| Summary: | The sensitivity of luminescent Boltzmann thermometers is restricted by the energy difference between the thermally coupled excitement levels of trivalent lanthanides, and their values further decrease with increases in temperature, rendering their use at high temperatures difficult. Here, we demonstrate how to overcome this sensitivity limitation by employing multiparameter and multilevel cascade temperature readings. For this purpose, we synthesized Dy<sup>3+</sup>:Y<sub>2</sub>SiO<sub>5</sub>, a phosphor whose emission is known to begin quenching at very high temperatures. Its photoluminescence-emission features, later used for thermometry, consisted of two blue emission bands centered around 486 nm and 458 nm, and two bands centered around 430 nm and 398 nm, which were only visible at elevated temperatures. Next, we performed thermometry using the standard luminescence-intensity ratio (LIR) method, which employs the <sup>4</sup>F<sub>9/2</sub> and <sup>4</sup>I<sub>15/2</sub> Dy<sup>3+</sup> levels’ emissions and the multilevel cascade method, which additionally uses the <sup>4</sup>G<sub>11/2</sub> level and overlapping intensities of <sup>4</sup>I<sub>13/2</sub>, <sup>4</sup>M<sub>21/2</sub>, <sup>4</sup>K<sub>17/2</sub>, and <sup>4</sup>F<sub>7/2</sub> levels to create two LIRs with a larger energy difference than the standard LIR. This approach yielded a sensitivity that was 3.14 times greater than the standard method. Finally, we simultaneously exploited all the LIRs in the multiparameter temperature readings and found a relative sensitivity that was 30 times greater than that of the standard approach.
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