Radiative Energy Transfer Processes Research Articles

Producing circularly polarized luminescence by radiative energy transfer from achiral metal-organic cage to chiral organic molecules

The development of circularly polarized luminescence (CPL) materials with high performance is significantly important. Herein, we develop a facial strategy for fabricating a CPL-active system by employing an achiral luminescent metal-organic cage (MOC) and chiral boron dipyrromethene (BODIPY) molecules. CPL is achieved by taking advantage of the radiative energy transfer process, in which BODIPY molecules act as energy acceptors and MOCs act as donors. The CPL performance (maximum luminescence dissymmetry factor up to ±1.5×10−3) can be tuned by adjusting the ratio between MOCs and BODIPY. White-light emission with the CPL feature is obtained by using a ternary system including MOC, chiral BODIPY, and Rhodamine B. The present work provides a facile and universal strategy to construct a CPL-active system by integrating achiral luminophores and chiral molecules.

Effect of radiative and nonradiative energy transfer processes of light-emitting diodes combined with quantum dots for visible light communication

Though light-emitting diodes (LEDs) combined with various color conversion techniques have been widely explored for VLC (visible light communication), E-O (electro-optical) frequency responses of devices with quantum dots (QDs) embedded within the nanoholes have rarely been addressed. Here we propose LEDs with embedded photonic crystal (PhC) nanohole patterns and green light QDs for studying small-signal E-O frequency bandwidths and large signal on–off keying E-O responses. We observe that the E-O modulation quality of PhC LEDs with QDs is better than a conventional LED with QDs when the overall blue mixed with green light output signal is considered. However, the optical response of only QD converted green light shows a contradictory result. The slower E-O conversion response is attributed to multi-path green light generation from both radiative and nonradiative energy transfer processes for QDs coated on the PhC LEDs.

Improved scintillation intensity of CsPbBr3 perovskite film via introducing BaLuF5: Gd/Tb nanoparticles

Metal halide perovskites nanoparticles (PNPs) show promising application in X-ray detection and imaging. However, they exhibit poor stability, especially, the emission peak might be evidently shifted with increasing the PNPs concentration. In this work, the composites of CsPbBr3 PNPs and BaLuF5: 15Gd/15Tb NPs are used to prepare scintillation film for the first time. When fixing the PNPs content in the film, its emission center is not changed after the addition of fluoride NPs. The uniform film containing both BaLuF5: 15Gd/15Tb to CsPbBr3 is prepared. The scintillation intensity of the CsPbBr3 PNPs is enhanced owing to the radiative energy transfer process from BaLuF5: 15Gd/15Tb to CsPbBr3. Our results provide a novel route to improve the scintillation intensity, which might promote the exploration of new scintillators with high performance.

Colourful organic afterglow materials with super-wide color gamut and scaled processability from cellulose

Multi-colour afterglow materials have attracted widespread attention recently, because they not only can eliminate the interference of scattered light and background fluorescence, but also store the richer information. In this work, the phosphorescence emission of cellulose-based nitrogen-doped carbon dots (CDs) was transferred to the rhodamine derivatives via an efficient radiative energy transfer process, because of the strong electrostatic attraction interactions between the positive charged CDs and the negative charged rhodamine derivatives. As a result, multi-color afterglow luminescence with tunable emission and wide color gamut was realized from blue-green to green, yellow, orange and red. With the contribution of the excellent processability of polymer materials, multi-color afterglow films, coatings, fibers and patterns were readily obtained, indicating a practical application in advanced anti-counterfeiting and multiple-mode information encryption. Such a facile, universal and efficient strategy to construct multi-colour afterglow materials inspires us to understand the luminescence process and design novel afterglow materials.

A Universal Strategy for Tunable Persistent Luminescent Materials via Radiative Energy Transfer

AbstractIn this work, a universal strategy for solid, solution, or gel state organic persistent luminescent materials via radiative energy transfer is proposed. The persistent luminescence (τ>0.7 s) could be remotely regulated between different colors by controlling the isomerization of the energy acceptor. The function relies on the simple radiative energy transfer (reabsorption) mechanism, rather than the complicated communication between the excited state of the molecules such as Förster resonance energy transfer or Dexter energy transfer. And the “apparent lifetime” for the energy acceptor is the same as the lifetime of the energy donor, which was different with a traditional radiative energy transfer process. The simple working principle endows this strategy with huge universality, flexibility, and operability. This work offers a simple, feasible, and universal way to construct various persistent luminescent materials in solid, solution, and gel states.

A Universal Strategy for Tunable Persistent Luminescent Materials via Radiative Energy Transfer.

In this work, a universal strategy for solid, solution, or gel state organic persistent luminescent materials via radiative energy transfer is proposed. The persistent luminescence (τ>0.7 s) could be remotely regulated between different colors by controlling the isomerization of the energy acceptor. The function relies on the simple radiative energy transfer (reabsorption) mechanism, rather than the complicated communication between the excited state of the molecules such as Förster resonance energy transfer or Dexter energy transfer. And the "apparent lifetime" for the energy acceptor is the same as the lifetime of the energy donor, which was different with a traditional radiative energy transfer process. The simple working principle endows this strategy with huge universality, flexibility, and operability. This work offers a simple, feasible, and universal way to construct various persistent luminescent materials in solid, solution, and gel states.

The Microscale Urban Surface Energy (MUSE) Model for Real Urban Application

Urban atmospheric environmental issues are commonly associated with the physical processes of urban surfaces. Much progress has been made on the building-resolving microscale atmospheric models, but a realistic representation of the physical processes of urban surfaces on those models is still lacking. This study presents a new microscale urban surface energy (MUSE) model for real urban meteorological and environmental applications that is capable of representing the urban radiative, convective, and conductive energy transfer processes along with their interactions, and that is directly compatible with the Cartesian grid microscale atmospheric models. The physical processes of shadow casting and radiative transfers were validated on an analytical accuracy level. The full capability of the model in simulating the three-dimensional surface heterogeneities in a real urban environment was tested for a hot summer day in August 2016 using the field measurements obtained from the Kongju National University campus, South Korea. The validation against the measurements showed that the model is capable of predicting surface temperatures and energy balance fluxes in a patch scale at the heterogeneous urban surfaces by virtue of the interactive representation of the urban physical processes. The excellent performance and flexible grid design emphasize the potential capabilities of the MUSE model for use in urban meteorological and environmental applications through the building-resolving microscale atmospheric models, such as computational fluid dynamics (CFD) and large-eddy simulations (LES).

A novel single-phase Na3.6Y1.8(PO4)3:Bi3+,Eu3+ phosphor for tunable and white light emission

A new type of Bi3+,Eu3+ single- and co-doped Na3.6Y1.8(PO4)3 phosphate phosphors were manufactured using conventional high-temperature solid-state reaction technique to explore their application for solid-state lighting. The crystal structure, luminescent properties, luminescent mechanism and quantum efficiency were thoroughly explored. Results show that there are two crystallization sites for Bi3+ and Eu3+ ions. Upon the excitation of 342 and 373 nm, Bi3+ single-doped phosphors exhibit green and blue emission, derived from the 3P1 to 1S0 transition of Bi3+ located in different occupancy sites. Thanks to radiative energy transfer process from Bi3+ to Eu3+, adjustable emission could be acquired by altering Eu3+ content in co-doped phosphors. Pure white-light emission with quantum efficiency value of 22.9% can be realized in Na3.6Y1.8(PO4)3:0.01Bi3+,0.1Eu3+ sample and the integrated intensity of white light emission at 417 K remains 85% of that at room temperature. Our results indicate that Na3.6Y1.8(PO4)3:Bi3+,Eu3+ phosphors have feasible application in high-power ultraviolet driven solid-state lighting.

Electric-Field-Regulated Energy Transfer in Chiral Liquid Crystals for Enhancing Upconverted Circularly Polarized Luminescence through Steering the Photonic Bandgap.

Circularly polarized luminescent materials with high dissymmetry factor (glum ) have been attracting increasing attention due to their distinctive photonic properties. In this work, by incorporating upconversion nanoparticles (UCNPs) and CsPbBr3 perovskite nanocrystals (PKNCs) into a chiral nematic liquid crystal (N*LC), enhanced upconverted circularly polarized luminescence (UC-CPL) based on a radiative energy transfer (RET) process from UCNPs to CsPbBr3 PKNCs is successfully implemented. By locating the emission peak of CsPbBr3 PKNCs at the center of the photonic bandgap of N*LC, the maximum glum value of UC-CPL can be amplified to an extremely large value of 1.1. Meanwhile, upconverted emission of UCNPs can be significantly enhanced due to the band edge enhancement effect of the N*LC, subsequently enhancing the emission of the CsPbBr3 PKNCs through the RET process. In addition, an applied electric field can switch the upconverted emission of the UCNPs, as well as the RET process, enabling an electric-field-controlled UC-CPL switch.

Time-resolved spectroscopy of radiative energy transfer between a conjugated oligomer and polymer in solution.

We report a short investigation of the energy transfer process between the conjugated oligomer 1,4-bis(9-ethyl-3-carbazo-vinylene)-9,9-dihexyl-fluorene (BECV-DHF) and the conjugated polymer poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylene-vinylene] - end capped with DMP (MDMO-PPV). The radiative energy transfer (RET) process shows a time delay, and the formation of the excimer causes a further delay. All these processes were studied using time-resolved spectroscopy (TRS), which has three-dimensional (3D) features with wavelength, intensity and time (picosecond) as the X, Y and Z-axis, respectively. We observed a definitive delay (1ns) in the fluorescence from MEDMO-PPV concerning the fluorescence of the oligomer, indicating the RET. The TRS of different relative concentrations and temperature effects on the energy transfer process was also studied. The quantum yield, critical distance, polarizability and change of MEDMO-PPV were calculated. The excimer of the MEDMO-PPV produces Amplified Spontaneous Emission (ASE) after a time delay of at least 0.5ns, which was also observed in this study.

Highly efficient and thermally stable Cr3+-activated silicate phosphors for broadband near-infrared LED applications

A novel broadband near-infrared (NIR) phosphor LiInSi2O6:Cr3+ (LIS:Cr3+) is successfully synthesized via solid-state reaction. Its crystal structure, photoluminescence properties as well as the application in NIR phosphor-converted LEDs (pc-LEDs) are explored. The LIS:Cr3+ phosphor has two absorptions bands centered at ~460 and 670 nm, respectively. Under 460 nm excitation, it shows the broadband NIR emission peaking at ~840 nm with a full width at half maximum (FWHM) of ~143 nm. The optimum Cr3+ concentration is found to be ~6 mol%, whereas the intensity decrease at further increased Cr3+ content is attributed to the radiative energy transfer process. The LIS:0.06Cr3+ phosphor has a quantum yield of ~75% and can retain ~77% of the initial intensity at 150 °C. Highly efficient, thermally stable and broad NIR emissions of LIS:Cr3+ phosphors are caused by the Cr3+ preferential occupancy in [InO6] octahedron with weak crystal field but relatively strong rigidity. The NIR pc-LED is fabricated by combining the LIS:Cr3+ phosphor with the blue LED chip, which has the NIR output power of ~51.6 mW and the photoelectric efficiency of ~17.8% at 100 mA drive current. The results suggest that LIS:Cr3+ phosphors have great potential for applications in broadband NIR pc-LEDs.

Effect of the interaction distance on 614 nm red emission from Eu3+ ions due to the energy transfer from ZnO-nc to Eu3+ ions

In this work, we study the effect of the average shortest interaction distance between zinc oxide nanocrystals (ZnO-nc) and Europium (Eu3+) ions and between two Eu3+ ions in the energy transfer process between ZnO-nc and Eu3+ ions embedded in a SiO2 matrix fabricated by a combination of sol-gel and the sputtering technique. A detailed model to calculate the two interaction distances based on the ratio of Zn, Si and Eu3+ ions in the samples and using the density and molecular mass of ZnO and SiO2 is presented. Based on these calculations together with the photoluminescence emission from the samples, it is clearly shown that the energy transfer from ZnO-nc to Eu3+ ions is higher in samples with a shorter distance between the ZnO-nc and Eu3+ ions. The maximum red emission at 614 nm due to the efficient energy transfer from ZnO-nc to Eu3+ was found in the sample with 5.11 nm distance between the ZnO-nc and Eu3+ ions. However, the red emission from the Eu3+ ions does not increase as the distance between the ZnO-nc and Eu3+ ions is reduced below 5.11 nm by increasing the Eu3+ concentration. This is due to the Eu3+ ion concentration quenching effect, where the distances between the Eu3+ ions become shorter than 0.57 nm, resulting in a migration of energy between the Eu3+ ions that is non-radiatively dissipated. It is also shown that the energy transfer from ZnO-nc to Eu3+ ions occur mostly due to the radiative energy transfer process when the interaction distance between the ZnO-nc and Eu3+ ions is 6.53 nm or greater.

Biomass evaluation by the use of Landsat satellite imagery and forestry data

Satellite imagery allows to estimate vegetation parameters related to large areas and to evaluate biogeochemical cycles and radiative energy transfer processes between soil/vegetation and atmosphere.Moreover, the spectral indices derived from remote sensed data can be used for biomass estimation.This paper focuses on the evaluation of above-ground biomass in the Leonessa Municipality, Latium Region (Italy) by the use of Landsat 7 ETM+ (2001) and Landsat 8-OLI (2015) data. To achieve this goal, Rural Development Programs (PSR) and Forest Management Plans(FMP) (2001-2010) have been analyzed to retrieve the main information related to the different types of wood resources. In particular, dendrometry and prospects of different cultivation classes provide the main data such as the extension (ha), the biomass production (m3/ha), the number of plants, the cuts plan of each Forest Management Unit (FMU). This dataset was organized within a Geographical Information System (GIS) as well as Landsat images.Landsat 7 imagery was classified with two spectral indices, Normalized Difference Vegetation Index (NDVI) and Tasseled Cup, in order to find a correlation between remote sensed data and biomass production in m3/ha. Once obtained the spectral model, the analysis was extended to Landsat 8 and the 2015 biomass map was produced and exported on the web. The results, obtained by the exclusively analysis of open source optical remote sensing data, demonstrate their suitability to update FMPs with lower cost if compared to canonical field methods. Additionally, the analysis allows to extend the investigation to un-analyzed areas by forestry studies, too.

Photoluminescence and energy transfer investigation from SiO2: Tb, Au inverse opals to rhodamine-B dyes

Energy transfer has attracted extensive attention due to its widespread applications in medical diagnostics, DNA analysis and lighting devices. There are few reports on the energy transfer from rare earth ions to dyes. In the present work, the SiO2:Tb inverse opals with and without Au nanoparticles were prepared, and the organic rhodamine-B (RhB) dyes were filled into the voids of SiO2:Tb inverse opals. Non-radiative and radiative energy transfer processes from the SiO2:Tb inverse opals to the RhB were observed. The influence of Au nanoparticles and photonic band gap on the energy transfer from SiO2:Tb inverse opals to the RhB was investigated. The Au nanoparticles enhanced energy transfer was observed due to the surface plasmon resonance effects of the Au nanoparticles. When the emission peaks from the SiO2:Tb inverse opal is overlapped with the photonic band gap, the emission suppression of the SiO2:Tb inverse opal as well the emission enhancement of the RhB dyes were obtained, which is attributed to improved energy transfer caused by the photonic band gap. The steady state rate equations were used to explain enhancement of energy transfer caused by the photonic band gap.

Quantum emitter coupled to plasmonic nanotriangle: Spatially dependent emission and thermal mapping

Herein we report on our studies of radiative and non-radiative interaction between an individual quantum emitter and an anisotropic plasmonic nanostructure: a gold nanotriangle. Our theoretical and three-dimensional electromagnetic simulation studies highlight an interesting connection between: dipole-orientation of the quantum emitter, anisotropy of the plasmonic nanostructure and, radiative and non-radiative energy transfer processes between the emitter and the plasmonic geometry. For the out of plane orientation of quantum emitter, the total decay rate and non-radiative decay rate was found to be maximum, showing radiation extraction efficiency of 0.678. Also the radiative decay rate was greater for the same orientation, and showed a pronounced spatial dependence with respect to the nanotriangle. Our study has direct implication on two aspects: designing nanoparticle optical antennas to control emission from individual atoms and molecules and geometrical control of quenching of emission into plasmonic decay channels.

Aluminum plasmonic photocatalysis.

The effectiveness of photocatalytic processes is dictated largely by plasmonic materials with the capability to enhance light absorption as well as the energy conversion efficiency. Herein, we demonstrate how to improve the plasmonic photocatalytic properties of TiO2/Al nano-void arrays by overlapping the localized surface plasmon resonance (LSPR) modes with the TiO2 band gap. The plasmonic TiO2/Al arrays exhibit superior photocatalytic activity boasting an enhancement of 7.2 folds. The underlying mechanisms concerning the radiative energy transfer and interface energy transfer processes are discussed. Both processes occur at the TiO2/Al interface and their contributions to photocatalysis are evaluated. The results are important to the optimization of aluminum plasmonic materials in photocatalytic applications.

Optical characterization of Er3+-doped zinc fluorophosphate glasses for optical temperature sensors

Trivalent erbium doped zinc fluorophosphate glasses have been synthesized and their luminescence properties in the green visible range have been investigated as a function of temperature. The Judd–Ofelt theory has been used to predict the transition probabilities, branching ratios and lifetimes for the various excited states of Er3+ ions in 0.5mol% of Er2O3-doped glass. The effect of Er3+ concentration on temperature dependent luminescence has been studied for the wide temperature range from room temperature up to 773K. The fluorescence intensity ratio of the green emissions associated to the two transitions from the thermally coupled 2H11/2 and 4S3/2 levels to the 4I15/2 level of Er3+ ion has been studied as a function of temperature, and in turn used to determine the thermal sensitivity and relative thermal sensitivity of the glasses. In the present study, the maximum value for the thermal sensitivity of 79×10−4K−1 at 630K has been obtained for the lowest (0.01mol%) concentration of Er2O3-doped glass, one of the highest sensitivity found in the literature and quite close to the theoretical sensitivity calculated from the Judd–Ofelt theory. The results reveal that the zinc fluorophosphate glass having relatively low concentration of Er3+ ions can be useful as an optical temperature sensor due to their high sensitivity and the absence of radiative energy transfer processes.

Radiative resonant energy transfer process in projectile-like ion formed in beam-foil interaction

The formation of projectile-like M2555n ion during bombardment of a thin carbon foil by V12+2351 ion beam of energies above the Coulomb barrier is inferred through the observation of unresolved 1s2pP2o3→1s2S01 and 1s2pP0o3→1s2S01 transitions of He-like Mn at 6.14keV. From the decay of intensity of this line the measured radiative lifetime of the upper state is found to be 78.7±11.6ps which is close to the theoretical lifetime of the 1s2pP0o3 state (86.18ps), but substantially lower than that of 1s2pP2o3 state (147.1ps). This suggests that the 1s2pP0o3 state is populated more than the 1s2pP2o3 state when He-like Mn exits the carbon foil. This behavior is explained on the basis of radiative resonant energy transfer process in beam-foil excitation as reported recently (Nandi T, et al. J Quant Spectrosc Radiat Transfer 2012;113:783–8).

Effects of Er3+ concentration on thermal sensitivity in optical temperature fluorotellurite glass sensors

Abstract The effects of Er 3+ concentration on temperature-dependent luminescence in fluorotellurite glass were studied in the 100–573 K range for its application as an optical temperature sensor. The temperature-induced changes in the Er 3+ green emissions associated to the transitions from the 2 H 11/2 and 4 S 3/2 thermalized levels to the 4 I 15/2 ground state were calibrated by doping the fluorotellurite glasses with three concentrations (0.01, 0.1 and 2.5 mol% of Er 3+ ions) and using commercial cw 488 nm laser excitation. The intensities, quantum efficiencies, line profiles and fluorescence intensity ratio of these thermalized green emitting levels are highly dependent on the optically active Er 3+ concentration and the position of the glass excited by the laser beam due to the existence of radiative and non-radiative energy transfer processes between Er 3+ ions. The maximum value for thermal sensitivity were obtained for the fluorotellurite glass doped with the lowest concentration of Er 3+ ions, 79 × 10 −4 K −1 at 541 K, one of the highest values found in the literature, and quite close to the theoretical thermal sensitivity calculated using the Judd–Ofelt theory. This study concludes that the calibration of optical temperature sensors based on Er 3+ ions is strongly affected by radiative energy transfer processes, therefore a relatively low concentration of Er 3+ ions should be used to avoid them.

Silica cross-linked nanoparticles encapsulating fluorescent conjugated dyes for energy transfer-based white light emission and porphyrin sensing

This work demonstrated that water-soluble fluorescent hybrid materials can be successfully synthesized by use of silica cross-linked micellar nanoparticles (SCMNPs) as scaffolds to encapsulate fluorescent conjugated dyes for pH sensing, porphyrin sensing and tunable colour emission. Three dyes were separately encapsulated inside SCMNPs (short to dye-SCMNPs). Each of the dye-SCMNPs indicated longer lifetime in water than that of free dye dissolved in organic solvent. The 7-(hexadecyloxy) coumarin-3-ethylformate (HCE) encapsulated inside SCMNPs (HCE-SCMNPs) exhibited fluorescence quenching by pH change in aqueous media. Furthermore, it was confirmed that the radiative and nonradiative energy transfer processes both occurred between HCE-SCMNPs and tetraphenyl-porphyrin (TPP), which were used to synthesize the water-soluble TPP sensor. Significantly, HCE-SCMNPs doped with 5,12-dicotyl-quinacridone (8CQA) and TPP showed water-soluble white light emission (CIE (0.29, 0.34)) upon singlet excitation of 376 nm due to colour adjustment of 8CQA and energy transfer from HCE (donor) to TPP (acceptor).