6. Optical temperature sensors

Optical temperature sensors represent an alternative to much more commonly used analytical tools such as resistance thermometers. Although for most applications temperature optodes might not be advantageous, in several areas they are of much interest. For instance, they can be used for ultrafast measurement of temperature in small volume which is difficult to realize with conventional tools. Temperature probes are also attractive for application in multi-parameter sensors since they allow for compensation of temperature effects on the optical sensors for other parameters without loss of spacious resolution. We prepared temperature optodes based on thermographic phosphors such as chromium(III)-activated yttrium aluminium borate [36] and based on polymer-immobilized metalorganic [37, 38] or purely organic dyes. [39] The last group of the dyes is particularly interesting since they are not only easily accessible synthetically and do not rely on use of precious metals but also deliver unmatched temperature coefficients in the decay time measurement (1.4-3.7 %/K at 25 °C). The potential of these probes is illustrated by Fig. 6.1. As one can see, a microsensor prepared on basis of one of these indicators immobilized into a gas-blocking polymer is exceptionally fast capable of recording the temperature changes in the sub-second time domain.
Figure 6.1. a) Schematic representation of the optical set-up of Firesting-mini phase fluorometer from Pyro Science. b) Photographic image of the phase fluorometer with the connected fiber-optic temperature sensor. c) Response of the sensor to temperature changes obtained by repeatable sensor transfer between two water-filled beakers (T = 22 and 37 °C, respectively).

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References:

[36] Borisov, S. M.; Gatterer, K.; Bitschnau, B.; Klimant, I. Preparation and Characterization of Chromium(III)-Activated Yttrium Aluminum Borate: A New Thermographic Phosphor for Optical Sensing and Imaging at Ambient Temperatures. The Journal of Physical Chemistry C 2010, 114 (19), 9118–9124. [37] Borisov, S.; Klimant, I. Blue LED Excitable Temperature Sensors Based on a New Europium(III) Chelate. JOURNAL OF FLUORESCENCE 2008, 18 (2), 581–589. [38] Borisov, S. M.; Klimant, I. New Luminescent Oxygen-Sensing and Temperature-Sensing Materials Based on Gadolinium(III) and Europium(III) Complexes Embedded in an Acridone–polystyrene Conjugate. Anal Bioanal Chem 2012, 404 (10), 2797–2806. [39] Steinegger, A.; Klimant, I.; Borisov, S. M. Purely Organic Dyes with Thermally Activated Delayed Fluorescence—A Versatile Class of Indicators for Optical Temperature Sensing. Advanced Optical Materials n/a-n/a.

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