Nd³⁺doped Gd₃Sc₂Al₃O₁₂nanoparticles: towards efficient nanoprobes for temperature sensing

Abstract

Higher synthesis temperature of GSAG:Nd3+ nanocrystals results in enhanced relative thermal sensitivity (Sr) as well as coherence length (Lc).

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

“…The present results show promising potential of Nd 3+ for physiological temperature sensing by means of luminescence thermometry, if the boundary conditions for the validity of a Boltzmann equilibrium are met which requires low Nd 3+ concentrations. The 4 F5/2 -4 F3/2 spin-orbit gap in Nd 3+ gives rise to relative sensitivities that are an order of magnitude higher than the typically found ones in the range of 0.25% K −1 [50]. A disadvantage of the presented thermometric concept of Nd 3+ is the rather low intensity of the 4 F5/2 → 4 I9/2 emission that can give rise to a higher relative intensity uncertainty, depending on the sensitivity of the detection system.…”

“…Among the various possibilities of synthetically well accessible and size-controllable nanocrystals such as fluorides [46][47][48], nanosized garnets have become especially interesting in that sense due to the well resolved and intense 4 F 3/2 (R 1,2 ) → 4 I 9/2 (Z 5 ) emissive transitions at 935 nm and 945 nm. This allowed researchers to tune the relative thermal sensitivity S r of this particular LIR towards the theoretically expected maximum value of around 0.15% K −1 at 37 • C according to the given energy gap [49,50]. The value obtained with that concept of Nd 3+ -based nanothermometry could only be exceeded in lattices with higher crystal field splitting, for example LiLuF 4 nanocrystals, with a value of around 0.5% K −1 at 37 • C [51].…”

“…Figure 10 depicts the evolution of the relative sensitivity for La 0.999 Nd 0.001 PO 4 as obtained from Equation (7). In particular, it is higher than 1% K −1 for the full physiological temperature regime (30 • C-75 • C), which is practically difficult to achieve around room temperature with any single ion Boltzmann thermometer, especially in the NIR regime [49][50][51]57]. Typically, energy transfer-based thermometers are used in those cases [30,43,54,55] for which the underlying thermometric mechanisms are often not well established.…”

“…Temperature evolution of the relative sensitivity of Nd 3+ in La 0.999 Nd 0.001 PO 4 within the Boltzmann validity regime and upon usage of the 4 F 5/2 -4 F 3/2 gap for Boltzmann-based luminescence thermometry. The grey dashed line indicates the desirable minimum relative sensitivity for in vivo luminescence thermometry, while the blue dashed regime marks the reported maximum achievable relative sensitivity for thermal coupling between the Kramers' doublets of the 4 F 3/2 spin-orbit level [49][50][51].…”

Dual light-emitting Yb3+,Er3+-doped La(IO3)3 iodate nanocrystals: up-conversion and second harmonic generation

“…4 For in vivo experiments, penetration depth is a crucial parameter 5 and the use of emitters with excitation properties in the near-infrared (NIR) region and the so-called biological transparency windows (BWs) is required. Based on down-conversion fluorescence, Nd 3+ -doped fluorescence probes 6,7 or more complex multi-doped architectures 8,9 have raised high interest with their excitation at 808 nm and their emission in the first (750 -950 nm), second (1000 -1350 nm) and third (1500 -1800 nm) BWs, ensuring deep tissue imaging while minimizing tissue autofluorescence and photon scattering. Similarly, PbS or InP Quantum Dots appear as good candidates for biological applications thanks to their tunable NIR emission.…”