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Rare earth (RE) doped inorganic nanocrystals have been demonstrated as efficient contrast agents for deep tissue shortwave-infrared (SWIR) imaging with high sensitivities leading to potential early detection of tumors. However, a potential concern is the unknown long-term toxicity and incompatibility of inorganic nanocrystals. In this work, biodegradable rare earth nanocrystals of Nd doped SrFCl coated with polydopamine (SrFCl:Nd@PDA) were designed. Instead of traditional fluoride hosts, the chlorinated SrF2 (i.e. SrFCl) with low phonon energy which significantly improved the brightness of SrFCl:Nd in the SWIR region was used as the host. After coating with a NIR-absorptive PDA layer, the SrFCl:Nd nanoparticles serve as not only a contrast agent for photoacoustic imaging, but also a potential photothermal agent for cancer therapy. Moreover, these SrFCl:Nd@PDA nanoparticles can be rapidly and completely degraded in phosphate buffer solution within 1 h, which effectively addresses the concerns of the deleterious effects arising from potential long term accumulation. The increased accumulation and retention at tumor sites, and complete in vivo clearance ∼6 h after injection make these SrFCl:Nd@PDA nanoparticles a promising degradable phototheranostic agent.

In this work, we report a detailed study of the synthesis of sub-micron sized Gd2O2S spheres using a two-step process: (1) amorphous precursor synthesis using the solvothermal method where a surfactant was used to control particle morphology, followed by (2) crystallization to form Gd2O2S polycrystalline spheres in a sulfur-rich environment. The crystallization and sulfurization processes are investigated by monitoring the crystal growth at different temperatures and under different environments using mainly X-ray diffraction and analysis of the precursor's thermal decomposition profile. The optical emissions of the Er and Yb-Er doped Gd2O2S upon excitation at 975 nm were investigated to identify the optimal dopant concentrations, optimal heat treatment temperature as well as to further elucidate any fine structure changes. Our results also show that the maximum emission intensities were obtained for a heat treatment temperature of 800 °C, where increased dopant diffusion coupled with non-uniform surface segregation at much higher temperatures led to non-uniform dopant distribution and reduced emission intensities. Our findings from these studies would be useful towards the synthesis of brightly-emitting Gd2O2S based luminescent materials as well as for the controlled gas-aided sulfurization of other metal oxysulfides.

The recent emergence of wearable electronics has driven the advancements of flexible and elastic conductive metal–polymer composites as electrodes and sensors. Surface modification of the conductive metal fillers are required to achieve a good dispersion within the matrix to obtain suitable conductivity and sensing properties. Additionally, it would be critical to ensure that the inclusion of these fillers does not affect the curing of the pre-polymers so as to ensure sufficient filler loading to form functional composites. In this work, a one-step approach is used to modify Ag–PAA nanoparticles via hydrogen bonds to form PAA–PVP complex modified Ag nanoparticles. The interfacial characteristics and thermal stability of these surface-modified Ag nanoparticles were studied to elucidate the underlying chemistries that governed the surface modification process. After surface modification, we successfully improved the dispersion of Ag nanoparticles and enabled curing of PDMS to higher Ag loadings of ∼25 vol%, leading to much lower electrical resistivity of ∼6 Ω cm. Our studies also showed that Ag nanoparticles modified at a PAA/PVP molar ratio of 1 : 10 resulted in a minimal particle aggregation. In a preliminary testing of our conductive composites as electrodes, clear electrocardiography signals were obtained. The facile surface modification method introduced here can be adapted for other systems to modify the particle interfacial behavior and improve the filler dispersion and loading without adversely affecting the polymer curing chemistry.

Erbium (Er) doped CaF2 nanophosphors with enhanced short-wavelength infrared light (SWIR) emission synthesized in this work have promising potential for biomedical applications in diagnostics and deep tissue imaging due to their low vibrational energy, large optical transparency and superior biocompatibility. For deep tissue imaging application, it is critical to achieve highly emissive SWIR emitting CaF2 nanophosphors to enhance detection resolution and depth using the “tissue-transparent window”. In this work, we demonstrate substantial enhancement in the IR emission of CaF2 nanocrystals using a tri-doping scheme of ytterbium (Yb), erbium (Er) and cerium (Ce). The effects of Er, Ce and Yb dopant concentration on the IR emission intensity was systematically studied and the optimum Er, Ce and Yb dopant concentration was estimated to be ∼2, ∼10 and ∼20 mol%, respectively. At Yb 20 mol%, the IR emission intensity was increased ∼12 fold by optimizing the Ce dopant concentration.

In this work, we report a detailed study of the synthesis of sub-micron sized Gd2O2S spheres using a two-step process: (1) amorphous precursor synthesis using the solvothermal method where a surfactant was used to control particle morphology, followed by (2) crystallization to form Gd2O2S polycrystalline spheres in a sulfur-rich environment. The crystallization and sulfurization processes are investigated by monitoring the crystal growth at different temperatures and under different environments using mainly x-ray diffraction and analysis of the precursor’s thermal decomposition profile. The optical emissions of the Er and Yb-Er doped Gd2O2S upon excitation at 975 nm were investigated to identify the optimal dopant concentrations, optimal heat treatment temperature as well as to further elucidate any fine structure changes. Our results also show that the maximum emission intensities were obtained for a heat treatment temperature of 800 °C, where increased dopant diffusion coupled with non-uniform surface segregation at much higher temperatures led to non-uniform dopant distribution and reduced emission intensities. Our findings from these studies would be useful towards the synthesis of brightly-emitting Gd2O2S based luminescent materials as well as for the controlled gas-aided sulfurization of other metal oxysulfides.