3139wileyonlinelibrary.com discriminable emission peaks as the monitored signals, and to suppress absolute and relative detecting errors, high absolute and relative temperature sensitivities are required.In this aspect, conventional investigations focus on the thermally coupled level pairs (TCL) of rare earth ions (for example, 2 H 11/2 and 4 S 3/2 level for Er
3+). [7][8][9][10][11][12][13][14][15] Typically, with variation of temperature, population in the upper and lower levels of TCL would change oppositely, inducing variation in FIR of these two levels. For this type of temperature sensing materials, a narrow energy gap between TCL would favor the absolute temperature sensitivity ( S a ), but be harmful to the relative temperature sensitivity ( S r ). In addition, the narrow energy gap would induce overlap of the two monitored emission peaks, resulting in an inferior signal discriminability. [ 9,12 ] In contract, a wide energy gap between TCL would benefi t S r and the signal discriminability, but weaken the thermal coupling of TCL, leading to a low S a . [ 13,15 ] Generally speaking, in the TCL-based optical thermometry, simultaneously promoting S a , S r and signal discriminability is almost impossible.Other kinds of thermometry strategy have also been introduced into the optical thermometric technique. For example, the phonon assisted energy transfer between Eu 3+ and Tb 3+ ions has been utilized in optical thermometry. [16][17][18][19] However, this kind of thermometry is usually applicable only at temperature below 320 K. Nanocomposites containing quantum dots and rare earth ions have also been applied as thermometric materials relying on the different thermal quenching behaviors of quantum dots and rare earth ions. [ 20,21 ] However, FIR of these materials is easily infl uenced by other environment parameters (such as pH value), which would introduce error in temperature detection. Apparently, searching for new thermometry strategy to develop high-performance luminescent temperature sensing materials is highly desired.In previous studies, the metal-to-metal intervalence charge transfer (IVCT) processes between lanthanide (Pr 3+ or Tb 3+ ) and d 0 electron confi gured transition metal ions (Ti 4+ , V 5+ , Nb 5+ , Mo 6+ , or W 6+ ) in oxide crystals have been demonstrated to be an effective pathway to excite the corresponding lanthanide ions. [22][23][24][25][26] Moreover, IVCT can provide an effi cient quenching
A Novel Optical Thermometry Strategy Based on Diverse Thermal Response from Two Intervalence Charge Transfer StatesYan Gao , Feng Huang , * Hang Lin , Jiangcong Zhou , Ju Xu , and Yuansheng Wang * In this work, a novel thermometry strategy based on the diversity in thermal quenching behavior of two intervalence charge transfer (IVCT) states in oxide crystals is proposed, which provides a promising route to design selfreferencing optical temperature sensing material with superior temperature sensitivity and signal discriminability.
