Upconversion Nanocrystal Doped Polymer Fiber Thermometer

Abstract

In recent years, lanthanide-doped nanothermometers have been mainly used in thin films or dispersed in organic solvents. However, both approaches have disadvantages such as the short interaction lengths of the active material with the pump beam or complicated handling, which can directly affect the achievable temperature resolution. We investigated the usability of a polymer fiber doped with upconversion nanocrystals as a thermometer. The fiber was excited with a wavelength stabilized diode laser at a wavelength of 976 nm. Emission spectra were recorded in a temperature range from 10 to 35 ∘C and the thermal emission changes were measured. Additionally, the pump power was varied to study the effect of self-induced heating on the thermometer specifications. Our fiber sensor shows a maximal thermal sensitivity of 1.45%/K and the minimal thermal resolution is below 20 mK. These results demonstrate that polymer fibers doped with nanocrystals constitute an attractive alternative to conventional fluorescence thermometers, as they add a long pump interaction length while also being insensitive to strong electrical fields or inert to bio-chemical environments.

Influence of Pumping Regime on Temperature Resolution in Nanothermometry

“…The formalism used for this estimation can be found in [ 18 ]. Additional absorption, for example, by the host material, may further increase T but the measurement error caused by this can be easily calibrated as shown in [ 1 ].…”

“…One benefit of using varying lower energy levels is the spectral separation of the emission lines independent of the energy gap of the upper levels, therefore adding flexibility to measurements. Currently, the sensitivity of nanothermometers is characterized either under pulsed excitation [7,8] or continuous excitation [1,3]. This raises the question of whether calibration data acquired with either of these systems are interchangeable, even for the same active ion.…”

“…Luminescence based nanothermometry has established itself as a versatile approach to measuring temperature with high resolution in both thermal and spatial dimensions. The selling points of this technology are easily identified, as it is a non-contact measurement and it can be used for voluminous measurements in doped media [ 1 ] and on surfaces [ 2 ]. Moreover, it is robust against many external influences, such as electric fields [ 1 ].…”

“…The selling points of this technology are easily identified, as it is a non-contact measurement and it can be used for voluminous measurements in doped media [ 1 ] and on surfaces [ 2 ]. Moreover, it is robust against many external influences, such as electric fields [ 1 ]. The fundamental quantity to measure in nanothermometry is the luminescence intensity ratio (FIR) of two emission lines.…”

“…Currently, the sensitivity of nanothermometers is characterized either under pulsed excitation [ 7 , 8 ] or continuous excitation [ 1 , 3 ]. This raises the question of whether calibration data acquired with either of these systems are interchangeable, even for the same active ion.…”