We
demonstrate a potential optical thermometric material, Pr3+-doped triple-layered perovskite Na2La2Ti3O10 microcrystals, which promises a remarkable
performance in temperature sensing over a wide temperature range (125–533
K), with a maximum relative sensitivity of 2.43% K–1 at 423 K. Both temperature and high-pressure dependent photoluminescence
measurements were performed for this compound. It turns out that the
Pr3+–Ti4+ intervalence charge transfer
state is the primary cause for the very efficient thermometric characteristics
in the 296–533 K range. In the 125–300 K range, 3P1 and 3P0 levels of Pr3+ can be exploited as thermally coupled energy levels for
temperature sensing with high sensitivity at and below room temperature.
A significant enhancement of the Pr3+ ions’ luminescence
observed in the 4.5–300 K range is ascribed to an efficient,
thermally activated energy transfer process from the host to Pr3+ ions. Carrier recombination on Pr3+ related hole
traps was proposed in the studied system. The thermoluminescence properties
are investigated, and possible mechanisms for the interpretation of
the experimental results are discussed as well. This work may provide
a perspective approach to design a high-performance, self-calibrated
optical thermometer operating over a wide temperature range.
Laser-induced white emission of diamond was investigated under irradiation with a focused beam of an infrared laser diode. It is a surface-related coherent emission, characterized by an excitation threshold and an exponential dependence on pumping laser power. The mechanism of white emission is discussed in terms of multiphoton ionization of carbon atoms in an irradiated spot. The excitation power dependence of white emission intensity has demonstrated hysteresis loop behavior. This phenomenon could be useful in new broadband laser sources and optical information storage.
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