128 MPa), the Qy-absorption band in an aqueous solution was shifted to longer wavelengths. The shift, deltav, was completely reversible for (de)compression and also showed a linear relation as a function of the applied pressure. The pressure-sensitivity in the deltav was dependent upon the bacterial species. The pressure coefficient, deltav/deltaP, was -565 to -535 cm(-1) GPa(-1) for the chlorosomes from several green sulfur bacteria (Chlorobium species), which have several bacteriochlorophyll(BChl) homologues at the 8- and 12-positions as the antenna pigments. In contrast, a smaller value (-445 cm(-1) GPa(-1)) was estimated for the chlorosomes from the green nonsulfur bacterium (Chloroflexus aurantiacus), which has a single homologue with 8-ethyl and 12-methyl groups. These results were confirmed by the similar pressure dependency of in vitro self-aggregates of isolated BChls-c having various alkyl substituents at the 8- and 12-positions. The present pressurization study enables us to discuss a physiological meaning of a variety of antenna pigments in green photosynthetic bacteria.

Prediction of pressure-induced redshift of f1→d(t2g)1 excitations in Cs2NaYCl6:Ce3+ and its connection with bond-length shortening

Quantum chemical calculations including embedding, scalar relativistic, and dynamic electron correlation effects on Cs(2)NaYCl(6):(CeCl(6))(3-) embedded clusters predict (i) redshifts of the f(1)-->d(t(2g))(1) transition with pressure and (ii) bond-length shortening upon f-->d(t(2g)) excitation. Both effects are found to be connected which suggests that new high-pressure spectroscopic experiments could reveal the sign of the bond-length change.

The effect of pressure on luminescence properties of Cr 3+ ions in LiSc(WO 4) 2 crystals—Part I: Pressure dependent emission lineshape

We report the results of high-pressure studies of spectral properties in Cr 3+-doped LiSc(WO 4) 2 crystals between ambient pressure and 260 kbar. The effect of pressure on the present system has led to a structural transformation for pressure 60–88 kbar and a low-field → high-field spectral transformation of the Cr 3+ emission for pressure 117–227 kbar. The pressure-induced spectral transformation provided the opportunity to distinguish two distinct Cr 3+ sites in the host lattice. We have attributed them to the Cr 3+ ions that occupy the Li + and Sc 3+ sites. For both sites we observed that energy of the 2E excited state of Cr 3+ was lower than 14,000 cm −1 and exhibited pressure-induced red shift of about −2.5 cm −1/kbar. We have also observed the large inhomogeneous broadening of the 4T 2→ 4A 2 and 2E→ 4A 2 emissions. We have completed a quantitative analysis of the relative emission intensities of the 2E→ 4A 2 and 4T 2→ 4A 2 transitions as a function of pressure and temperature to study the distribution of the crystal field and electron–phonon coupling of the Cr 3+ in the host lattice. As the result we have recovered a functions that describe the distribution of the energy of 4T 2 state and electron–lattice coupling ( S - 1 2 ) ℏ ω in considered material.

Effect of pressure on luminescence properties ofCe3+:Lu2S3

We report the effect of pressure on d→f luminescence properties of Ce 3 + :Lu 2 S 3 up to ∼300 kbar. We observed that the d→f luminescence upon compression exhibited a large redshift in energy and a strong quenching in intensity. The pressure-induced redshift was explained by an increased crystal-field strength and nephelauxetic effect. We attributed the pressure-induced quenching in the intensity to a pressure-induced crossing of the conduction band edge of Lu 2 S 3 and the emitting 5d state of Ce 3 + on the basis of temperature-dependent luminescence intensity measurements. A quantitative analysis of the temperature dependence at several pressures was completed and analyzed using a photoionization model. Excellent agreement of the model with the experimental results was found.

The effect of pressure on the bacteriochlorophyll a binding sites of the core antenna complex from Rhodospirillum rubrum.

In this paper we examine the effect of pressure on the absorption spectrum and binding site of the core antenna complex from the photosynthetic bacterium Rhodospirillum rubrum. Absorption spectra and Raman spectra in preresonance with the Qy transition of the bacteriochlorophyll a were studied at pressures up to 625 MPa. In agreement with previous work we observe a pressure-induced red shift and broadening of the absorption spectrum. We show that at these pressures the pigments within the protein matrix at room temperature experience little if any distortion, and the hydrogen-bonding network involving the C2 and C9 carbonyl groups of the pigment molecules are undisturbed. Having shown the lack of sensitivity to pressure of the binding site interactions, which are known to modulate the absorption spectrum, we feel that it is relatively safe to attribute the pressure-induced red shift broadly to solvatochromic effects and, in particular, to the modulation of the pigment-pigment interactions by the pressure. This paper represents the first vibrational study of photosynthetic complexes at high pressure and the first application of FT Raman spectroscopy to biological molecules at high pressure.

Effect of hydrostatic pressure on the fluorescence of indole derivatives

Effects of hydrostatic pressure on the fluorescence emission of L-tryptophan, N-acetyl-L-trytophanamide and indole were investigated. An increase in pressure ranging from 1 bar to 2.4 kbar results in reversible red-shifts of the emission of the three fluorophores. The pressure-induced redshift amounts to about 170 cm(-1) at 2.4 kbar, and appears related to changes in Stokes shift of the fluorophores caused by pressure effects on the dielectric constant and/or refractive index of the medium. As the pressure range investigated here is the range commonly used in studies of protein subunit association and/or folding, these observations raise the need for caution in interpreting pressure-induced spectral shifts. The significance of these observations to pressure studies of proteins is illustrated by investigation of pressure effects on human Cu,Zn Superoxide dismutase (SOD) and azurin fromPseudomonas aeruginosa. A reversible 170 cm(-1) red-shift of the emission of SOD was observed upon pressurization to 2.4 kbar. This might be interpreted as pressure-induced conformational changes of the protein. However, further studies using SOD that had been fully unfolded by guanidine hydrochloride, and fluorescence anisotropy measurements indicated that the observed red-shift was likely due to a direct effect of pressure on the fluorescence of the single tryptophan residue of SOD. Similar pressure-induced red-shifts were also observed for the buried tryptophan residue of azurin or for azurin that had been previously denatured by guanidine hydrochloride. These observations further suggest that the effective dielectric constant of the protein matrix is affected by pressure similarly to water.

High‐pressure Raman Scattering and Optical Absorption Study of β‐GeS2

AbstractWe have measured Raman scattering and optical absorption spectra of layered β‐GeS2 at pressures up to 15GPa. Frequency shifts of selected internal bond bending and stretching modes are discussed, and three external (rigid‐layer) modes are identified. Changes in the Raman spectra near 9 GPa clearly indicate a structural phase transition. The pressureinduced red shift of the optical absorption edge shows a change in slope at about the same pressure. Samples turn opaque near 15 GPa, indicating a second transition to a disordered phase. The pressureinduced phase changes are reversible.