Synthesis of Core–Shell ScF₃ Nanoparticles for Thermal Enhancement of Upconversion

Abstract

Lanthanide-doped ScF3 nanoparticles are synthesized and explored for thermal enhancement of upconversion. A hot-injection method is developed to control the formation of ScF3 nanoparticles with a core–shell nanostructure of uniform size and morphology. Temperature dependence of the upconversion emission is investigated in the temperature range from 168 to 308 K. In contrast to typical NaYF4:Yb/Er@NaYF4 nanoparticles that display thermally quenched emissions, a 3.7-fold enhancement of the upconversion emission is recorded for the ScF3:Yb/Er@ScF3 nanoparticles as the temperature is increased from 168 to 248 K because of the negative thermal expansion of the ScF3 host lattice. Besides, the emission profiles of the nanocrystals also display a strong temperature dependence, enabling convenient ratiometric thermometry with a relative sensitivity of 1.73%·K–1 at 168 K. As the core–shell nanoparticles are minimally susceptible to surface quenching, our findings may inspire new ideas for developing thermally enhanced upconversion nanoparticles with high emission intensities.

Thermal enhancement of upconversion in lanthanide-doped Gd2Ti2O7 crystals via fast evaporation in a sol–gel procedure

“…For instance, the negative thermal quenching effect was reported in the ytterbium (Yb 3+ ) sensitized upconversion (UC) nanocrystals (NCs), which was attributed to the enhanced energy transfer efficiency from Yb 3+ sensitizers to activators (Er 3+ , Ho 3+ or Tm 3+ ) upon increasing the temperature. 29–32 The major limitation of these UCNCs is the irreversibility after heating over 433 K. Upon using the matrix of Yb 2 WO 12 or Sc 2 Mo 3 O 12 prepared via a high temperature solid-state reaction method, the phenomenon of the thermal enhancement of UC is achieved owing to the negative lattice expansion promoted energy transfer efficiency, which is reversible in the range of 303–573 K. 33,34 However, these products belong to micron-sized bulk materials, and it remains a challenge to realize the fully reversible negative thermal quenching effect over a broad temperature range in lanthanide doped UC systems with submicron sizes.…”

Controlling upconversion in emerging multilayer core–shell nanostructures: from fundamentals to frontier applications

“…227 These designs with different or even contrary changes in emission intensities are capable of realizing ultrasensitive thermometry towards various temperature measurement scenarios. [228][229][230][231] On the other hand, this research may also benefit from other effective optical designs. A combination of two kinds of upconversion processes, namely the regular upconversion luminescence and second harmonic generation, can be also used for ultrasensitive temperature sensing.…”

Recent Advances in All‐Inorganic Zero‐Dimensional Metal Halides

“…The rapid injection induces a sudden supersaturation of monomers, a short burst of nucleation, and subsequent crystal growth. The hot injection is popular for the synthesis of a series of nanocrystals such as chalcogenide semiconductor quantum dots, rare earth fluoride upconversion nanocrystals, and metal halide nanocrystals [32–34] . In a representative example, Manna and co‐workers reported the synthesis of 0D Cs 4 PbBr 6 nanocrystals through a hot injection method [35] .…”