Optical fibre thermometry using ratiometric green emission of an upconverting nanoparticle-polydimethylsiloxane composite

Abstract

The thermally coupled green band emission from excited Er 3+ ions has been used in the past to create optical thermometers, by doping the material in various types of media, particularly glasses.Glasses are known to be excellent hosts for Er 3+ ions: however, high temperatures (>900 K) are usually required for doping these ions into glasses and a non-linear temperature response is often produced. In this work, the frequently encountered drawbacks of glass-based temperature sensors have been addressed by developing a temperature sensor created at a lower temperature (543 K), by dip-coating chemically synthesized upconverting nanoparticles (UCNP -NaYF4:(18%) Yb 3+ , (2%) Er 3+ ) embedded in polydimethylsiloxane (PDMS) onto the tip of a 1000 μm optical fibre, to create the actual fibre probe. The sensor shows an excellent linear response (R 2 = 0.991) over a very useful temperature range of 295 K -473 K, with a sensitivity of 2.9 ×10 -3 K -1 , a temperature resolution of ± 2.7 K and response time of ~ 5 seconds. Additionally, a probe was investigated where a pure upconverting nanoparticle powder was coated on the tip of optical fibre and its spectral and temperature response was obtained (and cross compared with that of UCNP-PDMS composite). The results obtained from the probe development work show that the UCNP-PDMScoated optical fibre temperature sensor developed offers a better alternative to more conventional Er 3+ doped glass-based temperature sensors, in terms of the thermal budget, the synthesis process and the ease of coating, creating as a result, a very linear device response.

Water‐Stable and Photo‐Patternable Siloxane‐Encapsulated Upconversion Nanoparticles toward Flexible Near‐Infrared Phototransistors

“…[42] The upconversion PL decay lifetime for green emission at 520 nm (Figure 2b) shortened from 328.78 to 313.68 µs after water soaking for 2 h. The green-to-red upconversion emission ratio (G/R) and the decay lifetime of UCNP@SiOx bulk were affected only slightly by water immersion (Figure 2c). The G/R values decreased slightly from 2.61 to 2.52 after soaking for 2 h. To compare the water-stability of UCNP@SiOx with UCNP embedded in polydimethylsiloxane (UCNP-PDMS), we measured the PL spectra of UCNP-PDMS during soaking in water for 2 h. PDMS is a commonly used silicone encapsulation for various fluorescent materials, such as an organic light emitting diode, [43] perovskite, [44] quantum dot, [45] and UCNP, [46][47][48] due to its autofluorescence, high elasticity, optical transparency, and biocompatibility. [49,50] The G/R values of OA-UCNP and UCNP-PDMS were 2.79 and 2.78, respectively, indicating no degradation of photoluminescence after the polymerization process of PDMS (Figure S3a,c, Supporting Information).…”

Recent advances in lanthanide-doped up-conversion probes for theranostics

“…The pure Ln-UCNPs and Ln-UCNPs-PDMS composite materials were coated on optical fibers for temperature sensing. The sensor coated with composite material displayed a linear response from 295 to 473 K ( Kumar et al, 2020 ). A recent report demonstrated the coating of a temperature-dependent Ln-UCNPs onto the surface of spider silk, a natural optical fiber, to construct a temperature sensor with good biocompatibility.…”

Preparation and Applications of Polydimethylsiloxane‐Based Fluorescent Materials

“…Kumar et al fabricated upconverting nanoparticles (UCNP-NaYF 4 :(18%) Yb 3+ , (2%) Er 3+ ) and blended them with PDMS, then coated them on the optical fiber tip by dipping method to obtain linear temperature sensor. [82] Zhang et al synthesized crown functionalized TPE macrocycle molecule and mixed it into PDMS to obtain a detection strip that can recognize benzene, which is shown as color transition from blue to yellow-green. [83] In previous studies, detecting pesticide residues by using conventional QDs through fluorescence quenching has emerged endlessly.…”