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Novel A2-D-A1-D-A2 type NIR absorbing symmetrical squaraines based on 2, 3, 3, 8-tetramethyl-3H-pyrrolo [3, 2-h] quinoline: Synthesis, photophysical, electrochemical, thermal properties and photostability study
摘要： Two novel acceptor–donor-acceptor-donor-acceptor type pi-conjugated symmetrical squaraine dyes, denoted by PQSQ 1 and PQSQ 2 based on 2, 3, 3, 8-tetramethyl -3H-pyrrolo [3,2-h] quinoline were successfully synthesized for the first time to arrive absorption and emission at NIR region. These dyes comprise indolenines as electron donor units, squaryl ring as a central electron acceptor and pyridines as terminal electron acceptor units. The relationship between molecular structures and photophysical properties of these dyes was studied in comparison with their parent compounds (ISQ and N-Et ISQ). These novel squaraine dyes displayed an intense absorption within the range 671 to 692 nm in polar to non- polar solvents respectively with good molar extinction coefficients (? 105 Lmol-1cm-1). Compared to their parent squaraines, both dyes showed red-shifted absorption (33 - 44 nm) as well as emission (38 - 59 nm) due to the electron-accepting ability of the ancillary pyridine acceptors and extended pi-conjugation. These dyes exhibited negative solvatochromism and Reichardt's ET (30) scale was applied to propose a quantitative relationship of the relative stability of ground and excited-state of these squaraines with solvent polarity. The electrochemical and computational properties of these symmetrical squaraines were investigated with the help of cyclic voltammetry and density functional theory (DFT). Moreover, PQSQ 1-2 exhibited high thermal and photo-stability. These A2-D-A1-D-A2 type dyes showed improved photostabilities compared to their parent D-A-D type dyes.
关键词： 2, 3, 3, 8-tetramethyl -3H-pyrrolo [3, 2-h] quinoline,NIR absorbing dyes,acceptor-donor-acceptor-donor-acceptor,squaraines,DFT computations,red shift
更新于2025-09-23 15:21:21
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Red shift properties, crystal field theory and nephelauxetic effect on Mn4+-doped SrMgAl10-yGayO17 red phosphor for plant growth LED light
摘要： The discovery of novel Mn4+-doped oxide red phosphor with suitable spectrum for plant growth is a hot issue in the recent years due to the characteristic red photoluminescence of 2Eg → 4A2 transition in Mn4+ ions. Generally, the emission position of Mn4+ is hard to tune because of specific crystal field in most phosphors. In this work, tunable luminescence property with obvious red shift in the spectra is observed in the Mn4+-doped SrMgAl10-yGayO17 red phosphor via simple substitution of Ga3+ for Al3+, and crystal field theory and nephelauxetic effect are employed to explain this phenomenon. Meanwhile, the Ga3+ dopant changes the shape of the spectra because Ga3+ dopant guides the replacement site of Mn4+ and changes the luminescence center. Improved emission intensity is obtained because appropriate Ga3+ doping leads to larger band gap and reduces non-radiative transitions. Phosphor-converted LED (pc-LED) devices fabricated with blue chip (470 nm) and the as-obtained SrMgAl10-yGayO17:1.0%Mn4+ phosphors emit bright blue and red light, which fit the absorption regions of plant pigments well, thus SrMgAl10-yGayO17:Mn4+ phosphor can be a candidate for plant growth LED light.
关键词： crystal field theory,SrMgAl10-yGayO17:Mn4+,plant growth LED light,red shift,nephelauxetic effect
更新于2025-09-23 15:19:57
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A novel 1,8-naphthalimide as highly selective naked-eye and ratiometric fluorescent sensor for detection of Hg2+ ions
摘要： A novel colorimetric and ratiometric fluorescent chemosensor, 2-(2-mercaptophenyl)-1H-benzo[de]isoquinoline-1,3-(2H)-dione (L3) is reported for Hg2+ ions. The selective binding of Hg2+ to L3 afforded new absorbance and fluorescence peaks at 438 nm and 480 nm, in addition to the existing bands of L3 at 332 nm and 376 nm. It also showed apparent colour change from colourless to yellowish green and weak fluorescent to bright yellowish green strong fluorescent due to selective binding of Hg2+ ion. The sensor forms a 1:1 stoichiometry with high binding constants (3.89 × 10^4 mol^-1 L) and limit of detection 1.74 × 10^-8 M with high selectivity and sensitivity towards Hg2+ in the presence of other interfering metal ions. More importantly, it has good practicability in environmental water sample. The outcome of photo-physical experiment has also been in good accordance with the time-resolved fluorescence life decays and the density functional theory (DFT) estimations. Moreover, the L3-Hg2+ solution displayed high colorimetric and fluorimetric reversibility via the addition of KI. This reversibility in fluorescence showed potential applicability of chemosensor L3 as 'on–off–on' naked eye sensor.
关键词： Molecular logic gate,Red-shift,DFT,Off–on–off Hg2+ chemosensor,Naked eye detection,Ratiometric fluorescence
更新于2025-09-19 17:15:36
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Stress Relaxation in Porous GaN Prepared by UV Assisted Electrochemical Etching
摘要： This study describes the stress relaxation in porous GaN grown on Al2O3 substrates. The results indicate that the stress relaxation has taken place in the samples which increases by increasing the etching current. As compared to the as-grown GaN films, porous GaN exhibits substantial photoluminescence (PL) intensity enhancement with red-shifted band-edge peaks associated with the relaxation of the compressive stress. The red shifted phonon energy peak (E2) in the Raman spectra of the porous GaN films confirms further such a stress relaxation. Scanning electron microscopy (SEM) demonstrates that, the current density has significant effect on the size and shape of the pores.
关键词： Stress relaxation,Porous GaN,Raman spectroscopy,Red shift
更新于2025-09-19 17:15:36
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Red-shift effect in multi-color LEDs based visible light communication
摘要： Visible light communication (VLC) is a short range wireless optical communication system that provides lighting and data transmission, simultaneously. Besides lighting, in order to obtain high data rates, color-shift keying (CSK) which modulates the intensity of light using multi-color light emitting diodes (LEDs) has been introduced in IEEE 802.15.7 VLC standard. In CSK-based VLC (VLC-CSK) systems, some parameters of LEDs such as junction temperature is affected by physical and operation conditions. Junction temperature variations change the power spectral density (PSD) of LEDs, which is known as red-shift effect. In this study, the red-shift effect is examined for the first-time in VLC-CSK systems. The obtained numerical results show that the red-shift effect may dramatically reduce the performance of optical communication system. To eliminate the negative effect of red-shift, an effective solution based on the power normalization is proposed at the receiver side.
关键词： Visible light communication (VLC),red-shift effect,color shift keying (CSK),light-emitting diode (LED)
更新于2025-09-19 17:13:59
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Soliton Self-Frequency Shift in Mode Locked Fiber Lasers
摘要： We propose and demonstrate the soliton evolution in a mode locked Er-doped fiber laser with intra-cavity soliton self-frequency shift by numerical simulation, and analyze effects of different parameters including of pump strength, length of dispersion shift fiber (DSF), and modulation depth of saturable absorber in detail for the first time. The results show that once the stable output pulse is formed, the frequency shift amount would increase with increasing the pump strength or decreasing the length of DSF and the modulation depth.
关键词： fiber lasers,red shift,Soliton self-frequency shift,mode locked pulse
更新于2025-09-16 10:30:52
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Silver doping induced luminescence enhancement and red shift of gold nanoclusters with aggregation-induced emission
摘要： Deep understanding on the luminescence property of aggregation-induced emission (AIE) featured metal nanoclusters (NCs) is highly desired. This paper reports an systematic study on enhancing the luminescence of AIE-featured Au NCs, which is achieved by Ag doping to engineer the size/structure and aggregation states of the Au(I)-thiolate motifs in the NC shell. Moreover, by prolonging reaction time, the luminescence of the as-synthesized AuAg NCs could be further tailored from orange to red, which is also due to the variation of the Au(I)-thiolate motifs of NCs. This study can facilitate the better understanding of this AIE-featured luminescent probe and the design of other synthetic routes for this rising family of functional materials.
关键词： bimetallic,aggregation-induced emission,luminescence enhancement,nanoclusters,red shift
更新于2025-09-10 09:29:36
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New Source of the Red Shift of Highly-Excited Hydrogenic Spectral Lines in Astrophysical and Laboratory Plasmas
摘要： High-n hydrogen spectral lines (SL), n=13–17, studied in astrophysical and laboratory observations at the electron density Ne ~ 1013 cm-3 by Bengtson and Chester in 1972 (ApJ, p. 178, 565) exhibited red shifts by orders of magnitude greater than the theoretical shifts known up to now. Specifically, Bengtson and Chester presented the shifts of these SL observed in the spectra from Sirius and in the spectra from a radiofrequency discharge plasma in the laboratory: both types of the observations yielded red shifts that exceeded the corresponding theoretical shifts by orders of magnitude. In the present paper we introduce an additional source of the shift of high-n hydrogenic SL. We show that for high-n hydrogen SL it makes the primary contribution to the total red shift. We demonstrate that for the conditions of the astrophysical and laboratory observations from paper by Bengtson and Chester, this additional red shift is by orders of magnitude greater than the theoretical shifts known up to now. Finally we show that the allowance for this additional red shift removes the existed huge discrepancy between the observed and theoretical shifts of those that of high-n hydrogen SL.
关键词： Measurements,Shifts of hydrogen spectral lines,Astrophysical plasmas,Laboratory plasmas,Red shift
更新于2025-09-04 15:30:14