Two-photon Upconversion Fluorescence Research Articles

Synthesis and two-photon up-conversion sensing property of pyridinylbenzothiadiazole-based chromophores

New two-photon up-conversion fluorescence (TPF) sensors, containing triphenylamine or carbazole as donor (D) and flanked pyridinylbenzothiadiazole as acceptor (A) to form D–π–An(n=1, 2 or 3) architecture, were synthesized and characterized. The investigation correlated molecular structure (acceptor number) with linear absorption, one-photon fluorescence (OPF) and two-photon fluorescence (TPF) detecting Cu2+, Ni2+, Hg2+ and Ag+ was carried out. Sensors containing more acceptor groups were found to exhibit greater sensitivity to both absorption and fluorescence detection. A comparison between OPF and TPF responses to the given metal ion (Cu2+) showed that the sensitivity of TPF quenching is larger than that of OPF quenching. This strongly supports the idea that pyridinylbenzothiadiazole-based chromophores with more acceptor groups possess potential application as two-photon up-conversion sensors.

Theory and experiments of Bragg cavity modes in passive and active metallic nanoslit array devices

Metallic nanoslit arrays exhibit several unique, surprising, and useful properties, such as resonant enhanced transmission and resonant local field enhancements. Here we present both a theoretical study of these static properties, as well as experiments showing the utilization of these features combined with active optical media. We develop an approximated, simple closed-form model for predicting and explaining the general emergence of enhanced transmission resonances through metallic gratings, in various configurations and polarizations. This model is based on an effective index approximation and it unifies in a simple way the underlying mechanism of all forms of enhanced transmission in such structures as emerging from standing wave resonances of the different diffraction orders of periodic structures. The known excitation of surface plasmon polaritons or slit cavity modes emerges as a limiting case of a more general condition. We also use this understanding of the resonant behavior of nanoslit arrays to design and fabricate such structures with embedded nanocrystal quantum dots, and show beaming of nonclassical light to a narrow angle of less than 4 deg, as well as an enhancement of the two-photon upconversion fluorescence process by a factor of ∼400.

CdSe/AsS Core−Shell Quantum Dots: Preparation and Two-Photon Fluorescence

Arsenic(II) sulfide (AsS)-coated CdSe core-shell nanocrystals can be prepared by a cluster-complex deposition approach under mild conditions. At 60 degrees C, growth of an AsS shell onto a CdSe nanocrystal can be realized through the crystallization of a cluster complex of AsS/butylamine in a mixed solvent of isopropanol/chloroform. The new, type I core-shell nanocrystal exhibits markedly enhanced one-photon fluorescence as well two-photon upconversion fluorescence. The nanocrystals can be used for infrared-excited upconversion cellular labeling.

Upconverted fluorescence in Nd3+-doped barium chloride single crystals

Upon excitation at 796 nm, Nd3+-doped BaCl2 single crystals show several upconverted fluorescence bands in the visible spectral range,with the most intense bands at 530, 590 and 660 nm, in addition to the typicalfluorescence bands in the infrared spectral range. The power dependence of the infraredfluorescence and the two-photon upconversion fluorescence intensities as well asthe corresponding radiative lifetimes have been investigated. No ‘saturation’ ofthe fluorescence intensities was observed upon increasing the excitation power.

Multiphoton Upconversion Fluorescence Properties of Heteroaromatic Push-Pull Polymer

Two novel heteroaromatic push-pull fluorescence polymers poly [(2,5-diphenylene-1,3,4-oxadiazole) -4,4′-vinylene-alt-N,N′-bis(4-phenylenevinylene) -phenylamine](P1) and poly [(2,5-diphenylene-1,3,4-oxadiazole) -4,4′-vinylene-alt-N-ethyl-3,6-carbazolevinylene](P2) were synthesized by the Wittig reaction and the Heck reaction. Polymers P1 and P2 have decomposition temperatures of 373 and 412 ℃,respectively,and exhibit good thermal stabilities. Their electrochemical properties were explored by cyclic voltammetry. The highest occupied molecular orbital(HOMO) energy levels of P1 and P2 were-5.39 and-5.81 eV,respectively,and the lowest unoccupied molecular orbital(LUMO ) energy levels of P1and P2were-2.81 and-3.09 eV,respectively. Three-photon and two-photon upconversion fluorescence spectra of both polymers were measured using a femtosecond Ti:sapphire that was pumped by a femtosecond laser at 1250 and 800 nm. Strong three-photon upconversion fluorescence with maximum emission wavelengths of 510 nm for P1 and 491 nm for P2 in THF solution were observed. By pumping at 800 nm,strong two-photon upconversion fluorescences at 511 nm for P1 and 495 nm for P2 in THF were measured. Maximum peaks of single-photon fluorescence in THF were at 503 nm for P1 and at 475 nm for P2 with fluorescence quantum yields of 0.80 for P1 and 0.31 for P2. The effect of solvent polarity on multi-photon fluorescence was studied. Increased solvent polarity were found to induce a marked red-shift of the emission band in polymers P1 and P2.

Optical parameters and upconversion fluorescence in Tm3+/Yb3+-doped alkali-barium-bismuth-tellurite glasses

Tm3+/Yb3+-doped alkali-barium-bismuth-tellurite (LKBBT) glasses have been fabricated and characterized. Density, refractive index, optical absorption, absorption and emission cross-sections of Yb3+, Judd–Ofelt parameters and spontaneous transition probabilities of Tm3+ have been measured and calculated, respectively. Intense blue three-photon upconversion fluorescence and near-infrared two-photon upconversion fluorescence were investigated under the excitation of a 980nm diode laser at room temperature. Wide infrared transmission window, high refractive index and strong blue three-photon upconversion emission of Tm3+ indicate that Tm3+/Yb3+ co-doped LKBBT glasses are promising upconversion optical and laser materials.

Synthesis and properties of a new two-photon absorbing chromophore

This paper presents of a new, conjugated and symmetric multi-branched two-photon absorption chromophore 1,2,4,5-tetrakis(4- N-methyl- N-hydroxyethylamino)vinylphenyl benzene (TKAVPB) with D-π-D structure. The new dye built on 1,2,4,5-benzene core with four amino-branching units, which allows efficient π-electron delocalization, exhibits moderate two-photon absorption (TPA) value in the femtoseconds regime (TPA cross-section as 97 × 10 −50 cm 4 s photon −1 molecule −1 with 200 fs laser pulses). Linear absorption, single and two-photon fluorescence spectra were experimentally studied. When pumped with 760 nm laser irradiation, TKAVPB shows strong two-photon up-conversion fluorescence with peak at 527 nm.

Intense blue upconversion fluorescence of Tm3+/Yb3+-codoped bismuth tellurite glasses

In this paper, Tm3+/Yb3+-codoped bismuth tellurite glasses with high refractive index have been synthesized. The refractive index of Tm3+/Yb3+-codoped bismuth tellurite glasses were measured by Metricon 2010 prism coupler at two wavelengths, and the values n1=2.0365 at 632.8nm and n2=1.9795 at 1550nm were obtained. The absorption spectra, fluorescence spectra and infrared transmittance spectra of this glass were measured and analyzed. Based on Judd-Ofelt theory, and intensity parameters Ωt(t=2，4 and 6) were obtained to be 3.90×10-20, 2.03×10-20 and 9.03×10-21cm2, respectively. Then the radiative transition probabilities, radiative lifetimes and fluorescence branching ratio were calculated. Intense blue three-photon upconversion fluorescence and near-infrared two-photon upconversion fluorescence were investigated under the excitation of 980nm diode laser at room temperature. Wide infrared transmission window, high refractive index and strong blue three-photon upconversion emission of Tm3+ indicate that Tm3+/Yb3+-codoped LKBBT glasses are promising upconversion optical and laser materials.

Temporal and spectral behaviors of two-photon induced emission laser dyes

The temporal and spectral properties of two-photon induced fluorescence and up-conversion lasing of two new laser dyes have been experimentally investigated. Pumped by 1064 nm mode-locked Nd:YAG laser, effective two-photon induced fluorescence with peak wavelength at 635 nm and up-conversion lasing at ∼626 nm emitted from the solutions of these new dyes in DMF. The lifetimes of two-photon up-conversion fluorescence of the two dyes are 65 and 67 ps. At picosecond laser pumping, the efficiency of up-conversion lasing is 8.4% and 9.1% for the two new dyes.

STUDY ON UP-CONVERSION LUMINESCENCE RESEARCH OF TmP5O14 CRYSTAL

The up-conversion luminescence phenomenon of TmP5O14 crystal at room temperature pumped by pulsed DCM dye laser is studied. It is found that there appear strong 450 and 360 nm and weak 347 nm fluorescences. Through careful experiment al investigation and theoritical analysis, we find that the 450 and 360 nm radiations are 1D2→3F4,3H6 two-photon upconversion fluorescence and 347 nm radiation is 1I6→3F4 three-photon fluorescence. The up-conversion process can be elucidated as follows: when a Tm3+ ion absorbs a first pumping photon and reaches the 3F2 state from the 3H6 bound state, the population of 3F2 state falls down rapidly to the 3H4, state due to the rather strong nonradiative relaxation. Then the excited state absorption from 3H4 to 1D2 takes place and the 360 nm two-photon up-conversion fluorescence from 1D2 state is appears. Meanwhile, there is a small possibility for energy transfer between 1D2 state and 3H4 state. It results in a converted population with respect to the 1I6 state and the 347 nm three-photon up-conversion fluorescence is appear, the up-con-version mechanism of which is a complicated process involving both the excited state absorption and the temperature of photons.