Enabling Nonthermally Coupled Upconversion in a Core–Shell–Shell Nanoparticle for Ultrasensitive Nanothermometry and Anticounterfeiting

Luminescence intensity ratio (LIR)-based thermometry has the advantages of high relative sensitivity, fast temperature response, and high spatial resolution. However, the current LIR-based systems are mainly based on thermally coupled energy levels, which have low sensitivity due to the intrinsic limitation of the Boltzmann distribution theory. Here, we report a design of a core–shell–shell nanostructure to improve the thermal sensitivity by using the nonthermally coupled upconversion emissions. Ho3+ and Tm3+ were selected as emitters and spatially separated by an inert interlayer. The upconverted Tm3+ emissions show a dramatical thermal enhancement while the Ho3+ emissions show a decline with increasing temperature, resulting in a huge LIR (695 nm/645 nm) contrast and thereafter a high relative sensitivity (9.78% K–1 at room temperature). In addition, this nanostructure design presents a color change from red to blue at different excitation powers and also from red to green by tuning the excitation laser pulse widths. These results hold great potential in the field of noncontact ultrasensitive temperature sensors and multimodel anticounterfeiting

Amplifying Photon Upconversion in Alloyed Nanoparticles for a Near-Infrared Photodetector

Photon upconverison has attracted a substantial amount of interest in diverse fields due to its characteristic anti-Stokes emissions. However, obtaining intense emission under low-power laser irradiation has remained a challenge. Here we report a mechanistic design of activator–sensitizer alloyed nanoparticles to achieve bright upconversion under weak infrared irradiation. This design allows a nearest sensitizer–activator separation to facilitate efficient energy transfer that results in remarkably enhanced upconversion (>2 orders of magnitude) under 0.26 W cm–2 irradiation compared to that of the Er sublattice, and the upconversion quantum yield also shows a 20-fold increase. Interestingly, the alloyed nanoparticles exhibit a gradual change in emission color with an increase in Yb3+ content, and moreover, their emission colors can be dynamically controlled by simply modulating the excitation laser power and pulse widths. Such alloyed nanoparticles show great promise for application in a near-infrared photodetector