Temperature-dependent Decay Research Articles

Reversible thermochromism, two-way mechanofluorochromism and tunable wavelength mechanoluminescence on tetraarylimidazole polymorphs

1, 2, 4, 5-tetraarylimidazole with 4-dimethylaminobiphenyl and 4-cyanophenyl (IMP) respectively introduced at N1 and C2 atom on imidazole core is prepared and two polymorphs correspondingly emit blue (IMP-B) and green (IMP-G) fluorescence are obtained by slow volatilization from solution. The solution-state emission displays the heavily solvatochromic effect as well as the unique solvent- and temperature-dependent LE, ICT and TICT emission equilibrium. X-ray crystallographic analysis, theoretic calculations and temperature-dependent emission decay spectra consistently support the assumption that the emission of IMP-B and IMP-G should respectively originate from LE and TICT state in.crystalline phase. For IMP-G crystal, it displays a reversible theromochromism by annealing-cooling cycles. Under force stimuli, IMP-B and IMP-G crystals present red- and blue-shifted MFC activity. The ground sample selectively pass through the two different routes to be recovered into the original crystalline phase, including transformation into IMP-B by annealing and into IMP-G by vapor fumigation. In spite of centrosymmetric space groups in both crystals, they still exhibit bright ML emission whose wavelength is nearly identical to that of fluorescence on each crystal. It is deduced that polar couples packed by molecules in two crystals may well account for the ML effect on the double polymorphs.

Nonlinear Temperature-Dependent Phonon Decay in Heavily Doped Silicon: Predominant Interferon-Mediated Cold Phonon Annihilation.

A nonlinear Fano interaction has been reported here which is manifest in terms of a parabolic temperature-dependent phonon decay process observable in terms of a Raman spectral parameter. Temperature-dependent Raman spectroscopic studies have been carried out on heavily and moderately doped crystalline silicon to investigate the behavior of anharmonic phonon decay in semiconductor systems where Fano interactions are present inherently. Systematic study reveals that in heavily doped systems an interferon-mediated decay route exists for cold phonons present at lower temperatures (<475 K) where Fano coupling is stronger and dominates over the typical multiple-phonon decay process. On the other hand, the anharmonic phonon decay remains the predominant process at higher temperatures irrespective of the doping level. Temperature-dependent phonon self-energy has been calculated using experimentally observed Raman line-shape parameters to validate the fact that the nonlinear decay of phonons through interferon mediation is a thermodynamically favorable process at low temperatures.

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe 2 Co} Coordination Polymers via Metal-to-Metal Charge Transfer

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe ₂ Co} Coordination Polymers via Metal-to-Metal Charge Transfer

Realizing External Quantum Efficiency over 25% with Low Efficiency Roll-Off in Polymer-Based Light-Emitting Diodes Synergistically Utilizing Intramolecular Sensitization and Bipolar Thermally Activated Delayed Fluorescence Monomer

Realizing External Quantum Efficiency over 25% with Low Efficiency Roll-Off in Polymer-Based Light-Emitting Diodes Synergistically Utilizing Intramolecular Sensitization and Bipolar Thermally Activated Delayed Fluorescence Monomer

Tailoring of strong orange-red-emitting materials for luminescence lifetime thermometry, anti-counterfeiting, and solid-state lighting applications

Strong orange-red-emitting Ba2LaTaO6:Eu3+ phosphors were designed and applied in various optical applications of luminescence lifetime thermometer, anti-counterfeiting film, and solid-state lighting applications. The crystal structure, elemental composition, asymmetry ratio, and other luminescent behaviors were investigated in detail. Especially, the optimal Ba2LaTaO6:0.1Eu3+ phosphor presented remarkable quantum yield (45.29%) and thermal stability (71.52% at 423 K). Based on the temperature-dependent luminescence decay curves, the maximum relative sensing sensitivity was 0.185 × 10−2 K−1 at 513 K. In addition, a novel anti-counterfeiting technique was introduced. The fabricated polydimethylsiloxane films exhibited three different colors under the irradiations of room light, 254 nm light, and 365 nm light, respectively. Eventually, the packaged light-emitting diode displayed the pure orange-red emission. Briefly, a series of the Eu3+-activated Ba2LaTaO6 phosphors with excellent luminescent properties were characterized and further applied in several optical fields for the first time.

Temperature quenching of Cr3+ in ASc(Si1-xGex)2O6 (A=Li/Na) solid solutions

Blue absorbing near infrared (NIR) emitting phosphors are a promising class of materials for phosphor converted NIR LEDs, which can be used in compact NIR spectrometers. Preferably, these phosphors have a broad emission spectrum and show negligible luminescence quenching at LED operating temperatures (100 °C). Here, we investigated ASc(Si1-xGex)2O6 (A = Li/Na, x = 0,0.2,0.4,0.6,0.8,1) solid solutions doped with Cr3+ to tune and optimize the emission maximum and bandwidth to cover the full 700–1100 nm range. With increasing Ge content an emission redshift was observed, along with emission band broadening at intermediate Ge/Si ratio, which is explained by disorder around Cr3+ in the second coordination sphere (mixed Si/Ge). Temperature dependent emission spectra and luminescence decay curves were measured between 90 K and 670 K to determine the quenching temperature TQ. With increasing Ge content TQ drops from 550 K to below 400 K. Interestingly, Cr3+ emission in the highly symmetric site in LiScSi2O6 shows a strongly temperature dependent lifetime before thermal quenching sets in. DFT calculations on LiScSi2O6 indicate that asymmetric vibrations at the Sc site are involved and calculated phonon energies were confirmed by measuring FTIR. Our study indicates that a solid solution is a promising way to increase the emission bandwidth. However, with increasing Ge content TQ decreases. An optimum Ge-content in LiSc(Si1-xGex)2O6:Cr3+ is x = 0.2–0.4 as it redshifts the NIR band maximum close to 900 nm and offers a FWHM bandwidth around 180 nm, while keeping the thermal quenching temperature high enough for application in NIR-LEDs.

Cryogenic Scintillation Performance of Cs4PbI6 Perovskite Single Crystals.

All-inorganic Cs4PbI6 single crystals (SCs) is emerging scintillators for radiation detection. In this study, we report on the X-ray scintillation properties of Cs4PbI6 SCs at the temperature range of 50-290 K. The temperature-dependent radioluminescence (RL) spectrum and decay time were investigated. It was found that the RL spectra show very pronounced temperature-dependent changes in the overall shape. The RL intensity increases with a decrease in the temperature under X-ray excitation. The emission bands at 318, 360, and 554 nm are attributed to the near-band-edge emission in Cs4PbI6 SCs, the 3P1 → 1S0 transition of the Pb2+ ion, and the emission of δ-CsPbI3 aggregates dispersed in the Cs4PbI6 SC matrix, respectively. With decreasing temperature, the fast and slow decay times tend to slow down and are estimated to be 46.0 ns (33.22%) and 820 ns (66.78%) at 50 K, which are far superior to that of the common cryogenic scintillator. These cryogenic scintillation characteristics of Cs4PbI6 SCs demonstrate its potential for cryogenic detection.

Experimental Measurement of Out-of-Time-Ordered Correlators at Finite Temperature.

Out-of-time-ordered correlators (OTOCs) are a key observable in a wide range of interconnected fields including many-body physics, quantum information science, and quantum gravity. Measuring OTOCs using near-term quantum simulators will extend our ability to explore fundamental aspects of these fields and the subtle connections between them. Here, we demonstrate an experimental method to measure OTOCs at finite temperatures and use the method to study their temperature dependence. These measurements are performed on a digital quantum computer running a simulation of the transverse field Ising model. Our flexible method, based on the creation of a thermofield double state, can be extended to other models and enables us to probe the OTOC's temperature-dependent decay rate. Measuring this decay rate opens up the possibility of testing the fundamental temperature-dependent bounds on quantum information scrambling.

Zinc Donor–Acceptor Schiff Base Complexes as Thermally Activated Delayed Fluorescence Emitters

Four new zinc(II) Schiff base complexes with carbazole electron donor units and either a 2,3-pyrazinedicarbonitrile or a phthalonitrile acceptor unit were synthesized. The donor units are equipped with two bulky 2-ethylhexyl alkyl chains to increase the solubility of the complexes in organic solvents. Furthermore, the effect of an additional phenyl linker between donor and acceptor unit on the photophysical properties was investigated. Apart from prompt fluorescence, the Schiff base complexes show thermally activated delayed fluorescence (TADF) with quantum yields up to 47%. The dyes bearing a phthalonitrile acceptor emit in the green–yellow part of the electromagnetic spectrum and those with the stronger 2,3-pyrazinedicarbonitrile acceptor—in the orange–red part of the spectrum. The emission quantum yields decrease upon substitution of phthalonitrile with 2,3-pyrazinedicarbonitrile and upon introduction of the phenyl spacer. The TADF decay times vary between 130 µs and 3.5 ms at ambient temperature. The weaker phthalonitrile acceptor and the additional phenyl linker favor longer TADF decay times. All the complexes show highly temperature-dependent TADF decay time (temperature coefficients above −3%/K at ambient conditions) which makes them potentially suitable for application as molecular thermometers. Immobilized into cell-penetrating RL-100 nanoparticles, the best representative shows temperature coefficients of −5.4%/K at 25 °C that makes the material interesting for further application in intracellular imaging.

Investigation on the optical sensing behaviors in single Eu3+-activated Sr2InSbO6 phosphors under green light excitation

The sensing sensitivities of the Sr2InSbO6:Eu3+ phosphors with different doping concentrations were investigated based on the temperature-dependent decay curves. The crystal and electronic structure were studied by the X-ray diffractometer (XRD), Rietveld refinement, and X-ray photoelectron spectroscopy (XPS). In addition, the luminescent behaviors (e.g., photoluminescence spectra, concentration quenching, thermal stability, and luminescent dynamic) were investigated under the green light excitation (λex = 529 nm). The dominated peak was assigned to the 5D0 → 7F1 transition emitting an orange-red emission. Moreover, the obtained sample exhibited excellent thermal stability that the emission intensity remained 91.61% at 425 K. Eventually, the relative sensing sensitivity of the Sr2EuSbO6 phosphor was 0.766% K−1 and the doping concentration of Eu3+ ions greatly affected the sensing sensitivity. This work is the first time to investigate the single Eu3+-activated luminescent materials under the green light excitation.

Effects of temperature-dependent burn-in decay on the performance of triple cation mixed halide perovskite solar cells

The understanding of the degradation mechanisms in perovskite solar cells (PSCs) is important as they tend to degrade faster under exposure to heat and light conditions. This paper examines the temperature-dependent degradation of solution processed triple-cation mixed halide PSCs (Cs0.05(FA0.95MA0.05)0.95Pb(I0.9Br0.05)3). The PSCs were subjected to temperatures between 30 and 60 °C for 3 h (180 min) to evaluate their current–voltage performance characteristics. Temperature-induced changes in the layer and interfacial structure were also elucidated by scanning electron microscopy (SEM). Our results show that thermally induced degradation leads gradually to the burn-in decay of photocurrent density, which results in a rapid reduction in power conversion efficiency. The SEM images reveal thermally induced delamination and microvoid formation between the layers. The underlying degradation in the solar cell performance characteristics is associated with the formation of these defects (interfacial cracks and microvoids) during the controlled heating of the mixed halide perovskite cells. The electrochemical impedance spectroscopy analysis of the PSCs suggests that the device charge transport resistance and the interfacial capacitance associated with charge accumulation at the interfaces both increase with extended exposure to light.

Temperature dependent perylene fluorescence as a probe of local polymer glass transition dynamics.

We demonstrate how the temperature dependence of perylene's fluorescence emission spectrum doped in bulk polymer matrices is sensitive to the local glass transition dynamics of the surrounding polymer segments. Focusing on the first fluorescence peak, we show that the intensity ratio IRatio(T) = IPeak(T)/ISRR between the first peak and a self referencing region (SRR) has a temperature dependence resulting from the temperature-dependent nonradiative decay pathway of the excited perylene dye that is influenced by its intermolecular collisions with the surrounding polymers segments. For different polymer matrices, poly(methyl methacrylate) (PMMA), polystyrene (PS), poly(2-vinyl pyridine) (P2VP), and polycarbonate (PC), we demonstrate that IRatio(T) exhibits a transition from a non-Arrhenius behavior above the glass transition temperature Tg of the polymer to an Arrhenius temperature dependence with constant activation energy E below the Tg of the polymer matrix, indicating perylene's sensitivity to cooperative α-relaxation dynamics of the polymer matrix. This transition in temperature dependence allows us to identify a perylene defined local Tperyleneg of the surrounding polymer matrix that agrees well with the known Tg values of the polymers. We define a fluorescence intensity shift factor in analogy with the Williams-Landel-Ferry (WLF) equation and use literature WLF parameters for the polymer matrix to quantify the calibration factor cf needed to convert the fluorescence intensity ratio to the effective time scale ratio described by the conventional WLF shift factor. This work opens up a new characterization method that could be used to map the local dynamical response of the glass transition in nanoscale polymer materials using appropriate covalent attachment of perylene to polymer chains.

Temperature-dependent long persistent luminescence properties and trap distributions in Sr2MgAl22O36: Eu2+

Long persistent luminescence (LPL) materials can be released its stored energy by various temperature induced thermal disturbance for a period of time. However, the accelerated release of trapped carriers at higher temperatures inhibits the use of LPL materials in extreme environments. In this work, a series of blue-emitting LPL phosphors Sr2MgAl22O36: Eu2+ were prepared by high temperature solid phase reaction. The investigation of photoluminescence (PL) and LPL preliminary indicated that the optimal room-temperature LPL time is 80 s, and the depth of trap was about 0.84 eV and 1.078 eV. Analyses of temperature-dependent LPL decay curves and thermoluminescence (TL) spectra show that the LPL initial brightness and duration time increase first and then decrease with the increase of temperature, and the optimal temperature is 453 K. These findings ensure the application of the discovered LPL phosphors above room temperature, including optical information storage and anti-counterfeiting among others.

Designing ultra-highly efficient Mn2+-activated Zn2GeO4 green-emitting persistent phosphors toward versatile applications

Developing highly efficient green-emitting phosphors is very significant because human eyes are sensitive to green spectral region. Herein, Mn2+-activated Zn2GeO4 phosphors, which can emit bright green light with an ultrahigh internal quantum efficiency of 98.5%, were prepared by a solid-state reaction technology in ambient atmosphere. At 323 nm irradiation, the emission spectrum shows a narrow band centered at 534 nm, which is ascribed to the 4T1 → 6A1 transition of Mn2+, with a full width at half maxima of 49.5 nm. Through monitoring the temperature-dependent photoluminescence emission intensity and decay time of Mn2+, we explored the thermometric properties of the resultant compound and found maximum relative sensitivities of Zn2GeO4:0.02Mn2+ phosphor are 4.90% K−1 and 0.74% K−1, respectively. Furthermore, green afterglow phenomenon is observed in the designed phosphors, and its mechanism is verified by discussing the thermoluminescence. Because of the excellent luminescence behaviors, various multimode luminescent patterns for information encryption are designed, including anticounterfeiting and fingerprint identification. Furthermore, using the prepared Zn2GeO4:0.02Mn2+ as green-emitting components, a white-light-emitting diode with suitable color coordinates, high color rending index (>90), and low correlated color temperature (5,000–6,000 K) was fabricated. These results demonstrate that Mn2+-activated Zn2GeO4 phosphors are multifunctional green-emitting components for optical thermometry, anticounterfeiting, fingerprint detection, and solid-state lighting applications.

Novel persistent phosphors Eu2+ - doped Sr5SiO4Cl6 with codopants Cr3+ and Sc3+ in high temperature application

New cyan long persistent luminescence (LPL) phosphors Sr5SiO4Cl6:Eu2+, Cr3+/Sc3+ (SSC: Eu2+, Cr3+/Sc3+) have been prepared. The LPL behaviors of the SSC are greatly enhanced through incorporating Cr3+ and Sc3+ ions as trap centers. The fluorescence and phosphorescence spectra of SSC:Eu2+, Cr3+/Sc3+ both show an asymmetric wide emission band at 446 nm, which is attributed to the 4f65 d1→4f7 transitions of Eu2+ions in two different Sr2+ sites. The LPL of the SSC:0.03Eu2+, 0.03Cr3+ can remain 11760 s above the identifiable intensity level (0.32 mcd⋅m−2) after 10 min of excitation (for SSC:0.05Eu2+, 0.05Sc3+, 4080s). In addition, the temperature-dependent afterglow decay curves also show good afterglow initial brightness at 443 K for SSC:0.03Eu2+, 0.03Cr3+ (for SSC:0.05Eu2+, 0.05Sc3+, 343 K). This research provides new blue LPL phosphors with potential applications in high temperature environment.

Deciphering crystal structure and photophysical response of Bi3+ and Pr3+ co-doped Li3Gd3Te2O12 for lighting and ratiometric temperature sensing

Crystal structure and photophysical response of Bi3+ and Pr3+ co-doped Li3Gd3Te2O12 system was investigated for lighting and ratiometric temperature sensing applications. The double substitution at the dodecahedral site was confirmed via Rietveld refinement and Raman spectra analysis. Considering the full advantage of distinct and characteristic cyan and orange emissions of Bi3+ and Pr3+, the emission tunability towards white region was achieved by the proposed co-doping combination. The as-prepared Li3Gd3Te2O12: Bi3+, Pr3+ phosphor exhibited characteristic and enhanced emission of Pr3+ under the excitation of 297 nm. The activation energy of 0.29 eV was obtained for the co-doped matrix, exhibiting better thermal stability. Further, the temperature sensing properties were evaluated based on the temperature dependent photoluminescence emission and decay curves in the range 100–300 K. Notably, the as-prepared Li3Gd3Te2O12: Bi3+, Pr3+ phosphor showed a maximum relative sensitivity of 0.672% K−1, as based on decay curve method, indicating that the phosphor can act as a potential candidate for optical temperature sensing in the physiological range. These findings demonstrate the efficiency of new co-doping combination Bi3+-Pr3+ for designing multifunctional phosphors.

Abnormal reduction and luminescence properties of Sm2+-doped Sr5(PO4)3Cl prepared by solution combustion synthesis

Sm-doped Sr5(PO4)3Cl was prepared by a solution combustion synthesis in the air atmosphere. The pure hexagonal phases of the samples were confirmed via the XRD, Raman, and FT-IR measurements. The typical microrod shape of the products was also demonstrated by SEM, TEM, and HRTEM images. The spectral properties and lifetimes were applied to characterize the luminescence of the samples as-prepared and subsequently heated in the air atmosphere. The luminescence of as-prepared Sm-doped Sr5(PO4)3Cl contains a broad emission band and a group of narrow lines, which are ascribed to the radiative transitions of 4f5d→4f and 5D0→7FJ (J = 0, 1, 2) of Sm2+ ions, respectively. It indicates that the Sm3+ can be successfully reduced to Sm2+ ions in hexagonal Sr5(PO4)3Cl prepared by combustion synthesis. The temperature dependent luminescence spectra and decay curves of Sm2+ were measured in a very wide temperature region from 10 K to 300 K. The thermal quenching and activation energy of Sm2+ doped Sr5(PO4)3Cl were reported. The crystal field energy level diagram and excitation mechanism of Sm2+ ions-doped Sr5(PO4)3Cl were characterized by the high resolution luminescence at low temperature. The luminescence of Sm2+ in Sr5(PO4)3Cl shows a great dependence on heating temperature in the air atmosphere (50–700 °C). The heating treatments at the elevated temperature depress Sm2+ emission along with the appearance of Sm3+ ions. The temperature-induced changes in the modification of the spectral components could be applied as potential luminescence thermometry.

Ethylene glycol associated facile preparation and luminescent behaviors of RE (RE = Sm3+, Dy3+) ions activated NaLuF4 nanoparticles

To achieve high quality luminescent nanomaterials, we synthesized series of rare-earth (RE; RE = Sm3+, Dy3+) ions activated NaLuF4 nanoparticles via a facile synthetic technique at room temperature. The phase category, microstructure and luminescent behaviors of the resultant samples were detailedly investigated. Under a certain excitation wavelength, these prepared nanoparticles can emit glaring visible light and the emission intensities are determined to be sensitive to the doping content. The optimal doping concentration for Sm3+ and Dy3+ ions in the NaLuF4 host lattices are 1 and 3 mol%, respectively, and the involved concentration quenching mechanisms are all contributed by the electric dipole-dipole interaction. The synthesized nanoparticles exhibit splendid thermal stability and the activation energies of the NaLuF:0.01Sm3+ and NaLuF4:0.03Dy3+ nanoparticles are 0.16 and 0.17 eV, respectively. Furthermore, the temperature-dependent decay time reveals that the thermal quenching mechanism of the designed nanoparticles is responsible by the crossover process between the excited level and ground state. These results indicate that the resultant nanoparticles with good luminescent materials and high thermal stability are potential candidates for white light-emitting diode.

Temperature-dependent photoluminescence and decay times of different phases of grown TiO2 nanoparticles: Carrier dynamics and trap states

Three different phases, namely anatase, mixed and rutile phases of TiO2 nanoparticles (NPs) were developed with varying temperatures from 400 to 900 °C and confirmed using various characterization techniques. The XRD analysis of TiO2 NPs in temperature range of 290 to 77 K with no significant changes predict the thermally stable NPs. Photoinduced carrier dynamics of TiO2 NPs were investigated by the temperature dependence (TD) photoluminescence (PL) and TD time-resolved PL (TRPL) decays. With varying temperatures from 290 to 77 K, the anatase phase exhibits an additional and dominant 530 nm PL band. However, the mixed and rutile phases show three well-resolved PL bands, including 420 nm, 530 nm and near-infrared (NIR) bands at 820 nm at a lower temperature. Again, 530 nm band dominated for mixed-phase.In contrast, for the rutile phase, the 820 nm band dominated at <100 K. The PL lifetime of the 420 nm band is nearly a single exponential for all the phases. And is also true for the 530 and 820 nm PL bands, but bi-exponential for ≤100 K. Both the PL and TRPL results predict the presence of trap states in TiO2 NPs for anatase and rutile phases. The PL is originated due to donor-acceptor recombination, whereas oxygen vacancies served as donor and hydroxyl groups serve as accepter sites. The NIR band is attributed to the trapped electrons in rutile TiO2, which recombine with free holes and intrinsic defects. Also, the trapped electrons were generated in one of two ways: direct trapping or trap-to-trap hopping. The carrier dynamic in NPs depends on the trap states as the photoexcited carriers transfer into surface sites which competes with non-radiative and radiative recombinations during the relaxation process. Thus, the findings show that the trap states in TiO2 can significantly influence TiO2 photocatalytic activity when exposed to appropriate light.

Effective energy transfer from Dy3+ to Tb3+ ions in thermally stable KZABS glasses for intense green emitting device applications

Potassium Zinc Alumino Borosilicate (KZABS) glasses co-doped with Dy3+/Tb3+ ions have been synthesized by employing a sudden melt quenching technique. To check the luminescence behavior, the as prepared glasses were characterized by employing spectroscopic tools like photoluminescence (PL) excitation and emission, temperature dependent PL and PL decay to see the energy transfer between Dy3+ and Tb3+ ions and optimum green emission suitable for photonic applications. The XRD spectra reveals the amorphous nature of the as prepared KZABS glasses. PL spectral features show optimum green emission and confirms energy transfer from Dy3+ to Tb3+ ions. With the help of temperature dependent PL, glasses were found to be thermally stable. The decay profiles recorded show bi-exponential nature and demonstrates the energy transfer that took place from Dy3+ to Tb3+ ions. The Inokuti- Hirayama (I–H) model confirms the interaction involved in energy transfer process as dipole-dipole in nature. The CIE coordinates are found to be shifting gradually towards intense green region with increase in activator concentration (Tb3+) under the optimized sensitizer (Dy3+) concentration. It is also observed that, the CIE coordinates shifting towards intense green region when the as prepared KZABS glasses are excited with suitable excitation wavelengths of both sensitizer and activator. All the studies finally reveal the superiority of Dy3+/Tb3+ co-doped KZABS glasses for their usage in green emitting photonic device applications such as w-LEDs and display devices.