Abstract
A new type of polymer, based on the oxadiazole group, has been tested as indicator material for a ratiometric photoluminescence and optical reflection based temperature sensor in the temperature range between 30°C and 60°C. Thin films of the new polymer have been deposited by spin-coating on a glass substrate, excited by means of a low-cost near UV-LED. The optical spectrum, as detected by a fiber-based PC-card optical spectrometer, consisted of the reflection peak at the excitation wavelength and two distinct photoluminescence peaks at 430 nm and 480 nm, both in the blue spectral region. The peak amplitudes of all three spectral peaks depend linearly on the exciting light intensity. Changing the sample temperature, all peak amplitude values decrease monotonously with increasing temperature. By using a ratiometric approach, it has been found that the ratio between the two photoluminescence peaks was almost constant with temperature, while the ratio between the main photoluminescence peak at 430 nm and the reflection peak around 380 nm scaled nicely with the ambient temperature. Therefore, it has been proposed to use the latter criterion and a simple polynomial fit to the temperature versus peak amplitude relation.
Highlights
Temperature sensing is one of the most classical sensor domains
By using a ratiometric approach, it has been found that the ratio between the two photoluminescence peaks was almost constant with temperature, while the ratio between the main photoluminescence peak at 430nm and the reflection peak around 380 nm scaled nicely with the ambient temperature
The film thickness has been determined by atomic force microscope (AFM) imaging of the films, deposited on the glass substrate and cut with a razor blade
Summary
Temperature sensing is one of the most classical sensor domains. Despite the availability of excellent integrated silicon solutions with good linearity and sensitivity over a large temperature range there is even in this field a lot of research going on [1,2,3]. Optical temperature sensors, based on band-edge shifts, enable the easy realization of optical fiber-based solutions that permit measuring the temperature in remote location [12] Another important research field, where conventional sensors are difficult to use, is biology. X 1− a in vivo measurements have, for example, been achieved by using a dual emissive phosphorescent polymeric thermometer that incorporates two long-lived phosphorescent iridium complexes into an acrylamide-based thermosensitive polymer [13] In this case, even intracellular temperature measurements have been reported. In literature [13] it is, for example, reported that, for some materials with multiple peak emission, the ratio between different emission peak amplitudes is a good measure for the sample temperature This is checked in the case of the proposed oxadiazole based polymer and compared to different ratiometric criteria
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