Enhancement of the sensitivity of single band ratiometric luminescent nanothermometers based on Tb3+ ions through activation of the cross relaxation process

Joanna Drabik,Lukasz Marciniak,Robert Kowalski

doi:10.1038/s41598-020-68145-5

Joanna Drabik, Lukasz Marciniak + Show 1 more

Open Access

https://doi.org/10.1038/s41598-020-68145-5

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Abstract

The description of luminescent processes and their thermally induced changes, that may be also influenced by the optically active ions concentration, and thus by the various inter-ionic processes, is the key to the improved development of luminescence thermometry. A phosphor doped with only trivalent terbium ions was described, which, by using two excitation lines fitted to the 7F6 → 5D3 and 7F5 → 5D3 transitions, shows a luminescent signals with the opposite characteristics of intensity changes as a function of temperature. By modifying the concentration of Tb3+ ions, the probability of {5D3, 7F6} ↔ {5D4, 7F0} cross-relaxation was being altered, which turned out to have a beneficial effect on the properties of the described nanothermometers. The ratio of intensities for both excitations was found to be temperature dependent, which resulted in high relative sensitivities of temperature readout reaching 3.2%/°C for 190 °C and not reaching values below 2%/°C in the broad range of the temperature. Extensive decay time measurements for 5D3 and 5D4 emissive levels were presented and the variability of both rise- and decay times as a function of terbium concentration and temperature was investigated. Thanks to this, conclusions were drawn regarding thermally dependent optical processes occurring in a given and similar systems.

Highlights

The description of luminescent processes and their thermally induced changes, that may be influenced by the optically active ions concentration, and by the various inter-ionic processes, is the key to the improved development of luminescence thermometry
The technique of high-resolution noncontact temperature measurement in the single-band-ratiometric (SBR) approach has been recently developed[1,2,3,4,5,6]. It is an application of luminescence thermometry technique[7,8,9,10] which requires only one type of optically active center in any nanocrystalline matrix, and enables temperature readout with high resolution and significant relative sensitivity ( Sr)
The phosphors used in this approach may be based on different luminescent dyes or ions, whose emission intensity depends on the temperature in opposite ways, depending on the excitation line used

Summary

Introduction

The description of luminescent processes and their thermally induced changes, that may be influenced by the optically active ions concentration, and by the various inter-ionic processes, is the key to the improved development of luminescence thermometry. The technique of high-resolution noncontact temperature measurement in the single-band-ratiometric (SBR) approach has been recently developed[1,2,3,4,5,6] It is an application of luminescence thermometry technique[7,8,9,10] which requires only one type of optically active center in any nanocrystalline matrix, and enables temperature readout with high resolution and significant relative sensitivity ( Sr). A different selection of the excitation wavelengths presented in this work facilitates the concentration quenching of the luminescence related to the T b3+ content-activated cross-relaxation (CR) process This is a much more universal description that covers all possible luminescent processes both intraand inter-ionic, in systems based on any lanthanide in general, but above all a way to enhance the Sr values in a wide temperature range. In order to understand the impact of all the processes occurring in the studied system, an experimental and theoretical analysis of the change in their probabilities depending on temperature was carried out

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