Luminescence thermometry alleviates the difficulties associated with conventional methods for thermal sensing and provides outstanding opportunities for non-contact thermometry with high sensitivity and resolution.
Trivalent bismuth is a popular main group ion showing
versatile
luminescent behaviors in a broad spectral range from ultraviolet to
visible, but barely in the near-infrared (NIR) region. In this study,
we have observed unexpected NIR emission at ∼744 nm in a Bi3+-doped pyrochlore, Y2Ti2O7 (YTOB). Our first-principles electronic structure calculation and
analysis of the Bi local structure via extended X-ray absorption fine
structure indicate that only Bi3+ species appears in YTOB
and it has a similar local environment to that of Y3+.
The NIR emission is assigned to a Ti4+ → Bi3+ metal-to-metal charge transfer process. Moreover, we have
demonstrated dual-mode luminescence thermometry based on the luminescence
intensity ratio (LIR) and lifetime (τ) in 0.5% Bi3+ and 0.5% Pr3+ co-doped Y2Ti2O7 (YTOB0.5P0.5). It exhibits high thermometric sensitivity
simultaneously in the cryogenic temperature range from 78 to 298 K
based on τ of the NIR emission of Bi3+ at 748 nm
and in the temperature range of 278–378 K based on the LIR
of Bi3+ to Pr3+ emissions (I
748/I
615). As a novel LIR-τ
dual-mode thermometric material over a wide temperature range, the
maximum relative sensitivities of the YTOB0.5P0.5 reach 3.53% K–1 at 298 K from the τ mode and 3.52% K–1 at 318 K based on the LIR mode. The dual-mode luminescence thermometry
with high responsivity from our Bi3+-based pyrochlore Y2Ti2O7 phosphor opens a new avenue for
more luminescent materials toward multi-mode thermometry applied in
complex temperature-sensing conditions.
Thermal quenching (TQ) is a major challenge facing many phosphors, especially those used in the high-temperature range. To overcome this obstacle, here we present a new phenomenon of excitation-wavelength-dependent antithermal quenching (anti-TQ) luminescence over a broad temperature range. We have observed that the luminescence intensity of Eu 3+ -doped Sc 2 Mo 3 O 12 almost triples at elevated temperatures along with intensified energy transfer from the host to the dopant upon excitation at the charge-transfer band of 277 nm. Specifically, the absolute emission intensity of Sc 2 Mo 3 O 12 :20%Eu 3+ measured at 398 and 798 K reaches 292% and 97% of its initial intensity taken at 298 K, respectively. Similar to the photoluminescence emission intensity, the lifetime also elongates upon heating with a maximum value at 623 K. We have unveiled the mechanism of the excitation-wavelength-dependent anti-TQ luminescence, which is attributed to the promoted energy transfer induced by the negative thermal expansion (NTE) property of the Sc 2 Mo 3 O 12 host. Moreover, we have demonstrated the efficient high-temperature luminescence thermometric performance of this anti-TQ luminescence phosphor using its temperature-dependent lifetime. The new phenomenon and experimental findings presented in this study provide inspiration for the future exploration of NTE-based phosphors with thermally enhanced luminescence performance via their intensified energy transfer for broad potential applications.
Radionuclides and heavy metal ions have become the main harmful pollutants in the environment. Developing sensitive and rapid methods to detect them from natural or waste waters is important to...
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