Abstract
Oxygen-free Eu(3+)-doped NaGdF4 nanocrystals with high quantum cutting efficiency are accessible at low temperatures (room temperature to 80 °C) using task-specific ionic liquids (ILs) as structure directing agents and only water as solvent. Selective tuning of the shape, morphology and, most importantly, the crystal phase of the host lattice is achieved by changing the alkyl side length, the H-bonding capabilities and the concentration of 1-alkyl-3-methylimidazolium bromide ILs, [C(n)mim]Br. When using [C2mim]Br, hexagonal NaGdF4 nanoparticles are obtained. In the case of methylimidazolium bromides with longer pendant alkyl chains such as butyl (C4), octyl (C8) or decyl (C10), extremely small nanoparticles of the cubic polymorph form, which then convert even at room temperature (RT) to the thermodynamically favored hexagonal modification. To the best of our knowledge, this kind of spontaneous phase transition is not yet reported. The hexagonal nanomaterial shows a substantial quantum cutting efficiency (154%) whilst in the cubic material, the effect is negligible (107%). The easy yet highly phase selective green synthesis of the materials promises large scale industrial application in environmentally benign energy efficient lighting.
Highlights
There is growing societal demand for producing energy efficient lighting and developed countries have started to ban classic incandescent lamps
To understand the effect of hydrogen bonding, 1-ethyl-dimethylimidazolium bromide [C2dmim]Br, in which C(2)–H is replaced by methyl, is used in a similar synthesis
We have succeeded in preparing efficient quantum cutting NaGdF4:Eu nanocrystals useful for energy efficient lighting, using ionic liquids (ILs) as nanosynthetic templates at room temperature
Summary
Achieved by a two-photon down-conversion process based on a combination of two different rare earth ions, i.e. Gd3+ and Eu3+ in NaGdF4:Eu3+, where the excitation energy is transferred via a two-step process from the quantum cutter (Gd3+) to the emitting ion (Eu3+), resulting in the emission of two visible photons.[1,3] ternary lanthanide fluorides like NaGdF4 are amongst the most effective optical materials and they are used widely in photonics and biophotonics, because of their high refractive index, low phonon energy and good stability.[3,4,5,6]. We present an easy yet highly phase selective synthesis of oxygen-free Eu3+-doped NaGdF4 nanocrystals ( particle size below 10 nm) with high quantum cutting efficiency. The synthesis only requires stirring an aqueous solution of the starting materials and a task-specific IL such as [C2mim]Br (1-ethyl-3-methylimidazolium bromide) for one hour at room temperature. This synthesis protocol meets with the requirements of green chemistry as proposed by Anastas and Warner[58] and offers the possibility of easy scale-up for industrial manufacturing. Phase transition of nanomaterials needs at least one of the following changes: heating at high calcination temperatures, change of the reactant ratio and other external influences etc.[59,60,61,62] But in the present case, spontaneous phase transition over time without using any external force is new and novel for sodium ternary fluoride and very rare for other systems
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
