Ferrielectricity in the Archetypal Antiferroelectric, PbZrO3.

Antiferroelectric materials, where the transition between antipolar and polar phase is controlled by external electric fields, offer exceptional energy storage capacity with high efficiencies, giant electrocaloric effect, and superb electromechanical response. PbZrO3 is the first discovered and the archetypal antiferroelectric material. Nonetheless, substantial challenges in processing phase pure PbZrO3 have limited studies of the undoped composition, hindering understanding of the phase transitions in this material or unraveling the controversial origins of a low-field ferroelectric phase observed in lead zirconate thin films. Leveraging highly oriented PbZrO3 thin films, a room-temperature ferrielectric phase is observed in the absence of external electric fields, with modulations of amplitude and direction of the spontaneous polarization and large anisotropy for critical electric fields required for phase transition. The ferrielectric state observations are qualitatively consistent with theoretical predictions, and correlate with very high dielectric tunability, and ultrahigh strains (up to 1.1%). This work suggests a need for re-evaluation of the fundamental science of antiferroelectricity in this archetypal material.

Maximizing Information: A Machine Learning Approach for Analysis of Complex Nanoscale Electromechanical Behavior in Defect-Rich PZT Films.

Scanning Probe Microscopy (SPM) based techniques probe material properties over microscale regions with nanoscale resolution, ultimately resulting in investigation of mesoscale functionalities. Among SPM techniques, piezoresponse force microscopy (PFM) is a highly effective tool in exploring polarization switching in ferroelectric materials. However, its signal is also sensitive to sample-dependent electrostatic and chemo-electromechanical changes. Literature reports have often concentrated on the evaluation of the Off-field piezoresponse, compared to On-field piezoresponse, based on the latter's increased sensitivity to non-ferroelectric contributions. Using machine learning approaches incorporating both Off- and On-field piezoresponse response as well as Off-field resonance frequency to maximize information, switching piezoresponse in a defect-rich Pb(Zr,Ti)O3 thin film is investigated. As expected, one major contributor to the piezoresponse is mostly ferroelectric, coupled with electrostatic phenomena during On-field measurements. A second component is electrostatic in nature, while a third component is likely due to a superposition of multiple non-ferroelectric processes. The proposed approach will enable deeper understanding of switching phenomena in weakly ferroelectric samples and materials with large chemo-electromechanical response.

Doped quantum dot@silica nanocomposites for white light-emitting diodes.

This work reports the use of a near-UV-LED chip in combination with blue, green-yellow and red emitting doped ZnSe QD@silica nanocomposites to construct a novel WLED with reduced scattering and no reabsorption. Blue, green-yellow and red emitting Cu or Mn doped ZnSe QDs with enlarged Stokes shifts and similar absorption peaks (360-410 nm) were synthesized in liquid paraffin in order to solve the reabsorption problem and also obtain balanced white emission spectra. Silica shells were then coated onto the doped QDs, allowing for the refractive index of the nanocomposites to be tailored while simultaneously improving their compatibility with the epoxy resin. The transparent doped ZnSe QD@SiO2/epoxy composite was then used as a light conversion and encapsulant material in combination with the near-UV-LED chip to fabricate the WLED. This fabricated WLED demonstrated high luminous efficiency and good color chromatics stability, suggesting that WLEDs based on highly fluorescent doped ZnSe QD@silica nanocomposites in combination with near-UV-LED chips may prove to be promising candidates for alternative light sources.

Mercaptopropionic acid-capped Mn(2+):ZnSe/ZnO quantum dots with both downconversion and upconversion emissions for bioimaging applications.

Doped quantum dots (d-dots) can serve as fluorescent biosensors and biolabels for biological applications. Our study describes a synthesis of mercaptopropionic acid (MPA)-capped Mn(2+):ZnSe/ZnO d-dots through a facile, cost-efficient hydrothermal route. The as-prepared water-soluble d-dots exhibit strong emission at ca. 580 nm, with a photoluminescence quantum yield (PLQY) as high as 31%, which is the highest value reported to date for such particles prepared via an aqueous route. They also exhibit upconversion emission when excited at 800 nm. With an overall diameter of around 6.7 nm, the d-dots could gain access to the cell nucleus without any surface decoration, demonstrating their promising broad applications as fluorescent labels.