Instantaneous ballistic velocity of suspended Brownian nanocrystals measured by upconversion nanothermometry

Abstract

Brownian motion is one of the most fascinating phenomena in nature. Its conceptual implications have a profound impact in almost every field of science and even economics, from dissipative processes in thermodynamic systems, gene therapy in biomedical research, artificial motors and galaxy formation to the behaviour of stock prices. However, despite extensive experimental investigations, the basic microscopic knowledge of prototypical systems such as colloidal particles in a fluid is still far from being complete. This is particularly the case for the measurement of the particles' instantaneous velocities, elusive due to the rapid random movements on extremely short timescales. Here, we report the measurement of the instantaneous ballistic velocity of Brownian nanocrystals suspended in both aqueous and organic solvents. To achieve this, we develop a technique based on upconversion nanothermometry. We find that the population of excited electronic states in NaYF:Yb/Er nanocrystals at thermal equilibrium can be used for temperature mapping of the nanofluid with great thermal sensitivity (1.15% K at 296 K) and a high spatial resolution (<1 μm). A distinct correlation between the heat flux in the nanofluid and the temporal evolution of Er emission allows us to measure the instantaneous velocity of nanocrystals with different sizes and shapes.

Physical Manipulation of Lanthanide‐Activated Photoluminescence

“…Nonradiative transition dissipates the energy of the excited state by means of crystal lattice vibration, that is, the phonon. [57][58][59] Similar ratio regulation could also be acquired in Yb 3+ /Tm 3+ ( 1 G 4 → 3 H 5 to 3 H 4 → 3 H 6 of Tm 3+ ) and Yb 3+ /Er 3+ ( 4 D 7/2 → 4 I 15/2 to 2 I 11/2 → 4 I 15/2 of Er 3+ ) co-doped nanocrystals. As a common example, thermal deactivation of the 5 D 0 electronic state of Eu 3+ ion reduces luminescence intensity as temperature increases.…”

High Phase‐Purity 1T‐MoS2 Ultrathin Nanosheets by a Spatially Confined Template

“…The obtained ultrathin nanosheets exhibit good electrocatalytic activity and excellent stability in the hydrogen evolution reaction.Nanomaterials have shown various promising applications in optics, [1] catalysis, [2] and electronics, [3] owing to their unique physiochemical properties,w hich strongly depend on the crystal facet, morphology,d imension, and size.I nr ecent years,t he crystal phase has been reported as an important factor to affect the physical-chemical properties.F or exam-ple,M oS 2 is at ypical polyphase material which includes trigonal (1T), hexagonal (2H), rhombohedral (3R), and 1T' forms. Moreover,b oth the confined space and the structure of template will affect the purity of 1T-MoS 2 ;i nt his case,t his approach was extended to other similar spatially confined templates to obtain the high-purity material.…”

“…Nanomaterials have shown various promising applications in optics, [1] catalysis, [2] and electronics, [3] owing to their unique physiochemical properties,w hich strongly depend on the crystal facet, morphology,d imension, and size.I nr ecent years,t he crystal phase has been reported as an important factor to affect the physical-chemical properties.F or exam-ple,M oS 2 is at ypical polyphase material which includes trigonal (1T), hexagonal (2H), rhombohedral (3R), and 1T' forms. [4] Among them, the unique structure of 1T phase MoS 2 endows it with am etallic-like property, [5] showing higher electrical conductivity and catalytic activity.…”

Confining Excitation Energy in Er3+‐Sensitized Upconversion Nanocrystals through Tm3+‐Mediated Transient Energy Trapping

“…[12] Xray powder diffraction studies revealed the hexagonal phase of the as-prepared samples (see Figure S1 in the Supporting Information). [12] Xray powder diffraction studies revealed the hexagonal phase of the as-prepared samples (see Figure S1 in the Supporting Information).…”