A broadening temperature sensitivity range with a core-shell YbEr@YbNd double ratiometric optical nanothermometer.

The chemical architecture of lanthanide doped core-shell up-converting nanoparticles can be engineered to purposely design the properties of luminescent nanomaterials, which are typically inaccessible to their homogeneous counterparts. Such an approach allowed to shift the up-conversion excitation wavelength from ∼980 to the more relevant ∼808 nm or enable Tb or Eu up-conversion emission, which was previously impossible to obtain or inefficient. Here, we address the issue of limited temperature sensitivity range of optical lanthanide based nano-thermometers. By covering Yb-Er co-doped core nanoparticles with the Yb-Nd co-doped shell, we have intentionally combined temperature dependent Er up-conversion together with temperature dependent Nd → Yb energy transfer, and thus have expanded the temperature response range ΔT of a single nanoparticle based optical nano-thermometer under single ∼808 nm wavelength photo-excitation from around ΔT = 150 K to over ΔT = 300 K (150-450 K). Such engineered nanocrystals are suitable for remote optical temperature measurements in technology and biotechnology at the sub-micron scale.

O2(a1Δg) + Mg, Fe, and Ca: experimental kinetics and formulation of a weak collision, multiwell master equation with spin-hopping.

The first excited electronic state of molecular oxygen, O(2)(a(1)Δ(g)), is formed in the upper atmosphere by the photolysis of O(3). Its lifetime is over 70 min above 75 km, so that during the day its concentration is about 30 times greater than that of O(3). In order to explore its potential reactivity with atmospheric constituents produced by meteoric ablation, the reactions of Mg, Fe, and Ca with O(2)(a) were studied in a fast flow tube, where the metal atoms were produced either by thermal evaporation (Ca and Mg) or by pulsed laser ablation of a metal target (Fe), and detected by laser induced fluorescence spectroscopy. O(2)(a) was produced by bubbling a flow of Cl(2) through chilled alkaline H(2)O(2), and its absolute concentration determined from its optical emission at 1270 nm (O(2)(a(1)Δ(g) - X(3)Σ(g) (-)). The following results were obtained at 296 K: k(Mg + O(2)(a) + N(2) → MgO(2) + N(2)) = (1.8 ± 0.2) × 10(-30) cm(6) molecule(-2) s(-1); k(Fe + O(2)(a) → FeO + O) = (1.1 ± 0.1) × 10(-13) cm(3) molecule(-1) s(-1); k(Ca + O(2)(a) + N(2) → CaO(2) + N(2)) = (2.9 ± 0.2) × 10(-28) cm(6) molecule(-2) s(-1); and k(Ca + O(2)(a) → CaO + O) = (2.7 ± 1.0) × 10(-12) cm(3) molecule(-1) s(-1). The total uncertainty in these rate coefficients, which mostly arises from the systematic uncertainty in the O(2)(a) concentration, is estimated to be ±40%. Mg + O(2)(a) occurs exclusively by association on the singlet surface, producing MgO(2)((1)A(1)), with a pressure dependent rate coefficient. Fe + O(2)(a), on the other hand, shows pressure independent kinetics. FeO + O is produced with a probability of only ∼0.1%. There is no evidence for an association complex, suggesting that this reaction proceeds mostly by near-resonant electronic energy transfer to Fe(a(5)F) + O(2)(X). The reaction of Ca + O(2)(a) occurs in an intermediate regime with two competing pressure dependent channels: (1) a recombination to produce CaO(2)((1)A(1)), and (2) a singlet∕triplet non-adiabatic hopping channel leading to CaO + O((3)P). In order to interpret the Ca + O(2)(a) results, we utilized density functional theory along with multireference and explicitly correlated CCSD(T)-F12 electronic structure calculations to examine the lowest lying singlet and triplet surfaces. In addition to mapping stationary points, we used a genetic algorithm to locate minimum energy crossing points between the two surfaces. Simulations of the Ca + O(2)(a) kinetics were then carried out using a combination of both standard and non-adiabatic Rice-Ramsperger-Kassel-Marcus (RRKM) theory implemented within a weak collision, multiwell master equation model. In terms of atmospheric significance, only in the case of Ca does reaction with O(2)(a) compete with O(3) during the daytime between 85 and 110 km.