Chiroptically Active Multi-Modal Calcium Carbonate-Based Nanocomposites

The development of multimodal nano- and micro-structures has become an increasingly popular area of research in recent years. In particular, the combination of two or more desirable properties within a single structure opens multiple opportunities from biomedicine, sensing, and catalysis, to a variety of optical applications. Here, for the first time, we report the synthesis and characterization of multimodal chiroptically active CaCO3 nanocomposites. These composites have been prepared by a modified microemulsion method in the presence of an amino acid (cysteine). Following this, additional modalities have been introduced by loading the composites with luminescent nanoparticles or doping with Eu3+ ions. The luminescent composites have been produced by the incorporation of CuInZnS/ZnS or CdSe@ZnS/ZnS core/shell quantum dots, or via doping with trivalent europium. In this manner, we have produced chiroptically active composites with orange, green, and red luminescence. Overall, this work demonstrates the unique advantage and potential of our approach and new class of chiroptically active CaCO3 nanocomposites, which display tunable functionality to specific requirements via the incorporation of desired ions, nanoparticles, and chirality of the structure.

Designing Optical Thermometers Using Down/Upconversion Ca14Al10Zn6O35: Ti4+, Eu3+/Yb3+, Er3+ Thermosensitive Phosphors

Down/upconversion Ca₁₄Al₁₀Zn₆O₃₅ inorganic phosphors codoped with Ti⁴⁺/Eu³⁺ or Yb³⁺/Er³⁺ were prepared. The crystal structure and downconversion luminescence properties of Ca₁₄Al₁₀Zn₆O₃₅:Ti⁴⁺, Eu³⁺ phosphors were studied in detail. Ti⁴⁺ and Eu³⁺ occupied Al³⁺ and Ca²⁺ sites in the host lattice, respectively. Under the excitation of 273 nm, the emission peak in the 300-570 nm band originated from the ²T₂ → O^2- transition of Ti⁴⁺. The f-f transition of Eu³⁺ ions generated multiple peaks in the 570-800 nm range. The emission intensity of Ti⁴⁺ and Eu³⁺ ions can be used as a fluorescence intensity ratio (FIR) signal. Based on the FIR technology, the maximum relative sensitivity (S_r) and the minimum temperature uncertainty (δT) reached 1.41% K^-1 and 0.07 K, respectively. Meanwhile, the temperature-sensing behaviors were explored by the temperature-dependent upconversion spectra of Er³⁺- and Yb³⁺-codoped Ca₁₄Al₁₀Zn₆O₃₅ phosphors. Based on the fluorescence intensity ratio of thermal coupling levels (Er³⁺:²H_11/2/⁴S_3/2), the maximum S_r and minimum δT of upconversion phosphors reached 1.28% K^-1 and 0.08 K in the temperature range of 293-473 K, respectively. Ca₁₄Al₁₀Zn₆O₃₅:Ti⁴⁺/Eu³⁺ (Yb³⁺/Er³⁺) phosphors realize temperature sensors with higher relative sensitivity, and it is a good candidate material for optical temperature measurement.