New Strategy for Circumventing the Limitation of Thermally Linked States and Boosting the Relative Thermal Sensitivity of Luminescence Ratiometric Thermometry

Abstract

Optical ratiometric thermometry, based on the luminescence of trivalent rare-earth ions, has attracted considerable attention because of its noncontact working pattern, short response time, and strong antidisturbance ability. However, conventional optical thermal detection, on the basis of thermally linked states, has a relatively low relative sensitivity. To circumvent the limitation, here, a new strategy for boosting the relative thermal sensitivity, especially at relatively high temperatures, is introduced. It depends on two totally different mechanisms which own the contrary temperature dependences. For one thing, when excited at 310 nm, the green luminescence originating from CaWO 4 :Tb 3+ phosphors increases monotonously because of the red shift of the charge-transfer band of the WO 4 2− group. For another, this luminescence shows decreasing tendency gradually upon being directly excited at 380 nm. Thus, the intensity ratio between the luminescence obtained at two different excitation conditions is exploited for optical thermometry with success. By using this strategy, the relative thermal sensitivity is as high as 0.71% K −1 at 783 K, which is increased by more than fourfold compared with the conventional method that depends on the thermally coupled states of the Er 3+ ion, which are the 2 H 11/2 and 4 S 3/2 states. Moreover, this value is also among the highest sensitivities reported so far for ratiometric thermal sensing. What is more, it has been demonstrated that the sensitivity can be adjusted easily by changing the excitation wavelength. Therefore, the work provides an effective strategy for boosting the thermal sensitivity for optical ratiometric thermometry, which contributes to highly sensitive thermal detection in the future.

Ratiometric Optical Thermometry in Lanthanide-Doped Molybdate Phosphors via Construction of Diverse Charge-Transfer Bands

“…As an important parameter in industry and scientific research, temperature has a variety of measurement methods. The contactless temperature measurement method established on the optical response of materials has higher temperature resolution and faster response speed than the traditional contact temperature measurement method and has been successfully applied in the fields of meteorology, military, and scientific research. − The principle of the temperature measurement method of fluorescence intensity ratio (FIR) is to calibrate the temperature by the relative ratio of the emission peaks in the spectrum. This method is not affected by the change of luminous intensity caused by other factors, so it has a broad application prospect. , The traditional FIR temperature measurement method is to measure the ratio of the fluorescence intensities of different thermal coupling energy levels in a single light-emitting center. − However, if the band gap between the thermal coupling energy levels is too large, the absolute sensitivity will be reduced, while if it is too small, the relative sensitivity will be reduced. , Therefore, this method of temperature measurement is detrimental to obtaining higher relative sensitivity and absolute sensitivity at the same time and affects the signal resolution.…”

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.…”

Deep-Tissue Temperature Sensing Realized in BaY2O4:Yb3+/Er3+ with Ultrahigh Sensitivity and Extremely Intense Red Upconversion Luminescence

“…Particularly, the FIR thermometry based on trivalent lanthanide ions doped upconversion (UC) phosphors have received extensive interest because of the potential application as a temperature sensor in vivo . − Typically, in order to achieve efficient UC emission and accurate temperature measurement, erbium ion Er 3+ with abundant ladder-like arranged energy levels, is often selected as the activator along with Yb 3+ as the sensitizer due to its large absorption cross section around 980 nm and efficient energy transfer (ET) to Er 3+ . − As a result, Er 3+ could usually generate intense green UC emission derived from 2 H 11/2 → 4 I 15/2 and 4 S 3/2 → 4 I 15/2 transitions under the excitation of 980 nm wavelength. Subsequently, the optical temperature sensing can be realized based on the FIR between the thermally coupled levels (TCLs) 2 H 11/2 and 4 S 3/2 . , However, its practical application is greatly limited by the strong absorption for green light in the biological tissues.…”