Next Article in Journal
Globular Flower-Like Reduced Graphene Oxide Design for Enhancing Thermally Conductive Properties of Silicone-Based Spherical Alumina Composites
Next Article in Special Issue
Comparison of Three Ratiometric Temperature Readings from the Er3+ Upconversion Emission
Previous Article in Journal
Green Silver Nanoparticles Formed by Phyllanthus urinaria, Pouzolzia zeylanica, and Scoparia dulcis Leaf Extracts and the Antifungal Activity
Previous Article in Special Issue
Synthesis, Cytotoxicity Assessment and Optical Properties Characterization of Colloidal GdPO4:Mn2+, Eu3+ for High Sensitivity Luminescent Nanothermometers Operating in the Physiological Temperature Range
Open AccessArticle

Making Nd3+ a Sensitive Luminescent Thermometer for Physiological Temperatures—An Account of Pitfalls in Boltzmann Thermometry

1
Condensed Matter and Interfaces, Debye Institute for Nanomaterials Science, Department of Chemistry, Utrecht University, Princetonplein 1, 3584 CC Utrecht, The Netherlands
2
Vinča Institute of Nuclear Sciences, University of Belgrade, 11001 Belgrade, Serbia
*
Author to whom correspondence should be addressed.
Nanomaterials 2020, 10(3), 543; https://doi.org/10.3390/nano10030543
Received: 22 February 2020 / Revised: 12 March 2020 / Accepted: 13 March 2020 / Published: 18 March 2020
(This article belongs to the Special Issue Luminescent Rare-Earth-Based Nanomaterials)
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. View Full-Text
Keywords: Nd3+; luminescence thermometry; in vivo imaging; Boltzmann equilibrium; time-resolved spectroscopy Nd3+; luminescence thermometry; in vivo imaging; Boltzmann equilibrium; time-resolved spectroscopy
Show Figures

Graphical abstract

MDPI and ACS Style

Suta, M.; Antić, Ž.; Ðorđević, V.; Kuzman, S.; Dramićanin, M.D.; Meijerink, A. Making Nd3+ a Sensitive Luminescent Thermometer for Physiological Temperatures—An Account of Pitfalls in Boltzmann Thermometry. Nanomaterials 2020, 10, 543.

Show more citation formats Show less citations formats
Note that from the first issue of 2016, MDPI journals use article numbers instead of page numbers. See further details here.

Article Access Map by Country/Region

1
Back to TopTop