Sensitivity Enhancement of the Tb³⁺-Based Single Band Ratiometric Luminescent Thermometry by the Metal-to-Metal Charge Transfer Process

Abstract

An improvement of the thermometric performance of a single band ratiometric luminescent thermometer by the boosting of its relative sensitivity can be executed either by an increase of the probability of the excited state absorption or by the enhancement of the luminescence thermal quenching upon ground state absorption. In this article, to achieve the latter, the metal-to-metal charge transfer process has been involved. To evaluate the utility of this approach, spectroscopic properties of the KGd(WO 4 ) 2 tungstate doped with different concentrations of Tb 3+ ions were investigated in a wide temperature range. It was found that the Tb 3+ luminescence was efficiently quenched at elevated temperatures because of the metal-to-metal charge transfer process despite the large energy gap between the emitting level 5 D 4 and the level below 7 F 0 (14800 cm −1 ). The probability of the metal-to-metal charge transfer process was found to be dependent on dopant amount, and the maximal relative sensitivity as high as 1.63%/°C was obtained for an optimal 80% of Tb 3+ concentration. The use of the metal-to-metal charge transfer phenomenon and the study of the influence of the dopant ion concentration on this process is an idea that can also significantly improve single band ratiometric nanothermometers based on other optically active ions.

Single‐Band Ratiometric Luminescent Thermometry Using Pr3+ Ions Emitting in Yellow and Red Spectral Ranges

“…[1][2][3][4][5][6][7] One of the new approaches in luminescent thermometry that has recently been given a particular attention is a single-band ratiometric (SBR), which exploits a single optically active center excited in two different ways, resulting in emission signals, the intensity of which have opposite temperature dependences. [8][9][10][11][12][13][14][15][16][17][18][19][20] The SBR luminescence thermometry has many advantages, including the fact that the emission is collected just in one chosen spectral range. This enables to avoid the detrimental effects of selective absorption of a tested medium, that may modify the shape of the emission spectrum, and thus the reliability of the temperature readout.…”

“…Up to date, SBR thermometry based on the emission of several ions has been demonstrated, with most of the work focusing on lanthanides (Tb 3þ , Eu 3þ , or Nd 3þ) . [8][9][10][11][12][15][16][17][18][19]21] Due to the well-defined and complex energy-level scheme, this type of ions can be successfully used to carry out a temperature reading in the SBR approach, using an excitations matched to the ground-(GSA) and the excited-state absorption (ESA). Most of the up-to-date reported SBR luminescent thermometers concern the near infrared (NIR) (Nd 3þ ) [18,19] or greenemitting phosphors (Tb 3þ ), [9,10,12,17,21] while only a few reports present luminescent thermometers operating in the red and yellow spectral ranges.…”

“…[ 8–12,15–19,21 ] Due to the well‐defined and complex energy‐level scheme, this type of ions can be successfully used to carry out a temperature reading in the SBR approach, using an excitations matched to the ground‐ (GSA) and the excited‐state absorption (ESA). Most of the up‐to‐date reported SBR luminescent thermometers concern the near infrared (NIR) (Nd 3+ ) [ 18,19 ] or green‐emitting phosphors (Tb 3+ ), [ 9,10,12,17,21 ] while only a few reports present luminescent thermometers operating in the red and yellow spectral ranges. Up to date only Eu 3+ ‐doped phosphors have been evaluated as SBR luminescent thermometers operating in those spectral ranges.…”

Dyes Encapsulated Nanoscale Metal–Organic Frameworks for Multimode Temperature Sensing with High Spatial Resolution

“…15−18 If each thermal readout differ, it indicates that the thermometer works abnormally. 19,20 Among various luminescent materials, organic dyes with different functional characteristics are sensitive to ambient temperature and are considered to be one of the best luminescent materials for constructing multiple temperature-dependent optical signals. However, the undesirable interactions between organic molecules, such as aggregation-induced quenching (ACQ) and energy transfer phenomena caused by Forster resonance, make it difficult to achieve sensitive and stable multiple optical signals output in the solid state.…”

“…They mostly work on single optical signal such as luminescent intensity, luminescent lifetime, maximum emission wavelength, or luminescent intensity ratio, which requires recalibration in a complex environment, because of different physicochemical characters between luminophores . A more reliable thermometer can be obtained by introducing multiple optical signals into a material through a mutual verification between the signals. − If each thermal readout differ, it indicates that the thermometer works abnormally. , Among various luminescent materials, organic dyes with different functional characteristics are sensitive to ambient temperature and are considered to be one of the best luminescent materials for constructing multiple temperature-dependent optical signals. However, the undesirable interactions between organic molecules, such as aggregation-induced quenching (ACQ) and energy transfer phenomena caused by Förster resonance, make it difficult to achieve sensitive and stable multiple optical signals output in the solid state. , These limitations have been overcome by encapsulating organic dyes into the pores of metal–organic frameworks (MOFs).…”