Papers by Keyword: Energy Transfer

Abstract: Optimizing the rare earth doping in inorganic binary glasses for tuneable structural and optical properties is ever-demanding for lasing glass. A series of Er³⁺ and Nd³⁺ doped lithium niobate tellurite glasses with compositions of (70-x-y)TeO₂–15Li₂CO₃–15Nb₂O₅–(x)Er₂O₃–(y)Nd₂O_3, where x = 0.0, 1.0 mol % and 0 ≤ y ≤ 1.0 mol% are synthesized using melt-quench technique. Influence of Nd³⁺ ion concentrations on physical and optical behaviour is examined. X–Ray diffraction pattern confirm the amorphous nature of glasses. The strong dependence of spectral properties on rare-earth dopant indicates the alteration in structures and bonding of glass network. The structural properties of the glass represented by the FTIR spectrum indicate that as Nd₂O₃ content increases, the sharp infrared absorption peaks are shifted from 474.7 cm^-1 to 499.4 cm^-1. These peaks are due to Nb-O, Te-O-Te and O-Te-O bond linkage bending vibrations. For TeO₄ trigonal bipyramid, the peak occurred at 676.5 cm^-1 whereas for TeO₃ trigonal pyramid, two infrared band peaks are found at 787.5 cm^-1 and 887.6cm^-1, respectively. The absorption peaks around 1382.7 cm^-1 is due to the Te – O – Nb stretching vibration while peaks at 1635.5cm^-1 and 3411.7 cm^-1 are due to the stretching vibrations of the hydroxyl group participating in the strong metal bonding as well as in the hydrogen bonding, respectively.

Abstract: Optimizing of the spectroscopic features of rare earth (RE) doped inorganic glasses via tuneable growth of metallic nanoparticles (NPs) is demanding in plasmonic based nanophotonics. We report the gold (Au) NPs assisted sizeable enhancements in Er³⁺ luminescence in zinc-sodium tellurite glass. Glasses of the form 70TeO₂-20ZnO-10Na₂O-(x)Er₂O₃-(y)Au (x = 0.0 and 1.0 mol%; y = 0.0-0.6 mol% in excess) are synthesized via melt-quenching method and thoroughly characterized. Au concentration dependent variations in the physical and spectroscopic properties of glasses are determined. XRD data confirms the amorphous nature of all samples. UV-Vis-NIR spectra reveal seven absorption bands corresponding to the transitions from ground state (⁴I_15/2) to ⁴I_13/2, ⁴I_11/2, ⁴I_9/2, ⁴F_9/2, ²H_11/2, ⁴F_7/2 and ⁴F_5/2 excited states of Er³⁺. TEM micrograph manifests the existence of non-spherical Au NPs with average size of 8.6 nm. Prominent surface plasmon band of Au NPs is evidenced around 629 nm. Furthermore, Au NPs display a SPR mediated strong absorption in the visible region. Room temperature visible down-conversion emission (under 425 nm excitation) reveal three significant peaks centred at 532 (moderate green represent ²H_11/2 → ⁴I_15/2 transition), 550 (weak green represent ⁴S_3/2 → ⁴I_15/2 transition) and 588 nm (strong green represent ⁴S_3/2 → ⁴I_15/2 transition). Glass containing 0.4 mol% of Au exhibiting the highest luminescence intensity is ascribed to the NPs local field enhancement and energy transfer between RE ions and NPs. Variations in the physical properties of glass are explained in terms of the alteration in structures and ligand interactions with Au NPs present in the glass network. The intense field amplification discerned in the vicinity of Au NPs is attributed to the charge accumulation at the surface of the NPs. Surface plasmon resonance (SPR) of Au NPs and energy transfer (ET) from NPs to Er³⁺ ions are primarily attributed for the observed spectral modification. It is established that our glass composition displaying such significant enhancement may be beneficial for the development of up-converted solid state lasers and other plasmonic devices.

Abstract: A series of red-emitting phosphors, Eu³⁺-doped and Eu³⁺ with Sm³⁺ co-doped Li₂CaSiO₄, were prepared by the combustion method. The phase composition was investigated by XRD, and photoluminescent properties were characterized by fluorescent spectrophotometer. The results show that the diffraction peaks of samples all match well with that of Li₂CaSiO₄ [JCPDS NO. 27-0290]. The excitation spectra consists of the broadband and the sharp lines, which are assigned to the charge transfer band (CTB) of Eu³⁺→O^2– and the typical intra-4f transitions of the Eu³⁺ ions, respectively. The emission spectrum covers the characteristic f-f transitions of Eu³⁺, namely, ⁵D₀→⁷F₁ (596 nm), ⁵D₀→⁷F₂ (620 nm), ⁵D₀→⁷F₃ (657 nm) and ⁵D₀→⁷F₄ (705 nm). The concentration quenching occurs when Eu³⁺ mol fraction equals to 9%. When Eu³⁺and Sm³⁺ were co-doped, the luminous intensity of the emission spectrum was superior to the Eu³⁺ mono-doped, which explains the Sm³⁺ has a sensitization effect for Eu³⁺.

Abstract: Na₂BaMgP₂O₈ phosphors were synthesized by a standard solid state reaction and their luminescent properties were investigated. The phase structure was analyzed by X-ray powder diffraction measurement. Under the excitation of 365nm, Na₂BaMgP₂O₈:Tb³⁺, Eu³⁺ phosphors show two color bands of green and red color due to ⁵D₄−⁷F₅ transition of Tb³⁺ ions and ⁵D₀−⁷F₂ transition of Eu³⁺ ions, respectively. The emission intensity of Tb³⁺ deceased with the increasing concentration of Eu³⁺, which verified that an effective energy transfer occurred from Tb³⁺ to Eu³⁺ in Na₂BaMgP₂O₈ host. The present study indicated that the phosphors have a high potential application in solid state lighting.

Abstract: One of the most surprising and significant advances in the study of the photosynthetic light-harvesting process is the discovery that the electronic energy transfer (ET) might involve long-lived electronic coherences, also at physiologically relevant conditions. This means that the transfer of energy among different chromophores does not follow the expected classical incoherent hopping mechanism, but that quantum-mechanical laws can steer the migration of energy. The implications of such quantum transport regime, although currently under debate, might have a tremendous impact in our way to think about natural and artificial light-harvesting and suggest new directions for the development of artificial devices for the efficient capture and re-use of solar energy. Central to these discoveries has been the development of new ultrafast spectroscopic techniques, in particular two-dimensional electronic spectroscopy, which is now the primary tool to obtain clear and definitive experimental proof of such effects.

Abstract: In a context of embedded structures, the next challenge is to develop an efficient, energetically autonomous vibration control technique. Synchronized Switch Damping techniques (SSD) have demonstrated interesting properties in vibration control with a low power consumption. The damping attenuation can be improved thanks to energy transfer between a voltage source and the SSD circuit. Harvesting energy on a second structure can provide this voltage source but drastically complex the overall system. We propose here a new technique to enhance the classic SSD circuit due to energy harvesting. Our original approach consists in transferring energy between modes of a same structure: energy is harvested on non-controlled mode to increase the attenuation of a targeted mode. In this paper, we present theoretical analysis and numerical simulations of our energy-transfer architecture applied to an academic case, a free-clamped beam. Our electrical architecture called Synchronized Switching Damping and Harvesting (SSDH) is composed of a harvesting circuit (Synchronized Switch Harvesting on Inductor SSHI), a dc-dc converter (Buck-Boost topology) and a vibration modal control circuit (similar to a Synchronized Switch on Voltage SSDV). In a multi-sine excitation, an increase of the attenuation damping of 3.8dB with our new technique compared to classic SSDI is achieved.

Abstract: In this study, fluorescence spectrum and UV-vis absorption spectrum were employed to explore the interactions between magnetic iron oxide nanoparticles modified by citric acid (CA-MION) and CdTe quantum dots modified by thioglycolic acid (TGA-CdTe QDs). Significantly, the mechanism was demonstrated as a dynamic quenching process based on energy transfer. Taken together, these results showed the decreased fluorescence intensity of CdTe QDs implied satisfactory linear relationship with various concentrations of CA-MION ranged from 0.15×10^-3 mol·L^-1 to 4.5×10^-3 mol·L^-1. Overall, this study has provided the potential for preparing multimagnetic-fluorescent nanocomposites and further developing quantitative detections of multi-analytes.

Abstract: Full face rock tunnel boring machine in construction process, disc cutter put pressure on rock breaking, actually belongs to the process of energy transfer, from the point of view of energy analysis the energy transfer rules in the process of disc cutter rock breaking, based on CSM force prediction model, analysis disc cutter energy input and rock mass energy output efficiency ratio, for excavation with minimum energy efficiency. Taking S-536 Hong Kong water tunnel TBM as an example, When the penetration is 10mm, based on the energy efficiency ratio the optimal disc cutter spacing should be less than 70mm, than the actual average disc cutter spacing is small 2mm, rock mass as a reference the disc cutter rock breaking efficiency mechanism provides certain reference value for the cutter layout.

Abstract: A series of Na₃YSi₂O₇: Eu³⁺, Sm³⁺ samples have been synthesized via solid-state reaction technique. The phase structure and luminescence properties are characterized using powder X-ray diffraction, photoluminescence excitation and emission spectra. Effective energy transfer occurs from Sm³⁺ to Eu³⁺ and Sm³⁺/Eu³⁺-codoped Na₃YSi₂O₇ shows more intense red light compared to that of Eu³⁺-doped sample under UV light excitation.

Abstract: CdSe semiconductor nano crystals (NCs) and Polyaniline (PAni) are mixed uniformly to prepare CdSe NCs/PAni complex. PAni can quench the fluorescent signal of CdSe NCs. The fluorescent intensity of CdSe NCs/PAni complex is related to the size of CdSe NCs and concentration of PAni. Ultraviolet visual (UV-Vis) absorption spectra and fluorescence spectra are employed to analysis the quenching phenomenon. The mechanism of fluorescence quench is dependent on two factors: on one hand, the FÖrster resonance energy transfer conducts from CdSe to PAni; on the other hand, PAni can intercept the electron charge of CdSe and lead to the interruption of radiative recombination.