Enhanced Luminescence, Collective Heating, and Nanothermometry in an Ensemble System Composed of Lanthanide‐Doped Upconverting Nanoparticles and Gold Nanorods

Abstract

A combined system of gold nanorods and NaGdF 4 :Er 3+ /Yb 3+ upconverting nanoparticles with double functionality, luminescence enhancement, and monitored heating is introduced. The paired nanostructures could become an excellent optical heater with thermal probe incorporated. To study their interaction, the longitudinal surface plasmon resonance of the gold nanorods is tuned to 980 nm, in resonance with the Yb 3+ absorption wavelength, so they can be simultaneously excited. Gold nanorods create a localized electromagnetic fi eld that enhances the emission intensity from upconverting nanoparticles. This luminescence enhancement is shown to depend on the interparticle distance and excitation power and, in this system, reaches a maximum enhancement of 9 for the green emission of Er 3+ ions. At the same time, evidence of strong collective heating from the gold nanorods is demonstrated. The temperature can be controlled by changing the excitation power and measured in situ via the Er 3+ thermally sensitive luminescence. At high excitation powers, the heating can trigger a deformation of the gold nanorods, which limits the maximum temperature achievable in the system to 160 °C. Combining these nanostructures provides an all-optical heating system with improved emission intensity that can monitor the temperature achieved.

Nanoplatforms for Plasmon‐Induced Heating and Thermometry

“…Hence, Au nanorods with 850 and 980 nm LSPR bands produce, respectively, a 49.7 and 77.9 % temperature increase over the 308 K measured for bare (Gd,Yb,Er) 2 O 3 nanorods (102 W cm −2 ). When compared with NRs‐AuNRs‐1.25, Au nanorods present a stronger heating effect due to the presence of longitudinal LSPR bands (Figure A–B), in accord with previous work . In particular, NaGdF 4 :Er 3+ /Yb 3+ upconverting nanoparticles mixed with Au nanorods reveal a 150 K increase in temperature when irradiated with a laser power density of 20 W cm −2 (corresponding to an increase of 7.5 K W −1 cm 2 ) .…”

“…Accordingly, the highest temperature increment was observed for NRs‐AuNRs‐980 nm‐C platforms (Figure B). However, these nanoplatforms have several limitations due to the resonance of the LSPR band with the excitation wavelength: (i) there is competition between LSPR and Yb 3+ absorption, reducing the Yb 3+ ‐to‐Er 3+ energy transfer efficiency and quenching Er 3+ emission; and (ii) the Er 3+ emission may be also quenched by Er 3+ ‐to‐Au energy transfer . Therefore, the optimal condition for Er 3+ 2 H 11/2 → 4 I 15/2 and 4 S 3/2 → 4 I 15/2 upconversion emission at the lowest possible laser power density (ca.…”

In vitro biomechanical properties, fluorescence imaging, surface-enhanced Raman spectroscopy, and photothermal therapy evaluation of luminescent functionalized CaMoO4:Eu@Au hybrid nanorods on human lung adenocarcinoma epithelial cells

“…lanthanide ion doped NPs or dye molecules) significantly enhances the luminescence efficiency or quenches their emission. [11,18] HNPs can be used for both in vivo fluorescence imaging and PTT.…”

Lanthanide upconversion luminescence at the nanoscale: fundamentals and optical properties

“…Recently, it was shown that the combination of gold nanorods and UCNPs deposited on thin films can function as a plasmon-enhanced nanothermometric structure 194 . Gold nanorods showed collective heating upon surface plasmon activation, which in turn tuned the green-to-red emission ratio of the UCNPs.…”