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Making Nd3+ a Sensitive Luminescent Thermometer for Physiological Temperatures—An Account of Pitfalls in Boltzmann Thermometry.
- Source :
-
Nanomaterials (2079-4991) . Mar2020, Vol. 10 Issue 3, p543. 1p. - Publication Year :
- 2020
-
Abstract
- Ratiometric luminescence thermometry employing luminescence within the biological transparency windows provides high potential for biothermal imaging. Nd3+ is a promising candidate for that purpose due to its intense radiative transitions within biological windows (BWs) I and II and the simultaneous efficient excitability within BW I. This makes Nd3+ almost unique among all lanthanides. Typically, emission from the two 4F3/2 crystal field levels is used for thermometry but the small ~100 cm−1 energy separation limits the sensitivity. A higher sensitivity for physiological temperatures is possible using the luminescence intensity ratio (LIR) of the emissive transitions from the 4F5/2 and 4F3/2 excited spin-orbit levels. Herein, we demonstrate and discuss various pitfalls that can occur in Boltzmann thermometry if this particular LIR is used for physiological temperature sensing. Both microcrystalline, dilute (0.1%) Nd3+-doped LaPO4 and LaPO4: x% Nd3+ (x = 2, 5, 10, 25, 100) nanocrystals serve as an illustrative example. Besides structural and optical characterization of those luminescent thermometers, the impact and consequences of the Nd3+ concentration on their luminescence and performance as Boltzmann-based thermometers are analyzed. For low Nd3+ concentrations, Boltzmann equilibrium starts just around 300 K. At higher Nd3+ concentrations, cross-relaxation processes enhance the decay rates of the 4F3/2 and 4F5/2 levels making the decay faster than the equilibration rates between the levels. It is shown that the onset of the useful temperature sensing range shifts to higher temperatures, even above ~ 450 K for Nd concentrations over 5%. A microscopic explanation for pitfalls in Boltzmann thermometry with Nd3+ is finally given and guidelines for the usability of this lanthanide ion in the field of physiological temperature sensing are elaborated. Insight in competition between thermal coupling through non-radiative transitions and population decay through cross-relaxation of the 4F5/2 and 4F3/2 spin-orbit levels of Nd3+ makes it possible to tailor the thermometric performance of Nd3+ to enable physiological temperature sensing. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 20794991
- Volume :
- 10
- Issue :
- 3
- Database :
- Academic Search Index
- Journal :
- Nanomaterials (2079-4991)
- Publication Type :
- Academic Journal
- Accession number :
- 142524850
- Full Text :
- https://doi.org/10.3390/nano10030543