Temperature-induced Red Shift Research Articles

An ultrafast optical sensor for simultaneous detection of NH3 temperature and concentration based on ultraviolet absorption spectral redshift combined with spectral reconstruction

As a renewable and carbon-free fuel with high energy density, ammonia (NH3) is a promising alternative to fossil fuels. Real-time detection of its temperature and concentration is significant in improving NH3 combustion efficiency. In this paper, we report an optical sensor, which enables simultaneous measurement of temperature and concentration of NH3. The key idea is to acquire the temperature of NH3 through absorption spectral redshift, and determine its concentration by building three-dimensional field map combined with spectral reconstruction. Firstly, we explain the generation mechanism of temperature-induced redshift in ultraviolet differential absorption spectrum based on energy level distribution theory. The relationship between spectral redshift and temperature is then established using spectral autocorrelation algorithm. Secondly, a spectral reconstruction method based on absorbed intensity mapping wavelength is proposed to ensure real-time detection of NH3. Finally, a three-dimensional field map between temperature, reconstruction slope, and concentration is constructed to achieve the detection. Results indicated that the mean relative error in temperature measurement was 1.04% and the mean absolute error in concentration detection was 0.26mg/m3 in air. Additionally, the NH3 sensor enabled long-term detection with a detection limit of 15.50μg/m2, demonstrating its potential to broaden the application of NH3 as a fuel.

High-β lasing in photonic-defect semiconductor-dielectric hybrid microresonators with embedded InGaAs quantum dots

We report an easy-to-fabricate microcavity design to produce optically pumped high-β quantum dot microlasers. Our cavity concept is based on a buried photonic-defect for tight lateral mode confinement in a quasi-planar microcavity system, which includes an upper dielectric distributed Bragg reflector (DBR) as a promising alternative to conventional III–V semiconductor DBRs. The cavities show distinct emission features with a characteristic photonic-defect size-dependent mode separation and Q-factors up to 17 000. Comprehensive investigations further reveal lasing operation with a systematic increase (decrease) of the β-factor (threshold pump power) with the number of mirror pairs in the upper dielectric DBR. Notably, due to the quasi-planar device geometry, the microlasers show high temperature stability, evidenced by the absence of temperature-induced redshift of emission energy and linewidth broadening typically observed for nano- and microlasers at high excitation powers. The device exhibits remarkable lasing performance, maintaining efficacy even under elevated temperatures of up to 260 K.

Structural, luminescence and thermometric properties of LaVO4:Ln3+ nanopowders (Ln = Dy and Sm)

Lanthanide-doped materials have been intensively studied for optical thermometry due to their unique luminescence properties. However, the engineering of high-resolution multimode nanopowders for high-sensitivity thermometry is still a big challenge. Here, we study the structural and luminescence properties of Dy3+- and Sm3+-doped LaVO4 concentration series to find the suitable candidates for possible application as a temperature sensor. The synthesized nanocrystalline phosphors have successfully demonstrated multimode thermal sensing in the wide temperature range based on the temperature-induced red shift of the charge transfer band. The proposed sensing strategies were compared in terms of thermal sensitivity and temperature resolution. The best thermometric performances of Sr = 2.07 % K−1 and ΔT = 0.2 K at room temperature were found for LaVO4:Sm3+ 2 at% sample. The studies testify that Ln3+-doped LaVO4 materials are promising in multimode high-sensitivity optical thermometry.

Explaining the temperature-induced shift of the V-O charge transfer band experimentally and design of single-excitation ratiometric optical thermometry.

Temperature-induced redshift of the V-O charge transfer band (CTB) is promising for designing high performance optical thermometry. The shift mechanism is considered as the thermal populations of high vibrational energy levels of the VO4 3- ground state. Direct experimental evidence for this, however, is still lacking. In this work, Tm3+-doped YVO4 with various doping concentrations was studied to achieve strong 1D2 emission of Tm3+. The temperature dependent CTB was studied at low temperatures to give direct evidence experimentally for the shift mechanism of the CTB using YVO4:20% Tm3+. It was found that the V-O CTB does not shift when the temperature is lower than a certain temperature (60 K), verifying the proposed shift mechanism experimentally. In addition, based on the temperature quenching of 1D2 emission of Tm3+ and the redshift of the CTB, single-excitation ratiometric thermometry was carried out using YVO4:30% Tm3+,6% Sm3+. High relative sensitivity was achieved with a maximal value reaching up to 3.86% K-1 at approximately 355 K.

Eu3+-based dual-excitation single-emission luminescent ratiometric thermometry.

Recently, single-band ratiometric (SBR) thermometry becomes a hot-spot in the research field of optical thermometry. Here we propose a new SBR thermometry by combining the temperature-induced red shift of charge transfer state (CTS) of W-O and Eu-O with the ground state absorption (GSA) and excited state absorption (ESA) of Eu3+. The emitting intensity of the 5D0-7F2 transition of Eu3+ is monitored under CTS, GSA and ESA excitations at different temperatures. It is found that the SBR thermometry, depending on the combination of [GSA + CTS] of Eu3+ doped calcium tungstate, has the highest relative sensitivity of 1.25% K-1 at 573 K, higher than conventional luminescent ratiometric thermometry such as the 2H11/2 and 4S3/2 thermally coupled states of Er3+.

Photoluminescence, optical transition properties and temperature-induced shift of charge transfer band and temperature sensing property of GdNbTiO6: Sm3+ phosphors

GdNbTiO6: Sm3+ phosphors with various Sm3+ concentrations were prepared via a high temperature solid-state reaction method. The crystal structure of the samples was characterized by means of X-ray diffraction (XRD) and the as-prepared samples were confirmed to be orthorhombic phase GdNbTiO6. Photoluminescence properties were investigated by measuring the concentration- and temperature-dependent photoluminescence spectra. Concentration-dependent luminescence quenching and luminescent thermal quenching behaviors were observed and they were respectively ascribed to the electric dipole-dipole interaction between Sm3+ ions and the cooperation of energy transfer and crossover process. The chromatic characteristics were found to be dependent on the excitation wavelength and Sm3+ concentration. In addition, temperature-induced redshift of charge transfer band of GdNbTiO6 host was found in temperature-dependent excitation spectra and the opposite variations of different excitation peaks were utilized for optical thermometry. Finally, the optical transition property was studied on the basis of the diffuse reflectance spectra and Judd-Ofelt (J-O) theory, meanwhile, its accuracy was evaluated by the result of emission spectra.

Design of opposite thermal behaviors in Tm3+/Eu3+ co-doped YVO4 for high-sensitivity optical thermometry.

Temperature-induced redshift of the V-O charge transfer band edge and the temperature quenching effect were combined for designing ratiometric optical thermometry. Following this approach, opposite thermal behaviors of Tm3+ and Eu3+ emissions were realized in the range of 300 to 380 K in Tm3+/Eu3+ co-doped YVO4. Applying the temperature dependent fluorescence intensity ratio of Eu3+ to Tm3+ as temperature readout, the maximal relative sensitivity reaches up to 4.6%K-1 around 330 K. This result makes our proposed strategy an excellent candidate for developing high-sensitivity optical thermometry.

High-sensitive optical temperature sensing based on 5D1 emission of Eu3+ in YVO4

By studying the temperature-induced red-shift of the VO charge transfer band (CTB) edge in YVO4:10% Eu3+, we demonstrate a high-sensitive strategy for optical temperature sensing using the combination of the temperature-induced enhancement of the excitation in the tail of the CTB and the thermal population of 5D1 state of Eu3+. Under a constant 358 nm excitation, the integrated emission intensity corresponding to 5D1 → 7F1 transition of Eu3+ exhibits drastic temperature dependence ranging from 300 to 480 K. A high relative sensitivity SR was obtained to be 3923/T2. Temperature cycling tests were performed to evaluate the reusability and feasibility as temperature sensors. Our results indicate the potential use of the proposed strategy for high performance optical thermometry.

Optical thermometry based on cooperation of temperature-induced shift of charge transfer band edge and thermal coupling.

A novel optical thermometry is put forward, based on the cooperation of temperature-induced red shift of the charge transfer band (CTB) edge of the vanadates and thermal population of the thermally coupled energy levels (TCELs). Particularly, temperature-dependent CTB of Sm3+ (Er3+) doped LuVO4 was investigated from 300 to 480 K. Then, under the excitation of 360 nm at which the excitation efficiency enhances with temperature due to the temperature induced red shift of the CTB edge, temperature-dependent emissions of the TCELs of Sm3+ and Er3+ were investigated. The results indicate that the emission from the upper-level in the TCELs exhibits a dramatic increase, along with the increase of temperature. High relative sensitivity of 4304/T2 was obtained, which is remarkably superior to the previous reported sensors, using the temperature-dependent fluorescence intensity ratio of TCELs. This suggests that the proposed strategy is a promising candidate for highly sensitive optical thermometry.

A novel strategy for thermometry based on the temperature-induced red shift of the charge transfer band edge.

We report a novel strategy for optical temperature sensing using the temperature-induced red shift of the charge transfer band (CTB) edge of the VO43- groups in GdVO4:5% Sm3+. Excitation spectra were recorded at a series of temperatures ranging from 300 to 480 K. It is demonstrated that an excitation intensity of around 360 nm corresponding to the tail of the CTB and an excitation intensity of 407.6 nm corresponding to the 6H5/2 → 4F7/2 transition of Sm3+ exhibit opposite temperature dependence. Based on this, the relative sensitivity was obtained to be 3313/T2 in our investigated temperature range, which is remarkable progress compared with the optical temperature sensors reported previously. We believe that this work broadens the pathway for the design of highly sensitive temperature sensing materials.

Origin of the temperature-induced redshift of the charge transfer band of GdVO4.

The charge transfer band (CTB) of the VO43- groups in vanadates shifts to longer wavelengths with increasing temperature. The origin of this temperature-induced redshift was explored by studying the temperature-dependent excitation and emission spectra of GdVO4 ranging from 300 to 480K. The influences of the thermal population and the decline of the charge transfer gap on the spectral shift were analyzed using the configurational coordinate diagram. We conclude that the thermal population of vibrational sublevels of the ground electronic energy level dominates the temperature-induced redshift of the CTB. Taking advantage of the redshift and the thermal quenching, a novel ratiometric temperature-sensing strategy was proposed. Drastic temperature dependence was achieved, indicating a promising candidate for an optical thermometer with high sensing performance.

Large temperature-induced red shift of G-band of functionalized graphene nanosheets synthesized from humic acid

For the first time, temperature dependence of the G-band frequency for the functionalized graphene nanosheets synthesized using humic acid as precursor has been investigated. The Raman measurements has been performed using the excitation wavelength 514.5 nm and in the temperature range 23–116 °C. The prepared samples showed a negative temperature coefficient as large as −0.087 ± 0.008 cm−1/°C. Relatively large red shift of the G-band has been observed as the substrate temperature increases which indicates the higher sensitivity of the G-band peak position when the temperature varies. Such behavior has been attributed to the large contribution of the thermal expansion due to the lower Young's modulus of the reduced humic acid. This finding is important and opens the door for new applications of reduced humic acid as low cost, environmentally friendly and scalable material.

Temperature Effects on the Surface Plasmon Resonance in Copper Nanoparticles

The temperature dependences of the energy and the width of a surface plasmon resonance are studied for copper nanoparticles 17–59 nm in size in the silica host matrix in the temperature interval 293–460 K. An increase of the temperature leads to the red shift and the broadening of the surface plasmon resonance in Cu nanoparticles. The obtained dependences are analyzed within the framework of a theoretical model considering the thermal expansion of a nanoparticle, the electron-phonon scattering in a nanoparticle, and the temperature dependence of the dielectric permittivity of the host matrix. The thermal expansion is shown to be the main mechanism responsible for the temperature-induced red shift of the surface plasmon resonance in copper nanoparticles. The thermal volume expansion coefficient for Cu nanoparticles is found to be size-independent in the studied size range. Meanwhile, the increase of the electron-phonon scattering rate with the temperature is shown to be the dominant mechanism of the surface plasmon resonance broadening in copper nanoparticles.

Heterogeneity in Binary Mixtures of (Water + Tertiary Butanol): Temperature Dependence Across Mixture Composition

The temperature dependence of solution heterogeneity in binary mixtures of water and tertiary butanol (TBA) and its effects on a chemical reaction have been investigated by using steady-state and time-resolved spectroscopic experiments within the temperature range of 278 ≤ T/K ≤ 373. Eleven different mole fractions of TBA, covering extremely low TBA mole fractions to pure TBA, have been considered. An organic chromophore that undergoes a photoexcited intramolecular charge-transfer reaction is employed to reveal the signature of the solution heterogeneity. Upon increasing the solution temperature, the absorption spectrum of the dissolved chromophore exhibits a red shift at very low TBA concentrations but shifts toward higher energy (blue shift) at higher alcohol concentrations. This is a reflection of temperature-assisted aggregation of TBA molecules in very dilute aqueous solutions. The magnitude of the temperature-induced red shift is the largest at around 0.04 mol fraction of TBA, and a larger variation of the spectral line width across the temperature suggests enhanced solution heterogeneity. Reaction time constants measured at various mixture compositions are found to follow an Arrhenius-type temperature dependence. The average activation energy, when plotted as a function of mixture composition, steeply rises with TBA concentration in the limit of the very low TBA mole fraction and then suddenly levels off to a plateau upon further addition of TBA. The alcohol concentration-dependent activation energy abruptly changes its slope at a TBA mole fraction ∼0.1, at which a transition from the three-dimensional water-type network to the zigzag alcohol chain structure is known to occur. The plateau value of the activation energy is ∼6k(B)T and agrees well with the earlier estimate for the same chromophore from the pure solvent data at room temperature. The observed increase in the spectral red shift with temperature at low TBA mole fractions is in general agreement with the existing experimental results which support the view that temperature assists the aggregation of TBA molecules in dilute aqueous solutions of TBA. However, unlike in the small-angle neutron scattering study [ Bowron, D. T.; Finney, J. L. J. Phys. Chem. B 2007, 111, 9838], which finds clustering of TBA molecules reaching a maximum at ∼353 K, the present data do not indicate any such temperature maximum within the temperature range of 278 ≤ T/K ≤ 373.

Temperature Dependent Optical Response of Si(100): Theory vs. Experiment

ABSTRACTWe investigate theoretically and experimentally the temperature-dependent linear optical properties of the clean c(4×2) reconstructed Si(100) surface for a wide range of temperatures. We combine two theoretical formalisms: the first one incorporates the contribution of temperature-dependent atomic motion to the surface optical response and, the second uses a dielectric function layer-by-layer separation method. Using these formalisms, we model temperature-dependent reflectance anisotropy (RA) of this surface for the first time: finite temperature ab-initio Car-Parrinello Molecular Dynamics (CPMD) at different temperatures up to 1000 K provide temperature-dependent atomic structural inputs for optical calculations and subsequent average of dielectric functions. Experimentally, one-domain c(4x2) Si(100) surface was prepared and characterised by Reflectance Anisotropy Spectroscopy (RAS) in a temperature range between 300 K and 800 K. Good agreement between experiment and theory is demonstrated, including a temperature-induced red shift of both the surface and bulk optical peaks. Theoretical results indicate that the temperature-induced modification of the optical response is substantially more pronounced for the surface than for the bulk.

Theory of enhanced dynamical photo-thermal bi-stability effects in cuprous oxide/organic hybrid heterostructure

We theoretically demonstrate the formation of multiple bi-stability regions in the temperature pattern on the interface between a cuprous oxide quantum well and DCM2:CA:PS organic compound. The Frenkel molecular exciton of the DCM2 is brought into resonance with the 1 S quadrupole Wannier–Mott exciton in the cuprous oxide by “solvatochromism” with CA. The resulting hybrid is thermalized with the surrounding helium bath. This leads to strongly non-linear temperature dependence of the laser field detuning from the quadrupole exciton energy band which is associated with the temperature-induced red shift of the Wannier exciton energy. A numerical up- and down-scan for the detuning reveals hysteresis-like temperature distribution. The obtained multiple bi-stability regions are at least three orders of magnitude bigger (meV) than the experimentally observed bi-stability in bulk cuprous oxide (μeV ). The effective absorption curve exhibits highly asymmetrical behavior for the Frenkel-like (above the 1 S energy) and Wannier-like (below the 1 S energy) branches of the hybrid.

Carrier thermalization and activation within self-assembled InAs/AlAs quantum dot states

The carrier transfer and activation processes among lateral coupled InAs/AlAs quantum dots (QDs) are investigated based on the analysis of excitation power and temperature dependence of photoluminescence. An unusual red-shift of ground-state emissions, accompanied by a shrinkage of its line width, with increasing power density, is observed. It is explained by scattering and tunnelling of carriers, which result in a preferential capture of carriers into lateral coupled QDs and recombination from the lowest energy levels. The temperature-induced red-shift of the photon emissions from ground and excited states are attributed to the thermal activation and redistribution among these QD states.

Characterization of the primary photointermediates of Drosophila rhodopsin.

Invertebrate opsins are unique among the visual pigments because the light-activated conformation, metarhodopsin, is stable following exposure to light in vivo. Recovery of the light-activated pigment to the dark conformation (or resting state) occurs either thermally or photochemically. There is no evidence to suggest that the chromophore becomes detached from the protein during any stage in the formation or recovery processes. Biochemical and structural studies of invertebrate opsins have been limited by the inability to express and purify rhodopsins for structure-function studies. In this study, we used Drosophila to produce an epitope-tagged opsin, Rh1-1D4, in quantities suitable for spectroscopic and photochemical characterization. When expressed in Drosophila, Rh1-1D4 is localized to the rhabdomere membranes, has the same spectral properties in vivo as wild-type Rh1, and activates the phototransduction cascade in a normal manner. Purified Rh1-1D4 visual pigment has an absorption maximum of the dark-adapted state of 474 nm, while the metarhodopsin absorption maximum is 572 nm. However, the metarhodopsin state is not stable as purified in dodecyl maltoside but decays with kinetics that require a double-exponential fit having lifetimes of 280 and 2700 s. We investigated the primary properties of the pigment at low temperature. At 70 K, the pigment undergoes a temperature-induced red shift to 486 nm. Upon illumination with 435 nm light, a photostationary state mixture is formed consisting of bathorhodopsin (lambda(max) = 545 nm) and isorhodopsin (lambda(max) = 462 nm). We also compared the spectroscopic and photochemical properties of this pigment with other vertebrate pigments. We conclude that the binding site of Drosophila rhodopsin is similar to that of bovine rhodopsin and is characterized by a protonated Schiff base chromophore stabilized via a single negatively charged counterion.

Energy shifts of indirect excitons in coupled quantum wells

We review the various energy shifts which can be induced in a two-dimensional coupled quantum well structure. These include an electric field-induced red shift, a strain-induced red or blue shift, a density-induced blue shift, a temperature-induced red shift, and a magnetic field-induced red shift. We have seen several surprising effects, including a very large density-dependent blue shift and a very large red shift with magnetic field.

Relaxation mechanisms of electronic excitation in nanostructures of porous silicon

The temperature dependence of porous silicon (PS) photoluminescence and the dependence of the contact potential difference (CPD) in the dark after illumination on the photon energy were investigated for as-anodized PS and for PS oxidized in air for various times after anodization and HF treatment. The effect of the temperature-induced red shift (with decreasing temperature) decreases with increasing HF treatment time and is discussed under the assumption of different lifetimes for radiative and non-radiative recombination. Various photon energy thresholds could be observed by CPD, indicating the role of charge carrier injection in the PS properties.