Mit einer Quantenausbeute von 70 % grün lumineszierende CePO₄:Tb‐Nanopartikel mit einer Schale aus LaPO₄

Abstract

Lumineszente Nanokristalle können als aktive Komponenten in Bildschirmen, [1a] Lasern mit niedriger Schwellenenergie [1b] und optischen Verstärkern [1c] sowie als Marker für Biomoleküle [1d] dienen, sofern ihre Photolumineszenz-Quantenausbeute hoch ist. In den letzten Jahren wurden deshalb Strategien entwickelt, um Energieverlustprozesse an der Partikeloberfläche zu verringern und so die Quantenausbeute von Nanopartikeln deutlich zu erhöhen. Im Fall der Halbleiter-Nanopartikel konnte dies erreicht werden, indem man um jeden Nanokristall eine kristalline Schale aus einem geeigneten Material mit großer Energielücke epitaktisch aufwachsen ließ.[

Ionic Liquid Based Approach to Luminescent LaPO4:Ce,Tb Nanocrystals: Synthesis, Characterization and Application

“…[8] These values are even more surprising since neither strongly coordinating solvents or stabilizers nor advanced core-shell structures are applied to protect the surfaces of the nanoparticles. [7] Previous studies have already shown the IL constituents to be adhered on the surface of the nanocrystals via charge interaction. Due to the "non"-coordinating properties of the IL, its constituents can be removed completely just by washing with ethanol that is saturated with NaCl.…”

“…[6] When also introduc- ing LaPO 4 @LaPO 4 :Ce,Tb core-shell structures, quantum yields of 70 % (Tb 3+ emission) and 80 % (Ce 3+ /Tb 3+ emission) have been gained. [7] However, the removal of surfaceactive solvents/stabilizers subsequent to synthesis as well as the application of advanced core-shell structures lead to a process that becomes more and more complicated, timeconsuming, and expensive.…”

Upconverting Nanoparticles

“…The Er 3+ ‐doped LuPO 4 and YbPO 4 nanoparticles were prepared by coprecipitation in a method analogous to that used to prepare LaPO 4 :Ce 3+ ,Tb 3+ and CePO 4 :Tb 3+ nanocrystals 335. 336 Bulk LaPO 4 :Ce 3+ ,Tb 3+ is a commercially applied lamp phosphor 337. 338 Redispersible Er 3+ ‐doped YVO 4 nanocrystals were synthesized in a hydrothermal process by Kong and co‐workers 84.…”

“…If the excitation energy is mainly transferred to the particle surface through neighboring dopant ions, the most straightforward choice for the shell material is the pure (i.e., undoped) host material of the core particle. The formation of core–shell particles with small lattice mismatch between the core and the shell material has been intensively investigated for semiconductor nanoparticles as well as for some doped nanomaterials with large bandgaps 336. 367, 417 More recently, synthesis procedures for core–shell particles of lanthanide fluoride material have been developed.…”

“…Ideally, a synchrotron radiation source is used, which allows tuning of the photon energy of the X‐rays exciting the sample. At low photon energies, only electrons of elements located in the outmost layers of the particle can reach the detector, whereas at high photon energies electrons from the core can also escape the particle, and the composition of the whole core–shell particle is probed 336. 427 Recently, van Veggel and co‐workers used this technique in combination with energy‐dispersive X‐ray spectroscopy (EDX) to demonstrate the existence of the core–shell structure of β‐NaYF 4 //β‐NaGdF 4 nanocrystals 420…”