Upconversion Fluorescence Spectra Research Articles

One- and Two-Photon Photophysical Properties, Ultrafast Dynamics, and DFT Study of Three Modified Zinc Phthalocyanines.

As two-photon absorption (TPA) materials, phthalocyanine molecules have promising application prospects due to their large TPA absorption cross-section, high third-order nonlinear optical susceptibility, and ultrafast response characteristics. In this work, optical properties and the ultrafast response of three modified zinc phthalocyanine molecules (P-HPcZn, Pc-P-Pc, and (DR1)4PcZn) were analyzed. No obvious side-shoulder absorption peaks in the Q-band can be observed from the steady-state absorption spectra of the three molecules, confirming the lack of aggregation products in the solutions of our measurement. Open-aperture Z-scan results show relatively large TPA cross-section values of 136.4 and 55.3 GM for Pc-P-Pc and (DR1)4PcZn, respectively. The nonlinear optical results show that the absorption process observed under the excitation of femtosecond pulses is a reverse saturable absorption (RSA) mechanism. Up-conversion fluorescence spectra of (DR1)4PcZn in THF solution indicate that the fluorescence emission mechanism is TPA. In the study of ultrafast dynamics, the transient absorption spectra were investigated and the decay lifetime of the dynamic traces corresponding to some representative probe wavelengths was obtained through data fitting with a multi-exponential function. Finally, the charge transfer and excited state properties of the modified zinc phthalocyanine molecules were discussed in depth by the DFT method. The energy gaps of P-HPcZn, Pc-P-Pc, and (DR1)4PcZn are 2.16, 1.39, and 2.13 eV, respectively. The results indicate that the Pc-P-Pc of donor-acceptor-donor (D-A-D) structure has the smallest energy gap as well as the best charge transfer properties.

NaYF4:Yb3+/Ho3+ up-conversion luminescence and its low temperature sensing characteristics

Pure hexagonal [Formula: see text]-NaYF4 micron crystals were synthesized by the hydrothermal method with the up-conversion luminescence properties studied by doping Yb[Formula: see text]/Ho[Formula: see text]. The up-conversion fluorescence spectra and fluorescence lifetime of [Formula: see text]-NaYF4 micron crystals were determined by FLS-980 transient fluorescence spectrometer. By changing the doping concentration of Yb[Formula: see text]/Ho[Formula: see text], the optimal doping concentration was confirmed to be 20%Yb[Formula: see text]/2%Ho[Formula: see text]. The fluorescence spectrum was obtained by changing pump power, the relationship between power and intensity was analyzed, and the [Formula: see text]-NaYF4 micron crystal green and red emission up-conversion process was obtained into a two-photon process. The 5F[Formula: see text]I8 and 5S[Formula: see text]I8 of the sample were thermally coupled to obtain a large absolute sensitivity (Sa) of low temperature. The maximum absolute sensitivity within the range of 64–194[Formula: see text]K is 0.0097[Formula: see text]K[Formula: see text] at 144[Formula: see text]K, while maximum absolute sensitivity at 333[Formula: see text]K is 0.00335[Formula: see text]K[Formula: see text] in the range of 293–493[Formula: see text]K. The experimental results show that the sensing characteristics of [Formula: see text]-NaYF4:Yb[Formula: see text]/Ho[Formula: see text] at low temperature are better than those at high temperature, and it has the potential to be used in the field of temperature sensing.

Light-driven upconversion fluorescence micromotors

Light-driven micromotors with high spatial resolution are powerful tools for targeted drug delivery and biomedical diagnosis. To combine the function of biosensing, light-driven micromotors have been modified with fluorescence materials such as quantum dots or dyes. However, these fluorescence micromotors are generally driven and excited by ultraviolet or visible lights, which may cause photo-damage to biological cells or tissues. Here we propose upconversion fluorescence micromotors (UCFMs) constructed by lanthanide (NaYF4: Yb3+, Er3+) doped microrods that were driven and excited by near-infrared lights. The UCFMs were moved to the surfaces of the targeted cancer cells using scanning optical tweezers (SOTs). The upconversion fluorescence spectra were measured to determine the temperatures of the cells, with an absolute sensitivity from 1.71 × 10−3 to 1.74 × 10−3 K−1 and a relative sensitivity from 0.53% to 0.68% K−1. The UCFMs were then optically driven to actuate the local flow to deliver the polystyrene (PS) microparticles and doxorubicin-loaded mesoporous silica nanoparticles to the vicinity of the cancer cells. By integrating the actuator and sensor into a single device, the UCFMs hold great potential for applications to precise biosensing, single-cell biomedical analysis, and targeted drug delivery.

Effect of annealing temperature on optical properties of Erbium doped Y2Zr2O7 transparent ceramics

Through the vacuum sintering method, Erbium-doped Y2Zr2O7 transparent ceramics were successfully fabricated. The obtained ceramics were annealed at different temperatures and the relationship between annealing temperature and sample structure was investigated to reveal the effect of oxygen vacancy. Y1.98Er0.02Zr2O7 ceramics annealed at 800 °C starts to be transparent and when added up to 900 °C, samples show the highest transmittance over 76% in the near-infrared (NIR) region. Then the transmittance gradually decreased to 71% with the increase of annealing temperature. XRD and SEM measurements were performed to characterize the crystal structure and microstructure of Er3+: Y2Zr2O7 as-prepared powders and ceramics. The excitation spectra display that Y1.98Er0.02Zr2O7 ceramics can be effectively excited by 382 nm. When the annealing temperature exceeds 700 °C, two strong green emission bands and one red emission band can be observed in both up-conversion (UC) and down-conversion (DC) fluorescence spectra. Our results suggest that annealing temperature has a great impact on the structure and optical properties of Er3+: Y2Zr2O7 ceramics, which is significant for fabricating ceramics with better optical properties.

Excitation wavelength dependent photoluminescence and photochromic studies of Yb3+/Er3+ doped β−KYF4 and β−NaYF4 nanoparticles

We report both resonant and off-resonant laser excitation of Er3+ upconversion fluorescence and colour tunability in Er3+/Yb3+ co-doped KYF4 and NaYF4 nanoparticles. The nanoparticles were prepared using a hydrothermal method with particle sizes of 74 ± 20 nm and 345 ± 91 nm for β−KYF4 and β−NaYF4, respectively. The Yb3+ 2F7/2 → 2F5/2 absorption spectra exhibit absorption maxima at 10237 cm−1 (977 nm) for β−NaYF4 and 10267 cm−1 (974 nm) for β−KYF4 nanoparticles. The Er3+ upconversion fluorescence spectra consist of the 2H11/2,4S3/2, and 4F9/2 → 4I15/2 transitions for either 974, 977 or 980 nm laser excitation in both materials. We observed an enhancement in the upconversion intensity by a factor of up to 20 for β−KYF4 and 1.5 fold for β−NaYF4 under resonant excitation compared with off-resonant excitation at 980 nm. Tuneable upconversion fluorescence wavelength was achieved in β−KYF4:Yb/Er nanoparticles by adjusting the excitation wavelength. The CIE chromaticity coordinates are (0.6836, 0.3151) with a highest red colour purity of 99.70% for β−KYF4 (4700 K) and (0.3953, 0.5915) with a colour purity of 96.84% for β−NaYF4 (4533 K) nanoparticles. The respective absolute upconversion quantum yields are 1.18% and 2.34% under low power density (1.65 W⋅cm−2).

The sensitization and deactivation effects of Nd3+ ion in Nd,Ho:CaYAlO4 disordered crystal for 2.86 µm tunable and ultrafast laser

Nd,Ho:CaYAlO4 (Nd,Ho:CYA) crystals with two different Nd3+ doping concentrations for ∼3 µm mid-infrared (MIR) laser were grown successfully by the Czochralski method. The sensitization and deactivation effects of Nd3+ ions were analyzed based on the polarized absorption spectra, mid-infrared and upconversion fluorescence spectra and fluorescence decay curves in detail. Excited by 808 nm laser diode (LD), strong 2.86 µm emission was observed. The maximum emission cross section was calculated to be 1.93 × 10-20 cm2 in 1.0 at.% Nd, 2.5 at.% Ho:CYA, and the FWHM was about 115 nm. The ∼3 µm emission was enhanced by 10 times compared to the 2.5 at.% Nd, 2.5 at.% Ho:CYA crystal. Due to the dual function of Nd3+ as effective sensitizing and deactivating ion, 1.0 at.% Nd, 2.5 at.% Ho:CYA had a relatively longer lifetime 0.240 ms for the upper level 5I6, while the lifetime of the lower level 5I7 reduced to 0.723 ms, which was greatly advantageous to the population inversion. The calculated deactivation efficiency from Ho3+: 5I7 to Nd3+: 4F13/2 was estimated to be 89.66%. All results indicated that 1.0 at.% Nd, 2.5 at.% Ho:CYA crystal is a promising gain medium for ∼3 µm tunable and ultrafast laser output under 808 nm LD pump.

Facile Synthesis of NaYF4:Yb Up-Conversion Nanoparticles Modified with Photosensitizer and Targeting Antibody for In Vitro Photodynamic Therapy of Hepatocellular Carcinoma.

Rare Earth up-conversion nanoparticles NaYF4:20%Yb,2%Er@PEI (UCNPs) were generated via a one-step hydrothermal technique at relatively reduced temperatures. Photosensitizer Ce6 and anti-EpCAM, a highly expressed monoclonal antibody in cancer stem cells of hepatocellular carcinoma, were linked to UCNP surfaces via the formation of amide linkage between carboxyl from Ce6 or anti-EpCAM and abundant amino from PEI, leading to the formation of Ps-Ce6 and anti-EpCAM-UCNPs-Ce6 nanoparticles. The synthesized nanoparticles characterized by XRD, TEM, and IR, and their zeta potential, ROS generation ability, Ce6 loading rate, and up-conversion fluorescence properties were investigated. It has been revealed that all the products were uniformly dispersed nanoparticles (25–32 nm), which crystallized primarily as hexagonal structures, and their up-conversion fluorescence spectra were similar to that of NaYF4:20%Yb,2%Er. The Ce6 loading rate in the anti-EpCAM-UCNPs-Ce6 nanoparticles was about 2.9%, thereby resulting in good ROS generation ability. For anti-EpCAM-UCNPs-Ce6, the biosafety, targeting effect, and PDT effect exposed under near-infrared (NIR) laser (980 nm) were evaluated using human liver cancer cells (BEL-7404). The results showed that it has good biocompatibility and biosafety as well as high targeting and PDT treatment efficiencies, which renders it a potential experimental material for the near-infrared PDT study.

Growth and spectroscopy of Er: LuYO3 single crystal

A 5 at% Er: LuYO3 crystal was grown by optical floating zone method for the first time. The absorption section at 980 nm is 0.35×10−20cm2 with FWHM of 19 nm. The intensity parameters Ωi(i=2,4,6) and the radiative transition probability, fluorescence branching ratio and lifetime of energy level transition from 4I11/2 to 4I13/2 and 4I13/2 to 4I15/2 of Er ion in Er: LuYO3 crystal were calculated. The emission cross-sections centered at 2721 nm and 1556 nm are 1.46 × 10−20 cm2 and 2.61 × 10−21 cm2, which correspond to the transitions of Er3+: 4I11/2→4I13/2 and Er3+: 4I13/2→4I15/2, respectively. The fluorescence lifetime of 4I11/2and 4I13/2 under the excitation of 980 nm pulsed LD were 2.29 ms and 7.84 ms, respectively. The up-conversion fluorescence spectra and fluorescence decay curves were measured. The potential utility of the Er: LuYO3 crystal as a tunable and ultra-short laser medium at 3.0 μm and 1.5 μm can be expected.

Калибровка температуры по нормированным спектрам АП-конверсионной флуоресценции германатных стекол и стеклокерамик, активированных ионами эрбия и иттербия

To select erbium and ytterbium doped germanate glasses and glass ceramics, which are most suitable as sensitive elements of fluorescent temperature sensors, a multivariate model of temperature calibration has been developed based on principal component analysis, cluster analysis and interval projection to latent structures of up-conversion green fluorescence spectra. The calibration model used 95 spectral variables for the GeO2-Na2O-Yb2O3-MgO-La2O3-Er2O3 glass-ceramic is characterized by the best quality parameters: the root-mean-square error is 0.37 K, the residual prediction deviation for the test subset is greater than 102, and the relative error does not exceed 0.20%.

Optical properties and luminescence of Er3+/Yb3+ co-doped La2O3–Nb2O5–Ga2O3 glasses prepared by aerodynamic levitation method

40La2O3–20Nb2O5–40Ga2O3 and xYb2O3–5Er2O3–(35-x) La2O3–20Nb2O5–40Ga2O3 (x = 0, 1, 5, 10) spherical transparent glasses were prepared by aerodynamic levitation method. Upconversion and near-infrared luminescence characteristics have been studied. Moreover, the thermal, mechanical, refractive index, transmittance properties of the glasses have also been discussed. Hardness and density of the glasses increase with the increase of Yb3+ concentration. The hardness of all samples are above 8.4 GPa, and density increase from 5.2504 g/cm3 to 5.817 g/cm3. The blank LNG glass has a refractive index of 2.0217 and Abbe number of 88.84, which is an excellent glass with high refractive index and low dispersion. Through DTA analysis, it is found that this series of glasses has excellent thermal stability. The glasses transition temperature (Tg) is about 800 °C. With the increase of Yb3+ concentration, Tg does not change obviously, but the crystallization initial temperature To and △T (△T = To−Tg) increase at first and then decrease. Upconversion fluorescence spectra show that green and red emission bands of 551 nm, 558 nm and 674 nm are obtained under the pump of 980 nm laser, which are two-photon emission processes. And in the near infrared region, the near-infrared emission with the emission center at 1559 nm is obtained, which corresponds to the transition from 4I13/2–4I15/2 of Er3+. The full width at half maximum (FWHM) of the prepared samples is about 120 nm, which is larger than that of ordinary glass. At the same time, with the increase of Yb3+ concentration, the change trend of fluorescence lifetime is consistent with that of near-infrared emission intensity.

Up-Conversion Nanoparticles/PMMA Composites for Light-Emitting Applications

In this paper, we prepared KMnF3:Yb[Formula: see text], Er[Formula: see text] nanoparticles (NPs)/polymethyl methacrylate (PMMA) composites, NaYF4:Yb[Formula: see text], Tm[Formula: see text]NPs/PMMA composites and NaYF4Yb[Formula: see text], Er[Formula: see text]NPs/PMMA composites by in situ polymerization, and these NPs/PMMA composites can emit red, blue and green up-conversion fluorescence excited by 980[Formula: see text]nm, respectively. The mixed white NPs/PMMA composites were obtained by adjusting the doping ratio of the above three NPs. These NPs/PMMA composites are transparent. We tested the up-conversion fluorescence spectra of all the NPs and NPs/PMMA composites, under 980[Formula: see text]nm excitation. The up-conversion luminescence spectra of the NPs and NPs/PMMA composites are consistent, which further indicates that the in situ polymerization has not changed the chemical structure of the NPs. Then, we prepared transparent bulk polymers by curing these NPs/PMMA composites. Under 980[Formula: see text]nm laser excitation, these NPs/PMMA bulk polymers can emit red, blue, green and white up-conversion emissions, respectively. The results indicate that the NPs/PMMA composites can be applied to three-dimensional (3D) display.

Effects of Er3+ concentration on the optical properties of Er3+:SrGdGa3O7 single crystals

High-quality single crystals of different Er3+ concentration doped SrGdGa3O7(SGGO) were grown successfully by the Czochralski method. The absorption, up-conversion, near-infrared and mid-infrared fluorescence spectra, as well as the fluorescence decay curves of Er:4I13/2 and 4I11/2 levels in Er:SGGO crystal were measured at room temperature. As the concentration of Er3+ ions increase, the spectra of Er:SGGO crystals show weaker near-infrared emission and stronger mid-infrared emission. The lifetime of the 4I13/2 state decreases by nearly 7times while the lifetime of the 4I11/2 state decreases by only about 1.3 times in the Er:SGGO crystals. These results indicate that the heavily Er3+ doped SGGO crystals is beneficial to improve the 2.7 μm laser.

An NIR-light-responsive surface molecularly imprinted polymer for photoregulated drug release in aqueous solution through porcine tissue.

The application of photoresponsive surface molecularly imprinted polymers based on azobenzene is limited by the UV light source required and their poor water solubility. Reducing the phototoxicity and solvent toxicity of the polymers therefore presents a challenge. In this work, an NIR-light-responsive surface molecularly imprinted polymer was fabricated by atom transfer radical polymerization using up-conversion nanoparticles as the core, a hydrophilic green-light-responsive azobenzene derivative as the functional monomer, and a drug as the template. The up-conversion nanoparticles core emitted green fluorescence in the range of 520-550 nm upon NIR irradiation (980 nm, 5 W cm-2), which was absorbed by the azobenzene containing molecularly imprinted polymers layer on the up-conversion nanoparticles surface. This caused the azobenzene chromophores to undergo trans→cis isomerization in phosphate buffered solution (pH = 7.4), thus resulting in NIR-light-induced drug release. The up-conversion fluorescence spectra were used to study the interaction mechanism between the azobenzene monomer and NIR light. Compared with structural analogues of the template (antifebrin and phenacetin), the NIR-light-responsive surface molecularly imprinted polymer showed excellent specificity of recognition for the template drug (paracetamol). The maximum adsorption capacity of the NIR-light-responsive surface molecularly imprinted polymer for loading of paracetamol was 16.80 μmol g-1. The NIR-light-responsive surface molecularly imprinted polymer was applied for NIR-light-induced paracetamol release in phosphate buffered solution (pH = 7.4) through porcine tissue. This work demonstrates the potential of drug delivery systems based on molecularly imprinted polymers for application in deep tissue delivery.

Spectroscopic properties and rate equation model of Er doped BaLaGa3O7 crystals

Single crystals of pure and Er3+ doped BaLaGa3O7 were grown successfully by the Czochralski technique. The absorption spectra, emission spectra including up-conversion, near-infrared and mid-infrared fluorescence spectra, as well as the fluorescence decay curves were measured at room temperature. The optical parameters of absorption and emission cross sections, the fluorescence lifetimes were evaluated and compared. Based on the Judde-Ofelt theory, Judde-Ofelt parameters such as the fluorescent branching ratios, the spontaneous transition probabilities and the radiative lifetimes were calculated. According to the energy transfer diagram, the rate equation model was built and discussed. In summary, Er3+: BaLaGa3O7 crystal is attractive and significant as laser gain material for realization of ∼2.7 μm laser output.

Structural and fluorescence properties of Ho3+/Yb3+ doped germanosilicate glasses tailored by Lu2O3

Structural and fluorescence properties of Ho3+/Yb3+ co-doped germanosilicate glasses have been modified by tailoring the composition using lanthanide additive Lu2O3. Raman spectra and X-ray Photoelectron spectra reveal that the addition of Lu2O3 can change the structure by increasing non-bridging oxygens (NBO) in this glasses. Meanwhile, an improved thermal stability (ΔT: from 110 to 187 °C) has also been obtained via Lu3+ ‘lanthanide contraction’. Futhermore, the positive effect of changed glass structure gives excellent fluorescence properties by the decreasing cross relaxation process which are proved by the experimental upconversion, near-infrared and mid-infrared fluorescence spectra. Additionally, a double enhancement of a 2.0 μm emission has been achieved successfully in this silica-germanate glass with 7 mol% Lu3+ addition, which possesses a larger emission cross section (4.41 × 10−21 cm2) at 2022 nm. These results indicate that the optimized emission of Ho3+ for optical fiber laser can be achieved by tuning the glass structure using lanthanide additive Lu2O3.

Structural and photoluminescence properties of Yb/Tm co-implanted ZnO crystals

ZnO virgin crystals were implanted with keV Yb and Tm ions at a total fluence of ~1015ions/cm2 at 600°C. Thermal annealing was performed at 800°C for 30min in oxygen ambient. The effects of ion irradiation on the structural properties of the crystals were investigated using Rutherford backscattering/channeling and high-resolution X-ray diffraction technique. Near-infrared and upconversion luminescence emissions were demonstrated under excitation with 532 and 980nm lasers, respectively. Results showed that the upconversion fluorescence spectra consisted of two emission peaks at around 484 and 673nm, which were assigned to the Tm3+:1G4→3H6 and Tm3+:1G4→3F4 transitions, respectively.

Growth, structure and spectroscopic properties of melilite Er: CaLaGa 3 O 7 crystal for use in mid-infrared laser

Abstract Single crystals of pure and Er 3+ doped CaLaGa 3 O 7 were firstly grown by the Czochralski technology. The structure of CaLaGa 3 O 7 was investigated. The electronic structures of CaLaGa 3 O 7 crystal were performed by using first-principles calculations based on density functional theory (DFT) methods. Its band structure and density of states were presented. The polarized absorption, emission spectra including up-conversion, near-infrared and mid-infrared fluorescence spectra, as well as the fluorescence decay curves of Er: CaLaGa 3 O 7 crystal were measured at room temperature. Detailed spectroscopic analyses of Er: CaLaGa 3 O 7 were carried out. Based on the Judd–Ofelt theory and the polarized absorption spectra, the spontaneous transition probabilities, the fluorescent branching ratios and the radiative lifetimes were calculated. The energy transfer mechanism in Er: CaLaGa 3 O 7 crystal was also studied in this work. It concludes that Er: CaLaGa 3 O 7 crystal can act as a promising candidate for mid-infrared lasers.

Effect of erbium concentration on optical properties of Er:YLF laser crystals

Four Er-doped LiYF4 crystals with different Er-concentrations were grown by Czochralski method. The laser crystals were characterized by measurements of ICP-AES, XRD, absorption spectra, up-conversion fluorescence spectra, near-infrared (NIR) and mid-infrared (Mid-IR) fluorescence spectra, as well as luminescence decays. It was found that the heavily 15at% Er-doped YLF crystal is more proper in up-conversion or ∼3μm laser applications; while the 5at% Er-doped YLF is a better candidate for ∼1.5μm lasers within these four crystals.

Intense upconversion fluorescence in Tm 3+/Yb3+ codoped alumina lead borate glasses

The Tm3+/Yb3+ codoped alumina lead borate glasses were prepared by the conventional melt quenching technique. Optical absorption and FTIR spectra were recorded. The upconversion fluorescence spectra exhibited weak blue (480 nm) and intense red (660 nm) emissions due to 1G4 → 3H6 and 1G4 → 3H4 transitions, respectively. The results concluded that both emissions are due to three photon absorption process. It has been observed that in the upconversion efficiency increases with the increase in the concentration of Yb3+ ions. The strong red upconversion fluorescence indicate that Tm3+/Yb3+ codoped alumina lead borate glasses can be used as potential host material for upconversion lasers.

A novel ECL sensor for determination of carcinoembryonic antigen using reduced graphene Oxide-BaYF5:Yb, Er upconversion nanocomposites and gold nanoparticles

We reported a novel ECL immunosensor for detection of carcinoembryonic antigen (CEA) based on the reduced graphene Oxide-BaYF5:Yb, Er (rGO-BaYF5:Yb, Er) nanocomposites. The rGO-BaYF5:Yb, Er nanocomposites, used as electrode luminescence materials, were prepared by in situ hydrothermal method, and characterized by TEM, XRD, UV–vis spectra, and upconversion fluorescence spectra. Further, poly (diallyldimethylammonium chloride) (PDDA), Au nanoparticles (AuNPs), and Anti-CEA were successively assembled on the surface of rGO-BaYF5:Yb, Er nanocomposites modified-electrode for fabricating ECL immunosensor. The results of the ECL measurements of CEA indicated that this novel ECL immunosensor exhibited high sensitive response to CEA in a linear range of 0.001–80ngmL−1 with a low detection limit of 0.87pgmL−1, good selectivity and satisfactory stability.