Nowadays,
the construction of photothermal therapy (PTT) agents
integrated with real-time thermometry for cancer treatment in deep
tissues has become a research hotspot. Herein, an excellent photothermal
conversion material, BaY2O4: Yb3+/Nd3+, assembled with real-time optical thermometry is
developed successfully. Ultrasensitive temperature sensing is implemented
through the fluorescence intensity ratio of thermally coupled Nd3+: 4F
j
(j = 7/2, 5/2, and 3/2) with a maximal absolute and relative sensitivity
of 68.88 and 3.29% K–1, respectively, which surpass
the overwhelming majority of the same type of thermometers. Especially,
a thermally enhanced Nd3+ luminescence with a factor of
180 is detected with irradiation at 980 nm, resulting from the improvement
in phonon-assisted energy transfer efficiency. Meanwhile, the photothermal
conversion performance of the sample is excellent enough to destroy
the pathological tissues, of which the temperature can be raised to
319.3 K after 180 s of near-infrared (NIR) irradiation with an invariable
power density of 13.74 mW/mm2. Besides, the NIR emission
of Nd3+ can reach a depth of 7 mm in the biological tissues,
as determined by an ex vivo experiment. All the results show the potential
application of BaY2O4: Yb3+/Nd3+ as a deep-tissue PTT agent simultaneously equipped with
photothermal conversion and temperature sensing function.
The occurrence of energy transfer (ET) would enhance
the luminescence
of the activator but sacrifice that of the sensitizer. However, the
novel Sm3+-doped Ca2TbSn2Al3O12 (CTSAO) phosphor reported here seems to be an exception.
In the series of CTSAO:xSm3+ phosphors
investigated, something unexpected occurs; the activator, Sm3+, did not gain any energy compensation from the sensitizer, Tb3+, when temperature increases. Instead, when the loss of Sm3+ luminescence accelerates, simultaneously, the loss of Tb3+ luminescence accordingly alleviates. By careful calculations
on the ET efficiency of the CTSAO:0.06Sm3+ phosphor at
different temperatures, it is surprisingly found that the efficiency
keeps decreasing as temperature increases. It means that the Tb3+–Sm3+ energy transfer is capable of being
interrupted by an increasing temperature. By simulation, it is found
that the occurrence of thermal interruption of energy transfer benefits
the achievement of a higher temperature sensing sensitivity. In this
sense, making use of the thermal interruption of energy transfer could
become a novel route for further design of the fluorescence intensity
ratio-type luminescence thermometers.
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