Bright Blue Upconversion Research Articles

Green, room-temperature, fast route for NH4Yb2F7:Tm3+ nanoparticles and their blue upconversion luminescence properties

Abstract A pure ammonium fluorolanthanate NH4Yb2F7 matrix and its derivative doped Tm3+ were successfully synthesized by an ultra-fast solution route at room temperature. The as-prepared nanoparticles (NPs) were about 70 nm in diameter with the uniform size. In addition, NH4Yb2F7:Tm NPs demonstrated a bright blue upconversion luminescence feature, which can be observed with the naked eye. There are five emission bands in the range of 400–800 nm and the primary blue and red bands derived from the transitions of 1D2→3F4 and 1G4→3F4, respectively. The blue emission was populated via a three-photon process based on the relationship between emission intensity and excitation pump power. Our ultra-fast synthesis route presents a green and one-step strategy for the large-scale production. Moreover, the excellent blue upconversion will arouse extensive interest in upconversion studies in ammonium fluorolanthanate based hosts and pave the way for further development of upconversion material family.

Up-conversion of Nd3+/Yb3+/Tm3+ tri-doped CaTeO3 compound under excitation of 808 nm

Nd3+/Yb3+/Tm3+ tri-doped CaTeO3 compounds were prepared by a solid-state reaction method. Bright blue up-conversion (UC) luminescence at around 476 nm, which corresponds to the Tm3+: 1G4 → 3H6 transition, was observed under 808-nm excitation. The Nd3+ → Yb3+ → Tm3+ energy transfer process was responsible for the strong blue up-conversion emission in the tri-doped phosphor. The Tm3+ blue up-conversion emission intensity was strongly dependent on the concentrations of Yb3+ and Nd3+. The possible up-conversion mechanisms for the Nd3+/Yb3+/Tm3+ tri-doped CaTeO3 phosphor are discussed, based on the Nd3+ and Yb3+ concentration-dependent UC spectra, near-infrared luminescence spectra and luminescence decay curves.

Anticancer Effects and Cell Death Pathways in Ultralow-Power 980 nm Laser-Triggered Photodynamic Therapy by Gd₂O₃:Yb, Tm Nanoparticles.

Upconverting Gd₂O₃:Yb, Tm nanoparticles that can provide photodynamic therapy (PDT) for cancer cells upon 980 nm near-infrared (NIR) laser irradiation are prepared. The nanoparticles emit bright blue upconversion fluorescence (470∼520 nm) when excited by a 980 nm laser. A well-selected PDT drug, merocyanine 540 (MC540), which shows an absorption maximum within the 495∼540 nm band, is loaded onto the surface of the nanoparticles to obtain Gd₂O₃:Yb, TmMC540. A prominent PDT-induced killing effect on both human cervical cancer cells (HeLa cells) and human hepatocellular liver carcinoma cells (HepG2 cells) is achieved under 980 nm laser irradiation at a very low power density of 0.65 W cm-2, which is lower than The American National Standard for the safe use of 980 nm lasers (0.72 W cm-2. The cell death modes are further studied in detail via a uranyl acetate section-staining method to analyze the morphological cell changes before and after PDT. With clear evidence of mitochondrial damage, chromatin condensation and the formation of apoptotic bodies, an apoptosis mechanism is confirmed to be responsible for both HeLa and HepG2 cell death in Gd₂O₃:Yb, Tm-MC540-mediated PDT. Due to excessive damage, the cancer cells are efficiently killed, and autophagy is found to be initiated immediately after PDT.

Color-tunable up-conversion emission of luminescent-plasmonic, core/shell nanomaterials – KY3F10:Yb3+,Tm3+/SiO2-NH2/Au

Multifunctional luminescent-plasmonic KY3F10:Yb3+,Tm3+/SiO2-NH2/Au nanomaterials were successfully obtained. The lanthanide-doped fluoride nanoparticles (NPs), synthesized under hydrothermal conditions exhibited bright blue up-conversion luminescence (λex=980nm). Such lanthanide nanocrystals (20–40nm) were coated with amine modified silica shell, forming core/shell nanostructures. Their surface was further uniformly covered with ultra-small gold NPs (4–7nm). The as-prepared luminescent-plasmonic core/shell nanomaterials exhibited tunable up-conversion emission, due to the interactions between plasmonic and luminescent phases. The emission of Tm3+ ion was affected by the surface Au NPs, which exhibited strong plasmonic absorption in the visible range (450–650nm). The increasing amount of the surface Au NPs, led to the significant alterations in a ratio of the Tm3+ emission bands. The NIR band (3H4→3H6) was unchanged, whereas the ratio and relative intensity of the bands in a visible range (1G4→3H6 and 1G4→3F4) was altered. This led to the significant change of the emission spectra shape and influenced color of emission, tuning it from bright blue to blue-violet. The products obtained were characterized by transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), powder X-ray diffraction (XRD), UV–vis absorption spectroscopy and luminescence spectroscopy (excitation/emission spectra and luminescence decay curves).

Water-soluble Yb 3+, Tm 3+ codoped NaYF 4 nanoparticles: Synthesis, characteristics and bioimaging

Water soluble NaYF 4 nanocrystals codoped with 20 mol% Yb 3+, 0.5 mol% Tm 3+ were prepared by a facile solvothermal approach using polyvinylpyrrolidone (PVP) as a surfactant. The upconversion NaYF 4 nanocrystals were pure cubic phase with an average size of ∼40 nm. They could be well redispersed in water to form a clearly transparent solution without obvious precipitation. With the excitation of a 980-nm diode laser, the nanocrystal solution presents bright violet and blue upconversion luminescence. These upconversion nanoparticles (UCNPs) were incubated with HeLa cells at 37 °C for 24 h, and bright blue upconversion luminescence were observed from the UCNPs endocytosed into the HeLa cells on a microscope equipped with a 980-nm fiber laser. These results indicated that the UCNPs had potential applications for biological imaging as luminescent probes.

Synthesis and Upconversion Luminescence of NaYF4:Yb3+,Tm3+/TiO2 Nanocrystal Colloidal Solution

NaYF4:Yb3+,Tm3+ upconversion nanocrystals were synthesized with oleic acid as a capping ligand. The as-prepared samples were redispersed in cyclohexane, forming transparent and stable solutions which perform bright blue upconversion. Inducing TiO2 as the outer layer of the fluoride cores, we investigated the effect of TiO2 on the upconversion process. The transmission electron microscopy (TEM) analysis indicated that titania successfully formed a coating layer on the surface of NaYF4:Yb3+, Tm3+ nanoparticles, and the average diameters of the NaYF4:Yb3+,Tm3+ nanocrystals and the NaYF4:Yb3+, Tm3+/TiO2 nanoparticles are about 14 and 40 nm, respectively. Under the excitation of a 980 nm laser, NaYF4:Yb3+, Tm3+ nanocrystals and TiO2-coated NaYF4:Yb3+, Tm3 core/shell structure sample exhibited distinct upconversion luminescent properties.

Photoluminescence of Pr3+-, Dy3+- and Tm3+-doped transparent nanocrystallized KNbGeO5 glasses

In this paper, we present the photoluminescence properties of Pr3+-, Dy3+- and Tm3+-doped potassium–niobium–germanate glasses and glass ceramics. From the x-ray diffraction measurement, the glass structure was established. These glasses have shown strong absorption bands in the near-infrared region. Compared with Pr3+-, Dy3+- and Tm3+-doped glasses, their respective glass ceramics have shown stronger emissions due to the presence of the K3.8Nb5Ge3O20.4 crystalline phase. For Pr3+ -doped glass, two weak emission bands centred at 616 nm(3P0 → 3H6) and 648 nm(3P0 → 3F2) and for glass ceramic strong emission bands centred at 533 nm(3P0 → 3H5), 616 nm(3P0 → 3H6) and 648 nm(3P0 → 3F2) along with weak emissions at 688 nm(3P1 → 3F3), 709 nm(3P0 → 3F3) and 732 nm(3P0 → 3F4) have been observed with 450 nm(3H4 → 3P2) excitation wavelength. Among them, 648 nm(3P0 → 3F2) has shown bright red emission. For the Pr3+ -doped glass and glass ceramic, upconversion emission spectra have also been measured. Bright blue upconversion luminescence was observed under 1D2 level excitation. With regard to Dy3+ : glass, a weak emission band centred at 576 nm(4F9/2 → 6H13/2) and for glass ceramic a blue emission band centred at 485 nm(4F9/2 → 6H15/2) and a bright fluorescent yellow emission at 576 nm(4F9/2 → 6H13/2) have been observed, apart from 4F9/2 → 6H11/2(664 nm) emission transition with an excitation at 389 nm(6H15/2 → 4I13/2, 4F7/2) wavelength. Emission bands of 1G4 → 3F4(650 nm), 3F3 → 3H6(707 nm) and 1G4 → 3H5(774 nm) transitions have been observed for the Tm3+ : glass and glass ceramic, with an excitation at 3H6 → 1G4(473 nm). Among them, the 1G4 → 3F4 transition (650 nm) shows bright red emission. The stimulated emission cross-sections of all the emission bands of Pr3+, Dy3+ and Tm3+ : glasses and glass ceramics have been computed based on their measured full width at half maximum (Δλ) and lifetimes (τm).

Blue Cooperative Luminescence In Yb3+-Doped Barium Gallogermanate Glass Excited At 976 nm

The Yb3+-doped barium gallogermanate glass has been prepared via the conventional melt method. The absorption spectra, the near infrared emission spectra, the upconversion emission spectra and the differential scanning calorimetry have been measured. Bright blue upconversion emission centered at 476 nm has been observed under the 976 nm laser diode excitation at room temperature. The blue upconversion emission mechanism has been discussed on the blue emission intensity and the measured lifetime. The slope of the log-log plot of the blue emission intensity versus the pump power is equal to 1.98, and the blue luminescence decay time is half of the near infrared fluorescence decay time, confirming that the blue emission comes from Yb3+-Yb3+ pairs cooperative upconversion mechanism. The result of differential scanning calorimetry suggests that this type of glass is suitable as a potential candidate for fiber drawing.

Phonon-assisted mechanisms and concentration dependence of Tm3+ blue upconversion luminescence in codoped NaY(WO4)2 crystals

Optical parameters of NaY(WO4)2 crystals were calculated from absorption spectra with Judd–Ofelt theory. Intensive infrared-to-visible frequency upconversion has been discovered and investigated under a 974 nm CW laser diode excitation at room temperature. The bright blue upconversion fluorescence emission is analysed in detail. The optimal concentration of Tm3+, which is about 1 at% for a Yb3+ concentration of 10 at% for the blue emission in the crystals, is much higher than that in other hosts. The experimental results and theoretical analysis suggest that NaY(WO4)2 with high phonon energy is most probably an even more promising crystal than fluoride.

Sensitized thulium blue upconversion emission in Nd3+/Tm3+/Yb3+ triply doped lead and cadmium germanate glass excited around 800 nm

Bright blue upconversion emission by thulium ions in PbGeO3–PbF2–CdF2 glass triply doped with Nd3+–Tm3+–Yb3+ under diode laser excitation around 800 nm is reported. The results revealed that the Nd3+/Tm3+/Yb3+-codoped sample generated ten times more 475 nm blue upconversion fluorescence than the Yb3+-sensitized Tm3+-doped one, under the same excitation power. The upconversion process also showed a strong dependence upon the Yb3+ concentration. The results also indicated that the neodymium ions played a major role in the upconversion process by transfering the 800 nm excitation to thulium ions. The population of the Tm3+ ions G41 emitting level was accomplished through a multiion interaction involving ground-state absorption of pump photons around 800 nm by the Nd3+(4I9/2→2H9/2, 4F5/2) and Tm3+(3H6→3F4) ions followed by energy-transfer processes involving the Nd3+–Yb3+(4F3/2, 2F7/2→4I11/2, 2F5/2) and Yb3+–Tm3+(2F5/2, 3F4→2F7/2, 1G4) pairs.