- Upconversion luminescence in sub-10 nm β-NaGdF4:Yb3+,Er3+ nanoparticles: An improved synthesis in anhydrous ionic liquids
-
Sub-10 nm β-NaGdF4:18% Yb3+,2% Er3+ nanoparticles were synthesized in ethylene glycol and various ionic liquids under microwave heating. The products were characterized by powder X-ray diffraction, electron microscopy, and upconversion (UC) luminescence spectroscopy. After Yb3+ excitation at 970 nm, Er3+ ions are excited by energy transfer upconversion and show the typical green and red emission bands. The UC luminescence intensity was optimized with respect to reactant concentrations, solvents, and reaction temperature and time. The strongest UC emission was achieved for sub-20 nm core-shell nanoparticles which were obtained in the ionic liquid diallyldimethylammonium bis(trifluoromethanesulfonyl)amide from a two-step synthesis without intermediate separation. Strictly anhydrous reaction conditions, a high fluoride/rare earth ion ratio, and a core-shell structure are important parameters to obtain highly luminescent nanoparticles. These conditions reduce non-radiative losses due to defects and high energy acceptor modes of surface ligands. A low power excitation of the core-shell particles by 70 mW at 970 nm results in an impressive UC emission intensity of 0.12% compared to the bulk sample.
- Tessitore, Gabriella,Mudring, Anja-Verena,Kr?mer, Karl W.
-
p. 34784 - 34792
(2019/11/14)
-
- Magnetism and optical properties of Yb3Al5O12 hosted Er3+ – experiment and theory
-
Using the recently developed method based on a combination of DFT plane wave code applied to extract the crystal field parameters and a local atomic like Hamiltonian involving electron-electron, spin-orbit and Zeeman terms we calculated the energy levels of ground and excited multiplets of Yb3+ and Er3+ ions hosted in ytterbium and yttrium aluminum garnet (YbAG and YAG) including their crystal and magnetic field splitting. The obtained energy levels and derived magnetic properties are compared with the experimental data from magnetometry, photoluminiscence and near-infrared spectroscopy.
- Sedmidubsky, David,Jake?, Vít,Rube?ová, Kate?ina,Nekvindová, Pavla,Hlásek, Tomá?,Yatskiv, Roman,Novák, Pavel
-
-
- NaYF4:Yb,Er/NaYF4 Core/Shell Nanocrystals with High Upconversion Luminescence Quantum Yield
-
Upconversion core/shell nanocrystals with different mean sizes ranging from 15 to 45 nm were prepared via a modified synthesis procedure based on anhydrous rare-earth acetates. All particles consist of a core of NaYF4:Yb,Er, doped with 18 % Yb3+ and 2 % Er3+, and an inert shell of NaYF4, with the shell thickness being equal to the radius of the core particle. Absolute measurements of the photoluminescence quantum yield at a series of different excitation power densities show that the quantum yield of 45 nm core/shell particles is already very close to the quantum yield of microcrystalline upconversion phosphor powder. Smaller core/shell particles prepared by the same method show only a moderate decrease in quantum yield. The quantum yield of 15 nm core/shell particles, for instance, is reduced by a factor of three compared to the bulk upconversion phosphor at high power densities (100 W cm?2) and by approximately a factor of 10 at low power densities (1 W cm?2).
- Homann, Christian,Krukewitt, Lisa,Frenzel, Florian,Grauel, Bettina,Würth, Christian,Resch-Genger, Ute,Haase, Markus
-
supporting information
p. 8765 - 8769
(2018/07/14)
-
- Novel and easy access to highly luminescent Eu and Tb doped ultra-small CaF2, SrF2 and BaF2 nanoparticles-structure and luminescence
-
A universal fast and easy access at room temperature to transparent sols of nanoscopic Eu3+ and Tb3+ doped CaF2, SrF2 and BaF2 particles via the fluorolytic sol-gel synthesis route is presented. Monodisperse quasi-spherical nanoparticles with sizes of 3-20 nm are obtained with up to 40% rare earth doping showing red or green luminescence. In the beginning luminescence quenching effects are only observed for the highest content, which demonstrates the unique and outstanding properties of these materials. From CaF2:Eu10 via SrF2:Eu10 to BaF2:Eu10 a steady increase of the luminescence intensity and lifetime occurs by a factor of ≈2; the photoluminescence quantum yield increases by 29 to 35% due to the lower phonon energy of the matrix. The fast formation process of the particles within fractions of seconds is clearly visualized by exploiting appropriate luminescence processes during the synthesis. Multiply doped particles are also available by this method. Fine tuning of the luminescence properties is achieved by variation of the Ca-to-Sr ratio. Co-doping with Ce3+ and Tb3+ results in a huge increase (>50 times) of the green luminescence intensity due to energy transfer Ce3+ → Tb3+. In this case, the luminescence intensity is higher for CaF2 than for SrF2, due to a lower spatial distance of the rare earth ions.
- Ritter, Benjamin,Haida, Philipp,Fink, Friedrich,Krahl, Thoralf,Gawlitza, Kornelia,Rurack, Knut,Scholz, Gudrun,Kemnitz, Erhard
-
p. 2925 - 2936
(2017/03/11)
-
- Core-shell metal fluoride nanoparticles: Via fluorolytic sol-gel synthesis-a fast and efficient construction kit
-
An efficient, fast and easy construction kit using the fluorolytic sol-gel synthesis of rare-earth-doped alkaline earth fluoride core-shell nanoparticles at room temperature is presented, capable of synthesizing several hundred grams to kilograms of core-shell particles in one batch. We show ways for an effective design of energy transfer core-shell systems. Undoped metal fluoride shells rigorously shield a luminescent core from the surrounding solvent, resulting in higher quantum yields, longer lifetimes of the excited states, and finally a brighter luminescence. The heavy SrF2 shields a luminescent core from the surrounding solvent three times more effectively than the light CaF2. Energy transfer processes from core to shell are more efficient than vice versa, and hence, absorbing cores are more effective than absorbing shells. The application of these materials in the preparation of transparent tunable luminescent materials showing different luminescence colours upon different excitation wavelengths is demonstrated.
- Ritter,Haida,Krahl,Scholz,Kemnitz
-
p. 5444 - 5450
(2017/07/10)
-
- Syntheses, structures and photophysical properties of heterotrinuclear Zn2Ln clusters (Ln = Nd, Eu, Tb, Er, Yb)
-
Heterotrinuclear Zn2Ln (Ln = Nd 2, Eu 3, Tb 4, Er 5, Yb 6) clusters [(Znq2)2](μ-CH3COO){Ln(hfac) 2} (q = 8-hydroxylquinolinate, hfac = hexafluoroacetylacetonate) have been synthesized. The Zn2Ln framework is ligated by two q ligands featuring μ-phenoxo and two q ligands featuring μ3-phenoxo coordination modes, and one μ-CH3COO- anions. Since the short intramolecular separations of Zn...Ln (ca. 3.354-3.373 A) allow energy transfer from Znq2-based sensitizers to the Ln III centres through two energy transfer pathways, the lanthanide luminescence is indeed lighted up by excitation of the Znq 2-based chromopores. Photophysical measurements revealed that these Zn2Ln complexes exhibit the so-called dual emission originating from both Znq2-based luminophores and lanthanide emitters. By virtue of the dual luminescence with complementary colours, the Znq2-based cyan emission and EuIII-centred red luminescence are combined to generate a white-light emission in the Zn 2Eu (3) complex.
- Xu, Hai-Bing,Zhong, Ye-Teng,Zhang, Wei-Xiong,Chen, Zhong-Ning,Chen, Xiao-Ming
-
p. 5676 - 5682
(2010/09/17)
-