Issue 30, 2018

Thermoplasmonic enhancement of upconversion in small-size doped NaGd(Y)F4 nanoparticles coupled to gold nanostars

Abstract

Plasmon enhancement of luminescence is a common strategy to boost the efficiency of both fluorescence and upconversion via the augmented local electromagnetic field. However, the local heating produced when exciting the plasmon resonance of metallic nanoparticles is often overlooked. As higher temperatures are usually detrimental for radiative processes, only the electromagnetic contribution is exploited for enhancement. We show here that for small size (<20 nm) rare-earth doped β-NaGd(Y)F4 upconversion nanoparticles (UCNPs), the photothermal properties of gold nanostars (AuNSs) can be used to enhance the total emission intensity. On the contrary, for UCNPs of larger size, the thermoplasmonic effect is adverse for the emissivity. Therefore, we developed a novel strategy to enhance the emission intensity by combining the thermoplasmonic effect on AuNSs with the size-dependent thermal properties of UCNPs. Furthermore, by following the integrated intensity ratio between the emission lines of Er3+, 2H11/24I15/2 and 4S3/24I15/2, a direct correlation between the local temperature and the emission intensity could be established. Optical thermometry measurements show that the thermoplasmonic effect in AuNSs, with a plasmon absorption band close to the excitation wavelength, can produce an increment of the local temperature of more than 100 °C when exposed to 976 nm continuous-wave laser light at 50 W cm−2 of power density. The results provided here are relevant for the design and implementation of plasmon-enhanced luminescent devices, upconversion solar-cells, bioprobes and also for hyperthermia.

Graphical abstract: Thermoplasmonic enhancement of upconversion in small-size doped NaGd(Y)F4 nanoparticles coupled to gold nanostars

Supplementary files

Article information

Article type
Paper
Submitted
26 feb 2018
Accepted
11 jul 2018
First published
12 jul 2018

Nanoscale, 2018,10, 14687-14696

Thermoplasmonic enhancement of upconversion in small-size doped NaGd(Y)F4 nanoparticles coupled to gold nanostars

E. D. Martínez, R. R. Urbano and C. Rettori, Nanoscale, 2018, 10, 14687 DOI: 10.1039/C8NR01639A

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