Abstract
A new thermographic nanocrystalline Sr4Al14O25:Mn4+,Tb3+ phosphor was developed, and the concentrations of both dopants and the synthesis conditions were optimized. The combination of the thermally quenched luminescence from the Mn4+ ions to the almost temperature-independent emission from Tb3+ provides a sensitive luminescent thermometer (SR = 2.8%/°C at 150 °C) with strong emission color variability. In addition, a figure of merit for this luminescence thermochromism was proposed, as the relative sensitivities of the x and y CIE coordinates, which for this phosphor reaches at 150 °C SR(x) = 0.6%/°C and SR(y) = 0.4%/°C, respectively. Noncontact thermal imaging was demonstrated with this phosphor using a single consumer digital camera and exploiting the ratio of red (R) and green (G) channels of the RGB images, thereby confirming the high application potential of Sr4Al14O25:Mn4+,Tb3+ nanocrystals for thermal sensing and mapping.
Highlights
IntroductionLuminescence thermometry (LT) is a class of optical techniques exploiting the temperature dependence of luminescence processes of tracers introduced in transparent fluids or solids or coated onto surfaces to measure their temperature remotely.[1−6] By allowing spatial, temporal, and spectral discrimination in both laser excitation and luminescence detection processes, luminescence thermometry allows remote sensing with high spatial and temporal resolution and can be applied in environments with high luminosity, which are significant advantages against intrusive probes and infrared thermography.[7−10] These lends LT a large application potential, in particular for nanothermometry, for example, on microelectronics,[11] lab-on-a-chip systems,[12] and in biomedicine;[9,13] for the study of rapidly varying phenomena, for example, in fluid flows[14] or on rotating parts;[15] and for robust thermometry in harsh environments with significant luminosity, for example, on burning materials[16] or in internal combustion engines.[16]
Lanthanide (Ln)-doped thermographic phosphors are some of the most commonly used materials for this type of applications. It is well-known that for f−f electronic transitions occurring in Ln3+ ions, multiphonon relaxation is usually responsible for thermal quenching of the whole luminescence emission, which occurs only at elevated temperature
This has the advantage of a detectable emission over wide temperature ranges, with measurements reported up to 1400 K,18 but it results in the limited temperature sensitivity of this response around ambient temperature when the goal is to detect smaller temperature variations
Summary
Luminescence thermometry (LT) is a class of optical techniques exploiting the temperature dependence of luminescence processes of tracers introduced in transparent fluids or solids or coated onto surfaces to measure their temperature remotely.[1−6] By allowing spatial, temporal, and spectral discrimination in both laser excitation and luminescence detection processes, luminescence thermometry allows remote sensing with high spatial and temporal resolution and can be applied in environments with high luminosity, which are significant advantages against intrusive probes and infrared thermography.[7−10] These lends LT a large application potential, in particular for nanothermometry, for example, on microelectronics,[11] lab-on-a-chip systems,[12] and in biomedicine;[9,13] for the study of rapidly varying phenomena, for example, in fluid flows[14] or on rotating parts;[15] and for robust thermometry in harsh environments with significant luminosity, for example, on burning materials[16] or in internal combustion engines.[16]. Lanthanide (Ln)-doped thermographic phosphors are some of the most commonly used materials for this type of applications It is well-known that for f−f electronic transitions occurring in Ln3+ ions, multiphonon relaxation is usually responsible for thermal quenching of the whole luminescence emission, which occurs only at elevated temperature. This has the advantage of a detectable emission over wide temperature ranges, with measurements reported up to 1400 K,18 but it results in the limited temperature sensitivity of this response around ambient temperature when the goal is to detect smaller temperature variations. The decrease in the luminescence lifetime as a result of this quenching is Received: June 28, 2020 Accepted: September 9, 2020 Published: September 9, 2020
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