20981-49-1Relevant articles and documents
Novel and easy access to highly luminescent Eu and Tb doped ultra-small CaF2, SrF2 and BaF2 nanoparticles-structure and luminescence
Ritter, Benjamin,Haida, Philipp,Fink, Friedrich,Krahl, Thoralf,Gawlitza, Kornelia,Rurack, Knut,Scholz, Gudrun,Kemnitz, Erhard
, p. 2925 - 2936 (2017)
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.
Core-shell metal fluoride nanoparticles: Via fluorolytic sol-gel synthesis-a fast and efficient construction kit
Ritter,Haida,Krahl,Scholz,Kemnitz
, p. 5444 - 5450 (2017)
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.
Energy Migration Up-conversion of Tb3+ in Yb3+ and Nd3+ Codoped Active-Core/Active-Shell Colloidal Nanoparticles
Prorok, Katarzyna,Pawlyta, Miros?awa,Strek, Wies?aw,Bednarkiewicz, Artur
, p. 2295 - 2300 (2016)
The intentional design of chemical architecture of lanthanide doped luminescent nanoparticles through the proper selection of dopants in core-shell and core-shell-shell structures enables optimization of their optical properties. Such an approach allows one to achieve energy transfer up-conversion (ETU) and energy migration mediated up-conversion (EMU) and green emission from Tb3+ ions with the Yb3+ and Nd3+ sensitizers at 980 and 808 nm photoexcitation, respectively. The [Nd3+ → Yb3+]→ [Yb3+ → Tb3+] EMU phenomenon was significantly enhanced by spatial displacement of the sensitizing Nd3+ ions from the activator Tb3+ ions by intentionally introducing an intermediate Yb3+ sensitizer layer forming a [Nd3+ → Yb3+] → [Yb3+] → [Yb3+ → Tb3+] system. Otherwise Tb3+ emission was considerably quenched by Nd3+ ions even though they were spitted between the core and shell, respectively. Moreover, (Tb3+,Yb3+) → (Tb4+,Yb2+) valence change has been discovered to limit the Tb3+ up-conversion emission. The studies explain how the chemical architecture of the smartly designed active-core @ active-shell luminescent nanoparticles may improve their spectral properties.
Upconversion luminescence in sub-10 nm β-NaGdF4:Yb3+,Er3+ nanoparticles: An improved synthesis in anhydrous ionic liquids
Tessitore, Gabriella,Mudring, Anja-Verena,Kr?mer, Karl W.
, p. 34784 - 34792 (2019/11/14)
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.
