Near infrared absorbing near infrared emitting highly-sensitive luminescent nanothermometer based on Nd³⁺ to Yb³⁺ energy transfer

Abstract

A new type of near infrared absorbing near infrared emitting (NANE) luminescent nanothermometer is presented, with a physical background that relies on efficient Nd(3+) to Yb(3+) energy transfer under 808 nm photo-excitation. The emission spectra of LiLa0.9-xNd0.1YbxP4O12 (x = 0.05, 0.1, 0.2, 0.3, 0.5) nanocrystals were measured in a wide 100-700 °C temperature range. The ratio between the Nd(3+) ((4)F3/2→(4)I9/2) and Yb(3+) ((2)F5/2→(2)F7/2) luminescence bands, and the thermometer sensitivity were found to be strongly dependent on the Yb(3+) concentration. These phenomenological relations were discussed in terms of the competition between three phenomena, namely (a) Nd(3+)→ Yb(3+) phonon assisted energy transfer, (b) Yb(3+)→ Nd(3+) back energy transfer and (c) energy diffusion between Yb(3+) ions. The highest sensitivity of the temperature measurement was found for x = 0.5 (LiLa0.4Nd0.1Yb0.5P4O12), which was equal to 4 × 10(-3) K(-1) at 330 K. In stark contrast to conventional approaches, the proposed phosphate host matrix allows for a high level of doping, and thus, owing to the negligible concentration quenching, the presented luminophores exhibit a high absorption cross section and bright emission. Moreover, such optical remote thermometers, whose excitation and emission wavelengths are weakly scattered or absorbed and fall into the optical transmission window of the skin, may therefore become a practical solution for biomedical applications, such as remote control of thermotherapy.

Lanthanide‐Based Thermometers: At the Cutting‐Edge of Luminescence Thermometry

“…Several Ln 3+ pairs were used for DS nanothermometry, such as Tb 3+ /Eu 3+ , Nd 3+ /Yb 3+ , and Tm 3+ /Ho 3+ . However, most of the examples discussed in recent years are based on Nd 3+ , driven by potential bioimaging applications .…”

“…Ln 3+ ‐based materials are stable and narrow band emitters covering the entire electromagnetic spectrum with, in general, high emission quantum yields (>50% in the visible) . In the last decade, many Ln 3+ ‐based thermometers have been reported covering a wide temperature range, from cryogenic ( T < 100 K) to physiological (298–323 K) values, and including chelate complexes, metal organic frameworks (MOFs), polymers, organic–inorganic hybrids, upconverting, downconverting, and downshifting nanoparticles (NPs), and multifunctional heater‐thermometer nanoplatforms . The implementation of these Ln 3+ ‐based phosphors as ratiometric thermometers in diverse applications was extensively revised in the past decade, including in two books…”

Infrared‐Emitting QDs for Thermal Therapy with Real‐Time Subcutaneous Temperature Feedback

“…-260-27 Spectral ratio [6] Nd:YAG 808 940 0.15 10-70 Spectral ratio [7] NaYF4:Nd 830 870 0.12 0-150 Spectral ratio [8] LaF3:Nd 808 870 0.1 10-60 Spectral ratio [9] LiLaP4O12: Nd,Yb 808 890, 980 0.4 150-600 Spectral ratio [10] BW-II PLGA hybrid nanostructures 808 1064, 1270 2.5 10-55 Spectral ratio [11] LaF3:Nd,Yb 790 1064, 1300 0.1 10-50 Spectral ratio [12] Nd@YbLaF3 core/shell NPs 790 1064, 1300 0.41 10-50 Spectral ratio [12] Yb@NdLaF3 core/shell NPs 790 1064, 1300 0.36 10-50 Spectral ratio [12] PbS/CdS/ZnS QDs 808 1270 1 10-60 Intensity This work Table S1. Properties of different temperature-sensitive fluorescent nanosized systems.…”

“…[10] 4 However, other NPs, including carbon nanotubes, [11] graphene NPs, [12] and neodymium-doped NPs,13 [13] also present a remarkable photothermal conversion efficiency and, additionally, provide a near-infrared (NIR) fluorescence signal which can be used to track the location of the NPs inside the body. Furthermore, fluorescent NPs can provide additional functionalities, such as intratumoral temperature sensing.…”

Nd 3+ ions in nanomedicine: Perspectives and applications

“…Another strategy to improve the thermal sensitivity of Nd 3þ ion based NPs is codoping with Yb 3þ ions. In this respect, L. Marciniak et al have reported on thermal sensitivities in the NIR as high as 4 Â 10 À3 K À1 by means of back and forth energy transfer between Nd 3þ and Yb 3þ dopants in LiLaP 4 O 12 :Nd 3þ ,Yb 3þ NPs [68]. They systematically studied the effect of temperature on these transfer processes to conclude that the intensity ratio between the Nd 3þ ( 4 F 3/2 / 4 I 9/2 ) and Yb 3þ ( 2 F 5/2 / 2 F 7/2 ) emissions is highly sensitive to temperature changes.…”