Polarized Fluorescence Spectra Research Articles

Identification of Short- and Long-Wavelength Emitting Chlorophylls in Cyanobacterial Photosystem I by Plasmon-Enhanced Single-Particle Spectroscopy at Room Temperature.

A peculiarity of cyanobacterial Photosystem I (PSI) is the presence of so-called red chlorophylls absorbing at wavelengths longer than the reaction center P700. The origin and function of these chlorophylls have been debated in literature, but so far no consensus has been reached on either question. Here, we use plasmon-enhanced single-particle fluorescence spectroscopy to elucidate the origin of both short- and long-wavelength emitting species in monomeric PSI from Thermosynechococcus elongatus at room temperature. Polarized fluorescence spectra of single PSI complexes reveal a phase shift in the modulation of the short-wavelength (687 nm) and long-wavelength (717 nm) peaks. Numerical simulations show that this phase shift reflects a spatial angle of 15° between the transition dipole moments of the two forms. Quantum chemical calculations, together with reported X-ray structural and spectroscopic data, were used to assign the chlorophyll a monomer A3 as a candidate for the short-wavelength emitter and the B31-B32 chlorophyll dimer as a candidate for the long-wavelength emitter.

Wide wavelength tuning on 4F3/2→4I13/2 transitions from Nd:ScYSiO5 laser

The polarized fluorescence spectra of the Nd:ScYSiO5 (Nd:SYSO) crystal were explored to manifest the tunable single- and multi-wavelength oscillations on the 4F3/2→4I13/2 transitions. A maximum continue-wave output power of 1.26 W was finally obtained from linear cavity. A birefringent filter (BF) was inserted into the V-cavity to achieve wavelength-tuning centered at 1346 nm, 1358 nm, and 1394 nm with tunable range of 4 nm, 6 nm, and 9 nm, respectively. Additionally, simultaneous multi-wavelength oscillation was obtained with the output power in the order of several hundred milliwatt.

Effects of Gold Nanoparticles on Fluorescence Polarization and Emission Spectra of Rhodamine 6G Solution

Fluorescence polarization and emission spectra of Rhodamine 6G solution with gold nanoparticles have been studied. It is found that the emission intensities tend to be low when the gold nanoparticles are added into the solution partly due to the energy transfer from the Rhodamine 6G to gold nanoparticles. The fluorescence polarization increases as the concentration ratio of the gold and Rhodamine 6G is more than 124 and decreases as the ratio is about 1115. The enhancement and reduction of fluorescence polarization values are understood as the shortening of the fluorescence lifetime and a temperature effect from the heating of gold nanoparticles, respectively.

Growth and spectroscopic properties of Sm3+:KY(WO4)2 crystal

A Sm3+:KY(WO4)2 crystal was grown by the modified Czochralski technique. Polarized absorption and fluorescence spectra, as well as a fluorescence decay curve, were recorded at room temperature. Radiative properties such as emission probabilities, branching ratios and radiative lifetimes were investigated within the framework of the Judd-Ofelt theory as well as the theory of f-f transition intensities which takes into account the influence of the excited configurations. Emission cross section spectra were determined. 4G5/2 fluorescence decay was analyzed within the framework of the Inokuti-Hirayama model. The spectroscopic properties of Sm:KYW crystal were compared with those of other Sm3+-doped materials.

Crystal growth, polarized spectroscopy and Judd-Ofelt analysis of Pr:YAlO3

Pr3+-doped YAlO3 (YAP) single crystal was successfully grown by the Czochralski (Cz) method. Polarized absorption and polarized fluorescence spectra were measured at the room temperature. The spectroscopic parameters based on the polarized absorption spectra were calculated by Judd-Ofelt (J-O) theory for the first time. The fluorescence lifetime of 3P0 energy level was fitted to be 19.16μs with the quantum efficiency of 95.8%. Through the analyzing of the spectroscopic properties, Pr:YAP crystal was demonstrated to be a promising candidate for solid state laser operation.

Disordered Nd:CaYAlO4 crystal lasing at 1069, 1080 and 1363 nm

The π- and σ-polarization laser operation in an a-cut disordered Nd: CaYAlO4 crystal were investigated. Making full use of the difference in polarized fluorescence spectra, σ-polarization laser at 1080nm and π-polarization laser at 1069nm were selected to oscillated by using of a polarizing beam splitting cube. Output powers of 2.45 and 1.52W were obtained at the pump power of 9.8W by rotating the laser crystal, respectively. 0.67W output power at wavelength of 1363nm was also achieved based on 4F3/2-4I13/2 transition using the cavity mirror designed for 1.3µm laser operation.

The effect of annulation of benzene rings on the photophysics and electronic structure of tetraazachlorin molecules

The photophysics and electronic structure of tribenzotetraazachlorins (H2, Zn, and Mg), which are novel analogues of phtalocyanines, have been studied experimentally and theoretically. At 293 K, the electronic absorption, fluorescence, and fluorescence excitation spectra are recorded and the fluorescence quantum yield and lifetime, as well as the quantum yield of singlet oxygen generation, are measured; at 77 K, the fluorescence, fluorescence excitation, and fluorescence polarization spectra are recorded and the fluorescence lifetime values are measured. The dependences of the absorption spectra and photophysical parameters on the structure variation are analyzed in detail. Quantum-chemical calculations of the electronic structure and absorption spectra of tribenzotetraazachlorins (H2, Mg) are performed using the INDO/Sm method (modified INDO/S method) based on molecular-geometry optimization by the DFT PBE/TZVP method. The results of quantum-chemical calculations of the electronic absorption spectra are in very good agreement with the experimental data for the transitions to two lower electronic states.

Spectroscopic properties of Sm3+-doped NaGd(MoO4)2 crystal for visible laser application

A NaGd(MoO4)2 crystal doped with 2at.% Sm3+ was grown by the Czochralski method. Polarized absorption and fluorescence spectra of the crystal were measured at room temperature. Spectroscopic parameters, including absorption and emission cross sections, Judd-Ofelt intensity parameters, radiative transition rates, fluorescence branching ratios, and fluorescence lifetime of the 4G5/2 multiplet, were obtained and compared with other Sm3+-doped crystals. The main fluorescence band around 646nm is related to the 4G5/2→6H9/2 transition, which has a branching ratio of 45.4% and peak emission cross sections of 1.73×10–21 and 3.13×10–21cm2 for π and σ polarizations, respectively. The results indicate that the Sm3+:NaGd(MoO4)2 crystal may be a potential gain medium of red visible laser pumped directly by commercially available 405nm laser diode.

Crystal growth and spectroscopic properties of Cr3+-doped CaGdAlO4

A Cr3+:CaGdAlO4 single crystal with dimensions of ∅21×33mm3 was grown successfully by Czochralski method for the first time. Its spectral properties including polarized absorption spectra, polarized fluorescence spectra, excitation spectrum and fluorescence decay curves were investigated in detail. The absorption cross-sections at around 573nm corresponding to the 4A2→4T2 transition of Cr3+ ions are 4.75×10−20 and 2.56×10−20cm2 for σ- and π-polarizations, respectively. The excitation spectrum shows two broad and intense absorption bands at about 390nm and 570nm, which are associated with the 4A2→4T1 and 4A2→4T2 transitions of Cr3+ ions, respectively. The emission band with peak at around 744nm is ascribed to the 2E→4A2 transition of Cr3+ ions, with the emission cross-sections of 5.55×10−22 and 5.41×10−22cm2 for σ- and π-polarizations, respectively. The fluorescence lifetime is 4.35ms at room temperature. The Dq/B value is 2.72, which means that Cr3+ ions occupy the lattice sites with strong crystal field strength. The results show that Cr3+:CaGdAlO4 crystal can be regarded as a potential laser gain medium.

Blood fluorescence polarization characteristics of saturated fatty acid biological effects

The fluorescence spectra of normal and lard diet intake whole blood solution induced by a laser with an excitation wavelength of 407nm, and the polarization fluorescence spectra at angles of 0°, 35°, 55° and 90° were studied experimentally. The polarization state was tested by fluorescence intensity Stokes vector parameters. Through Mueller matrix calculations, we discuss the polarization degrees of whole blood solution during different time, the effects on fluorescence parameters of whole blood solution after lard diet intake. The results show that both the main fluorescence peaks of normal and lard diet intake whole blood solution locate at about 612nm. The polarization degree of the whole blood solution after lard diet intake fluctuates greatly and is evidently higher than that of normal one. It is analyzed that growing blood cells in size and increasing blood viscosity make the molecular rotation of lard diet intake hindered.

Selection of π- and σ-polarization laser emission in Nd:Lu0.5Y0.5VO4 mixed crystal

Polarized fluorescence spectra and laser emission of π- and σ-polarization were investigated with a Nd: Lu0.5Y0.5VO4 mixed crystal. A polarizing beam splitting cube was proposed for active selection of oscillating polarization. At a pump power of 12.4W, 5.72W single wavelength laser at 1065.1nm and 3.55W dual-wavelength laser at 1064.9 and 1067.3nm were obtained for π- and σ-polarization, respectively. The wavelength at 1341nm for both polarization output were also studied. The broader fluorescence spectra with σ-polarization will be excellent in ultra-short pulses production.

Polarized spectroscopic properties of Er3+:Gd2SiO5 crystal and evaluation of Er3+:Yb3+:Gd2SiO5 crystal as a 1.55 μm laser medium

An Er3+-doped Gd2SiO5 single crystal with high optical quality has been grown by the Czochralski method. Polarized absorption and fluorescence spectra and fluorescence lifetime of the crystal were measured at room temperature. Intensity parameters, spontaneous emission probabilities, fluorescence branching ratios, and radiative lifetimes were estimated on the basis of the Judd–Ofelt theory. Besides, potentiality of 1.55μm laser emission in an Er3+–Yb3+ co-doped Gd2SiO5 crystal was evaluated.

Polarized spectroscopic properties and continuous-wave laser operation of Yb:Gd2SiO5 crystal

Yb3+:Gd2SiO5 single crystal with Yb3+ concentration of 6.33 at.% was grown by the Czochralski method. Polarized absorption and fluorescence spectra were measured at room temperature. Intrinsic fluorescence lifetime of the 2F5/2 multiplet was measured to be 0.87 ms when the powder of Yb3+:Gd2SiO5 crystal with low Yb3+ concentration of 0.5 at.% immersed in refractive index-matching fluid was adopted to weaken the influence of radiation trapping and concentration dependent fluorescence quenching. Furthermore, diode-pumped continuous-wave laser around 1090 nm with a slope efficiency of 52% and maximum output power of 1.2 W was demonstrated in the crystal.

Study on the Fluorescence Spectra Characteristics of Vinegar-Water Solutions

Fluorescence spectra and polarization spectra of vinegar-water solutions with different concentration of CH3COOH have been studied. The characteristics and mechanism of fluorescence spectra are discussed, and polarization degree is calculated. Vinegar-water solutions are excited by ultraviolet (UV) light at 380 nm. The characteristic fluorescence peaks of the solution were identified at 445 nm and 470 nm. The type of emission fluorescence isπ⁎→n. With the increasing concentration of CH3COOH/pH value, the peak intensity is enhanced first, and then fluorescence quenching occurs. The polarization degree confirms the molecular orientation of different sample solutions. This research provides theoretical and experimental basis for the physical/chemical properties and quality of vinegar detection by florescence spectroscopy.

Spectral and Luminescent Characteristics of a Hexaphenyltetraazachlorin Zinc Complex

In continuation of previous studies on the photophysics of phenyl-substituted tetraazachlorins, we determined the spectral and luminescent characteristics of a tetramethylhexaphenyltetraazachlorin zinc complex at 293 and 77 K. Absorption, fluorescence, and fluorescence excitation spectra; the fluorescence quantum yield and lifetime; and the quantum yield for singlet oxygen generation were measured at room temperature. Fluorescence, fluorescence excitation, and fluorescence polarization spectra were measured at liquid nitrogen temperature. Fluorescence spectra indicated that the zinc complex rearranged in the excited electronic state S1 at both temperatures. A high quantum yield for singlet oxygen generation (0.91) was obtained for a toluene solution. Zn-tetramethylhexaphenyl tetraazachlorin was proposed as a photosensitizer for photodynamic therapy because the long-wavelength band at 707 nm was located in the transparent region of biological tissues.

Polarized spectral properties of Sm3+:LiLuF4 crystal for visible laser application

A Sm3+-doped LiLuF4 single crystal was grown by the vertical Bridgman–Stockbarge technique. Polarized absorption spectra, polarized fluorescence spectra, and fluorescence lifetime of the Sm3+:LiLuF4 crystal were recorded at room temperature. Based on the Judd–Ofelt theory, spectral parameters of the Sm3+:LiLuF4 crystal were calculated. Emission cross sections for the 4G5/2→6HJ (J=5/2, 7/2, 9/2, and 11/2) transitions with special interest for visible laser application were obtained by the Füchtbauer–Ladenburg formula. The results indicate that the Sm3+:LiLuF4 crystal may be a potential laser gain medium operating in visible region pumped by diode lasers around 401nm.

Growth, thermal properties and laser operation of a new disordered crystal: Nd-doped Sr3La2(BO3)4

A novel disordered laser crystal Nd:Sr3La2(BO3)4 is characterized including its crystal growth, structure, thermal properties, inhomogeneously broadened spectra, and laser performance, which result that this crystal should be a promising gain material for the high-power ultrashort pulsed neodymium laser. The complete set of anisotropic thermal properties were systematically studied for the first time. It has been found that all the thermal conductivities along the three crystallographic directions increase with temperature, indicating a glass-like behavior. Polarized absorption and fluorescence spectra of Nd:Sr3La2(BO3)4 crystal were measured at 298.15K and 77.2K, respectively. The results show that both the absorption and the emission spectra of Nd3+ have been inhomogeneously broadened, and thus it is very promising to be used in laser systems to produce femtosecond pulses. CW laser operations at 1.06μm along the b-cut and c-cut directions have been demonstrated for the first time. A maximum power of 533mW with an optical conversion efficiency of 5.5% and slope efficiency of 6.4% was achieved in the c-cut sample.

Crystal growth, nonlinear frequency-doubling and spectral characteristic of Nd:Ca9La(VO4)7 crystal

The pure Ca9La(VO4)7 and the Nd:Ca9La(VO4)7 crystals with various Nd3+-doped concentrations were grown by Czochraski method. The effective segregation coefficient of Nd3+ ion in Ca9La(VO4)7 crystal was measured as 1.07, which is favorable to the even distribution of Nd3+ ions. The frequency-doubling experiment and the crystal structure analyses show that the presence of La3+ ion in crystal can improve the SHG effect of Ca9La(VO4)7 crystal. The intensity of SHG effect, measured by the Kurtz powder method, is found to be about 4 times as large as that of KH2PO4 (KDP) crystal. The polarized absorption spectra and the polarized fluorescence spectra are analyzed based on Judd–Ofelt theory, which show that the Nd:Ca9La(VO4)7 crystal is hopeful to generate laser light at the wavelengths of about 921, 1069 and 1349nm. The luminescence decay kinetics are analyzed based on the migration model, and the results indicate that Nd3+ ion in Ca9La(VO4)7 crystal has a high quantum efficiency, about 98.2% in 3.2at.% Nd:Ca9La(VO4)7 crystal, and a weak concentration quenching effect. Therefore, Nd:Ca9La(VO4)7 crystal may be a high efficiency laser material and a candidate of self-frequency-doubling (SFD) laser crystal.

Comprehensive studies on the interaction of copper nanoparticles with bovine serum albumin using various spectroscopies

Copper nanoparticles (NPs) of average size of ∼7.5nm were synthesized by chemical reduction method. Fluorescence spectroscopy in synchronous and polarization modes were used to examine the nature of interaction between Cu NPs and bovine serum albumin (BSA) at different temperatures. Fluorescence quenching results suggest that Cu NPs interact with BSA molecule through static mechanism, as inferred from the quenching of BSA fluorophore. The calculated thermodynamic parameters (ΔG°, ΔH°, and ΔS°) hint that the binding process occurs spontaneously by involving hydrophobic forces. Synchronous fluorescence spectra reveal that the interaction of Cu NPs with BSA mostly changes the microenvironment of tryptophan and not of tyrosine residues. The formation of BSA–Cu NPs ground state complex was also confirmed from the resonant light scattering and fluorescence polarization spectra. Circular dichroism and Raman spectra indicate that α-helicity of the BSA decreases due to the interaction with Cu NPs. It was also found that Cu NPs are located in the close proximity of BSA molecule, which transfer energy efficiently from the excited state of BSA fluorophore to the Cu NPs.

Growth and spectral properties of Nd3+:Ba2LiNb5O15 crystal

Nd3+ doped Ba2LiNb5O15 single crystals with dimension Ø10×30mm3 were grown by the Czochralski technique. The refractive indexes were measured. The polarized absorption spectra, polarized fluorescence spectra and fluorescence decay curve were measured at 300K and the spectral parameters were calculated according to Judd–Ofelt theory. These results indicate that Nd3+:Ba2LiNb5O15 crystal can be regarded as a laser crystal.