Temperature Dependence Of Energy Transfer Research Articles

Dopant effect on the optical and thermal properties of the 2D organic-inorganic hybrid perovskite (HDA)2PbBr4.

Lead-based two-dimensional organic-inorganic hybrid perovskites (2D HOIPs) are popular materials with various optical properties, which can be tuned through metal ion doping. Due to the size and valence misfit, metal ion dopants in 2D lead-based HOIPs are still limited. In this work, Mn2+, Sb3+ and Bi3+ are doped into 2D (HDA)2PbBr4 (HDA = protonated dopamine) successfully. As a result, the dopants in 2D (HDA)2PbBr4 can induce their characteristic optical spectra, which is studied at different temperatures and excitation powers. The temperature-dependent energy transfer in the Mn-doped sample has been clarified, in which abnormal phenomena including negative thermal quenching have been observed. In addition, the dopant ions can impact the phase transition temperatures of the samples, especially lowering their crystallization temperatures greatly. The mussel-inspired organic cation, feasible metal ion regulation, and superior stability provide (HDA)2PbBr4 potential for further applications.

Temperature dependent energy transfer to Eu3+ emission centres in K5Eu(MoO4)4 crystals

Luminescence properties of a palmierite-type K5Eu(MoO4)4 crystal were studied in a wide temperature range of 7–650 K.

Shallow trap mediated temperature-dependent exciton and Mn2+ photoluminescence in CsPbCl3:Mn2+ nanocrystals

As an effective means to endow lead halide perovskite nanocrystals (NCs) with new properties, ion doping has been widely applied. Transition metal Mn-doped CsPbCl3 is of particular interest, as the Mn doping introduces new emission bands, improves photoluminescence quantum yield (PLQY), and even enhances stability. However, it is still insufficient to catch insight of the energy transfer process and luminescence characteristics of these high defect tolerance NCs doped with Mn ion. Here, we systematically studied the energy transfer from exciton to Mn2+ ions in Mn-doped CsPbCl3 NCs by variable temperature steady-state fluorescence spectra and time-resolved spectra. The abnormal attenuation behavior of the exciton and Mn2+ with the change of temperature was observed, from which we predict the existence of shallow traps near the conduction band and these shallow traps will affect the luminescence properties by influencing the energy transfer process. We show a simple physical model invoking only shallow trap states that uniquely describe the temperature-dependent energy transfer between the exciton and the Mn2+ ion. The thermometric performance (30–290 K) was studied in terms of relative thermal sensitivity, in which the calculated relative sensitivity range is ∼0.12%–1% K−1.

Bright State Sensitized Triplet Energy Transfer from Quantum Dot to Molecular Acceptor Revealed by Temperature Dependent Energy Transfer Dynamics.

Quantum dot (QD) sensitized molecular triplet excited state generation has been a promising alternative for traditional triplet state harvesting schemes. However, the correlation between QD bright/dark states and QD sensitized triplet energy transfer (TET) has been unclear. Herein, we studied the bright/dark states contribution to TET with CdSe/CdS core/shell QD-oligothiophene as the model system. Equilibrium between QD bright and dark states was tuned by changing temperature, and TET dynamics were monitored with transient absorption spectroscopy. Analysis of acceptor triplet excited state growth kinetics yields rates of TET from bright and dark states as 0.492 ± 0.011 ns-1 and 0.0271 ± 0.0014 ns-1 at 5 K, suggesting significant contribution of bright states to TET. The result was rationalized by bright state wave function components with the same electron/hole spin projections leading to nonzero TET probability. The study provides new insights into QD sensitized TET mechanisms and inspiration for future TET efficiency optimization through QD exciton engineering.

Near-unity blue-orange dual-emitting Mn-doped perovskite nanocrystals with metal alloying for efficient white light-emitting diodes

The tunable dual-color emitting Mn2+ doped CsPbCl3-xBrx nanocrystals (NCs) with near-unity photoluminescence quantum yield (PL QY) were synthesized through post-treatment of metal bromide at room temperature for fabrication of efficient warm white light-emitting diodes (WLEDs). Especially, the CdBr2 treated blue-orange emitting Mn doped NCs with various Mn/Pb molar feed ratios exhibit higher PL QY of 97% and longer Mn2+ PL lifetime of 0.9 ms. It is surprisingly found that the X-ray diffraction peak at 31.9° is almost not changed with increasing Br composition, meaning formation of metal alloying due to incorporation of amount of divalent cation in NCs. The strong and stable Mn2+ PL at temperature ranging from 80 K to 360 K are revealed and the temperature-dependent energy transfer efficiencies in Mn2+ doped CsPbCl1.5Br1.5 NCs are obtained. The enhancement mechanism of Mn2+ PL QY was attributed to improved energy transfer from exciton to Mn2+ d–d transition and suppressed defect state density after post-treatment. The efficient warm WLEDs with color rendering index of 90 and luminous efficacy of 92 lm/W at 10 mA were fabricated by combining blue-orange dual-emitting Mn2+ doped CsPbCl3-xBrx@SiO2 and green emissive CsPbBr3@SiO2 NCs with violet GaN chips.

Enhancement of the Ln3+ ratiometric nanothermometers by sensitization with transition metal ions

• The transition metal ions were used for sensitization of lanthanide ions. • This strategy enables the enhancement of the thermal LIR changes. • An increase of relative sensitivity by 300% was observed after co-doping. One of the most important parameters that affect the thermal resolution in the luminescent thermometry is the relative sensitivity of phosphor to temperature changes. Therefore various approaches to enhance its value are intensively investigated. The strategy of the relative sensitivity enhancement of the ratiometric lanthanide ions based luminescent thermometer by the sensitization with the transition metal ions is proposed in this work. It was found that by taking advantage of the temperature dependent energy transfer from transition metal ion (Mn 4+ -, Cr 3+ - and Ti 3+/4+ -) to the Tb 3+ and Eu 3+ ions in the YAG powder, the thermal variation of the Tb 3+ to Eu 3+ luminescence intensity ratio increases leading to the improvement of its thermometric properties even by 300%. Therefore, the maximal relative sensitivity increases from S R = 0.09%/°C for unco-doped powder up to S R = 0.15, 0.28, 0.30%/°C, for powders co-doped with Cr 3+ , Mn 4+ and Ti 3+/4+ , respectively. The beneficial influence of the transition metal to lanthanides energy transfer was investigated in a function of the transition metal ion concentration.

Luminescence and up-conversion of single crystalline Lu3Al5O12:Pr3+

This work deals with the spectroscopic properties of praseodymium doped single crystalline lutetium aluminum garnet (LuAG:Pr3+). A special focus was set on temperature- and time-dependent spectroscopy. Beyond the well-known down-conversion luminescence of LuAG:Pr3+, also UV-A/B up-conversion luminescence under excitation with a 488 nm laser was thoroughly investigated. Furthermore, the results of the spectroscopic investigations on the single crystalline material were supplemented and compared with measurements on a microscale powder sample.In addition, to the spectroscopic investigations, mechanistic considerations are presented to obtain a closer look at the up-conversion process in LuAG:Pr3+. We promote the thesis of a temperature-dependent energy transfer up-conversion mechanism.

Wide-range and highly-sensitive optical thermometers based on the temperature-dependent energy transfer from Er to Nd in Er/Yb/Nd codoped NaYF4 upconversion nanocrystals

In this paper, we report the temperature-dependent energy transfer (ET) process between Er3+ and Nd3+ ions and optical temperature sensing properties based on the upconversion (UC) luminescence of Er3+ and Nd3+ in Er/Yb/Nd codoped NaYF4 nanocrystals synthesized via a hydrothermal method. The decrease of green and red UC emissions of Er3+ and the increase of infrared UC emissions of Nd3+ at elevated temperatures indicated an effective ET from the Er3+ to Nd3+ ions with increasing temperature, which was investigated both experimentally and theoretically. Based on the fluorescence intensity ratio technique, the optical temperature sensing behaviors from the thermally coupled (TC) energy levels (Er3+: 2H11/2/4S3/2 and Nd3+: 4F7/2/4F5/2/4F3/2) and inter-ion energy levels between 4F9/2 of Er3+ and 4F7/2/4F5/2/4F3/2 of Nd3+ were studied in the cryogenic region and high-temperature range. The sensing sensitivity of an optical thermal sensor based on the inter-ion energy levels between Er3+ and Nd3+ was as high as 0.83 K−1, which was an approximate increase of three orders of magnitude compared to that based on the TC energy levels of Er3 and Nd3+. It is anticipated that the Er3+/Nd3+ codoped phosphors could be used to construct wide-range and highly sensitive luminescent thermometers.

Exciton energy transfer in hybrid organics – Semiconductor nanostructure

We consider a hybrid heterostructure containing an inorganic quantum well in close proximity with an organic material as overlayer. The resonant optical pumping of Frenkel exciton can lead to an efficient indirect pumping of Wannier excitons. As organic material in such hybrid structure we consider crystalline tetracene. In tetracene diffusion length of singlet exciton diffusion is strongly dependent on temperature. We have obtained the exact analytical solution of diffusion equation for exciton in organics at different temperatures defining different diffusion lengths of excitons. Then we have included in consideration Coulomb interaction between organics and QW. It was shown that this interaction multiple increases effectiveness of transfer from organics to QW in the same way as it was predicted early in our publications for inverse transfer from QW to organics. The effectiveness of energy transfer in hybrid with tetracene was calculated by definite method for two selected temperatures that opens possibility to operate in full region of temperatures. Temperature dependence of energy transfer in organics opens a new possibility to turn on and off the indirect pumping due to energy transfer from the organic subsystem to the inorganic subsystem. This varying pumping may be used for experimental investigating of different nonlinear effects.

Temperature dependence of energy transfer between Nd3+ and Yb3+ ions in phosphate glass.

The temperature dependence of energy transfer between Nd3+ and Yb3+ ions in phosphate glass was investigated with emission spectra, time-resolved spectroscopy, and luminescence lifetimes. The time-resolved spectrograms vividly displayed processes of both Nd3+→Yb3+ energy transfer and Yb3+→Nd3+ energy transfer. The impact of temperature on energy transfer rate has been studied by analyzing the cumulative rise times and decay times of Yb3+ upon excitation of Nd3+ and the cumulative rise times and decay times of Nd3+ upon excitation of Yb3+ at different temperatures. It has been found that both Nd3+→Yb3+ energy transfer and Yb3+→Nd3+ energy transfer are accelerated along with increasing temperatures in a certain temperature range.

Concentration effect on up-conversion luminescence and excitation path-dependent luminescence temperature quenching in YNbO4:Ho3+/Yb3+ phosphors.

Usually, the luminescence intensity and mechanism of rare-earth ions doped materials are dependent on both doping concentration and sample temperature. In this study, we attempt to explore the concentration effect on up-conversion (UC) luminescence and the dependence of luminescence temperature quenching on excitation wavelength in YNbO4: Ho3+/Yb3+ phosphors. The YNbO4: Ho3+/Yb3+ phosphors with various Ho3+ and Yb3+ concentrations were synthesized via a high-temperature solid-state reaction technique. Intense green UC emission peaked at 543 nm was observed, accompanying with weak red and near infrared (NIR) UC emissions centered at 659 and 745 nm. Based on the laser working current dependence of UC luminescence, two-photon processes were responsible for both the green and the red UC emissions under 980 nm excitation, which have no apparent dependence on both Ho3+ and Yb3+ concentrations. According to the Arrhenius model, crossover process was responsible for the temperature-dependent down-conversion (DC) luminescence quenching of Ho3+ under 452 nm excitation. However, the temperature quenching processes of the green and the red UC luminescence cannot be well explained by Arrhenius model. It was found that the UC luminescence intensity decayed with increasing sample temperature, which was caused by both the crossover and temperature-dependent energy transfer processes.

Temperature dependent energy transfer in Bi/Er codoped barium gallogermanate glasses for tunable and broadband NIR emission

A tunable and further broadened NIR emission can be realized in Bi/Er codoped barium gallogermanate glasses by tuning the Er3+content, the temperature and the pumping schemes.

Multicolor Tuning and Temperature-Triggered Anomalous Eu3+-Related Photoemission Enhancement via Interplay of Accelerated Energy Transfer and Release of Defect-Trapped Electrons in the Tb3+,Eu3+-Doped Strontium-Aluminum Chlorites.

So far, a large number of rare earth (RE) and non-RE-doped emission-tunable crystals based on controllable energy transfer have become available, but numerous mechanistic issues, particularly for those that involve temperature-dependent energy transfer between the well-shielded 4f RE ions, lack comprehensive theoretical and experimental investigation, limiting greatly their development and applications in the future. Here, we design and report a type of Tb3+,Eu3+-doped Sr3Al2O5Cl2 phosphors capable of multiemissions upon excitation at 376 nm, through using the orthorhombic Sr3Al2O5Cl2 as the host lattice while the well-shielded 4f Tb3+ and Eu3+ ions as dual luminescent centers. Our results reveal that the energy transfer from Tb3+ to Eu3+ ions, happening via an electric dipole-quadrupole (d-q) interaction, can be controlled by the doping ratio of Tb3+ and Eu3+, leading to the tunable emissions from green (0.3159, 0.5572) to red (0.6579, 0.3046). It is found from time-resolved photoluminescence (PL) spectra that this energy transfer begins at t = 5 μs and gradually ends at t ≥ 200 μs. Moreover, from temperature-dependent PL results, we reveal that the Eu3+ emission features an anomalous intensity enhancement at the earlier heating state. With the density functional theory (DFT) calculations, we have screened the possibilities of site preferential substitution problem. By jointly taking into account the X-ray diffraction Rietveld refinement, DFT findings, and PL and thermoluminescence spectra, a mechanistic profile is proposed for illustrating the PL observations. In particular, our discussions reveal that the temperature-triggered Eu3+ emission enhancement is due to the interplay of the temperature-induced accelerated energy transfer and defect-trapped electrons that are released upon the thermal stimulation. Unlike most of reported phosphor materials that are always suggested for phosphor-converted white light-emitting diodes, we propose new application possibilities for Tb3+,Eu3+-doped Sr3Al2O5Cl2 phosphors, such as anticounterfeiting, temperature-controlled fluorescence sensor, data storage, and security devices.

Ultrafast multi-pulse transient absorption spectroscopy of fucoxanthin chlorophyll a protein from Phaeodactylum tricornutum

We have applied femtosecond transient absorption spectroscopy in pump-probe and pump-dump-probe regimes to study energy transfer between fucoxanthin and Chl a in fucoxanthin-Chl a complex from the pennate diatom Phaeodactylum tricornutum. Experiments were carried out at room temperature and 77 K to reveal temperature dependence of energy transfer. At both temperatures, the ultrafast (<100 fs) energy transfer channel from the fucoxanthin S2 state is active and is complemented by the second pathway via the combined S1/ICT state. The S1/ICT-Chl a pathway has two channels, the fast one characterized by sub-picosecond energy transfer, and slow having time constants of 4.5 ps at room temperature and 6.6 ps at 77 K. The overall energy transfer via the S1/ICT is faster at 77 K, because the fast component gains amplitude upon lowering the temperature. The pump-dump-probe regime, with the dump pulse centered in the spectral region of ICT stimulated emission at 950 nm and applied at 2 ps after excitation, proved that the S1 and ICT states of fucoxanthin in FCP are individual, yet coupled entities. Analysis of the pump-dump-probe data suggested that the main energy donor in the slow S1/ICT-Chl a route is the S1 part of the S1/ICT potential surface.

Frederick Yi-Tung Cho (1939–2011)

We present here a Tribute to Frederick Yi-Tung Cho (1939-2011), an innovative and ingenious biophysicist and an entrepreneur. He was one of the 4 earliest PhD students [see: Cederstrand (1965)-Carl Nelson Cederstrand; coadvisor: Eugene Rabinowitch; Papageorgiou (1968)-George C. Papageorgiou (coauthor of this paper); and Munday (1968)-John C. Munday Jr. (also a coauthor of this paper)] of one of us (Govindjee) in Biophysics at the University of Illinois at Urbana-Champaign (UIUC) during the late 1960s (1963-1968). Fred was best known, in the photosynthesis circle for his pioneering work on low temperature (down to liquid helium temperature, 4K) absorption and fluorescence spectroscopy of photosynthetic systems; he showed temperature independence of excitation energy transfer from (i) chlorophyll (Chl) b to Chl a and (ii) from Chl a 670 to Chl a 678; and temperature dependence of energy transfer from the phycobilins to Chl a and from Chl a 678 to its suggested trap. After doing research in biophysics of photosynthesis, Fred shifted to do research in solid-state physics/engineering in the Government Electronics Division (Group) of the Motorola Company, Scottsdale, Arizona, from where he published research papers in that area and had several patents granted. We focus mainly on his days at the UIUC in context of the laboratory in which he worked. We also list some of his papers and most of his patents in engineering physics. His friends and colleagues have correctly described him as an innovator and an ingenious scientist of the highest order. On the personal side, he was a very easy-going and amiable individual.

Temperature tunable cascaded energy transfer during femtosecond nonlinear frequency conversion process

The paper reports a combined experimental and theoretical study of temperature dependent energy transfer process of second harmonic generation from a broadband ultrashort pulse by using the periodically poled lithium niobate crystal. It was found that a narrowband SH beam can be generated and the tuning of their central wavelength was realized by the temperature or the amount of the phase-mismatching of the nonlinear crystal under large group velocity mismatch. The experimental results were well fitted by the numerical simulations on the basis of the coupled equations for the cascaded nonlinear process. The investigation allow us to provide a promising method to achieve a narrow-band, dense and efficient multi-frequency device.

Double rare-earth nanothermometer in aqueous media: opening the third optical transparency window to temperature sensing.

Owing to the alluring possibility of contactless temperature probing with microscopic spatial resolution, photoluminescence nanothermometry at the nanoscale is rapidly advancing towards its successful application in biomedical sciences. The emergence of near-infrared nanothermometers has paved the way for temperature sensing at the deep tissue level. However, water dispersibility, adequate size at the nanoscale, and the capability to efficiently operate in the second and third biological optical transparency windows are the requirements that still have to be fulfilled in a single nanoprobe. In this work, these requirements are addressed by rare-earth doped nanoparticles with core/shell-architecture, dispersed in water, whose excitation and emission wavelengths conveniently fall within the biological optical transparency windows. Under heating-free 800 nm excitation, double nanothermometry is realized either with Ho3+-Nd3+ (1.18-1.34 μm) or Er3+-Nd3+ (1.55-1.34 μm) NIR emission band ratios, both displaying equal thermal sensitivities around 1.1% °C-1. It is further demonstrated that, along with the interionic energy transfer processes, the thermometric properties of these nanoparticles are also governed by the temperature dependent energy transfer to the surrounding solvent (water) molecules. Overall, this work presents a novel water dispersible double ratiometric nanothermometer operating in the second and third biological optical transparency windows. The temperature dependent particle-solvent interaction is also presented, which is critical for e.g. future in vivo applications.

Temperature Dependent Energy Transfer in Ce3+-Yb3+ Co-Doped YAG Phosphors

Ce3+-Yb3+ co-doped Y3Al5O12 (YAG) phosphors were prepared, and their photoluminescence spectra, photoluminescence excitation spectra and fluorescence decay curves were measured at different temperatures from 8 K to 300 K. Experimental results show that, besides thermal quenching effect, the energy transfer is also the mechanism for the temperature dependence of the Yb3+ emission. A photo-induced Ce-O-Yb charge transfer state model is proposed to explain the variation of the emission with the temperature. The decay curves of the co-doped YAG phosphors at different temperatures can also be explained by the model.

Investigation of the quenching mechanisms of Tb3+ doped scheelites

The luminescence of terbium-doped lead tungstate (PbWO4:Tb3+) features not only emission from the 5D4 and 5D3 excited states of Tb3+, but also host and defect related broad emission bands are found. The blue host emission is attributed to the WO42− centres whereas the green emission can be ascribed to WO3 defects. Upon host excitation, Tb3+ emission is observed pointing to energy transfer mechanisms between host and dopants. The electronic structure of Tb3+ defects inside the PbWO4 host are empirically deduced from optical and luminescence spectroscopy, both in steady-state as well as in time-resolved mode, as a function of temperature and doping concentration to asses the influence of key parameters in the energy transfer processes. The luminescence originating from Tb3+ ions shows a strong dependency on both the excitation wavelength and the temperature. For instance, an intensity increase in the 75–125K range upon excitation via the WO42− centres is found, which is absent for direct excitation. The undoped sample is characterized by a temperature-dependent energy transfer from WO42− to WO3 defect centres with an thermal energy barrier of 0.26eV. The divergent thermal quenching profiles of the host emission for pure PbWO4 versus doped materials reveal both a direct energy transfer and a temperature dependent energy transfer process from the host towards the Tb3+ ions. The emission efficiency of the 5DJ levels is investigated as well and a thermal quenching energy of 0.51eV (J=3) and 0.86eV (J=4) was found.

Unusual Concentration Induced Antithermal Quenching of the Bi(2+) Emission from Sr2P2O7:Bi(2.).

The resistance of a luminescent material to thermal quenching is essential for the application in high power LEDs. Usually, thermal luminescence quenching becomes more and more serious as the activator concentration increases. Conversely, we found here that a red phosphor Sr2P2O7:Bi(2+) is one of the exceptions to this as we studied the luminescence properties at low (10-300 K) and high (300-500 K) temperatures. As Bi(2+) ions are incorporated into Sr2P2O7, they exhibit the emissions at ∼660 and ∼698 nm at room temperature and are encoded, hereafter, as Bi(1) and Bi(2) due to the substitutions for two different crystallographic sites Sr(1) and Sr(2), respectively, in the compound. However, they will not substitute for these sites equally. At lower dopant concentration, they will occupy preferentially Sr(2) sites partially due to size match. As the concentration increases, more Bi(2+) ions start to occupy the Sr(1) sites. This can be verified by the distinct changes of emission intensity ratio of Bi(2) to Bi(1). As environment temperature increases, the thermal quenching happens, but it can be suppressed by the Bi(2+) concentration increase. This becomes even more pronounced in Bi(2+) heavily doped sample as we decompose the broad emission band into separated Bi(1) and Bi(2) Gaussian peaks. For the sample, the Bi(1) emission at ∼660 nm even shows antithermal-quenching particularly at higher temperatures. This phenomenon is accompanied by the blue shift of the overall emission band and almost no changes of lifetimes. A mechanism is proposed due to volume expansion of the unit cell, the increase of Bi(1) content, and temperature dependent energy transfer between Bi(2) and Bi(1). This work helps us better understand the complex luminescent behavior of Bi(2+) doped materials, and it will be helpful to design in the future the heavily doped phosphor for WLEDs with even better resistance to thermal quenching.