of about 5.3 meV which shows a good agreement to the ambient thermal energy at 70 K. Traditionally, ZnO:Zn with high defect emission can be created directly through the use of very high temperature processes. We have shown here that through the sulfurization/desulfurization process strong defect emission can be induced at lower temperatures with greater control over degree of defects induced. This is an important advancement, particularly in the field of earth-abundant phosphors. Experimental Details and Analysis Method ZnO nanowires were prepared by chemical bath deposition on quartz and silicon substrates. 0.035 M Zinc acetate was dissolved in 750 mL of DI water. 9 ml of ammonium hydroxide was added to this solution. The ZnO seed layer pre-coated quartz and silicon substrates were immersed in this solution for one hour at 87 °C (details of the deposition technique have been reported elsewhere 28). The desulfurized ZnO was prepared via two steps, namely sulfurization and desulfurization, in a chemical vapor deposition (CVD) reactor (a horizontal tube furnace).

We report an in-depth analysis of ZnO micropods emission. A strong correlation between defect and interband emissions is observed. ZnO micropods were grown using low-temperature chemical bath deposition (CBD). ZnO micropods exhibited perfectly-crystalline hexagonally-shaped facets with various numbers of branches. Raman studies showed that ZnO micropods contained trapped zinc hydroxide (OH) and imidogen (NH) defects that originate from the precursor solution used in the CBD technique. These defects were evacuated by thermal annealing, leading to the recrystallization in the volume of the micropods and the formation of structural defects at their surface, as attested by scanning electron microscopy and X-ray diffraction. More importantly, the thermal annealing was accompanied by a breakdown of the NH defects, which resulted in a nitrogen doping of the ZnO micropods. The structural changes as well as the nitrogen doping resulted in a drastic change in the photoluminescence (PL) spectrum of the ZnO micropods that exhibited a stronger free exciton UV emission as well as a stronger visible (white) emission. An in-depth low-temperature PL study of both UV and visible emission reveals a strong interplay between the structural-defect bound excitonic UV emission (Y-band) and the deep donor (visible) emission, which suggests a rather complex emission mechanism involving an efficient nonradiative energy transfer between the Y-band states and defect states leading to the enhanced visible emission of ZnO micropods after high temperature annealing.

The ability to correlate optical hyperspectral mapping and high resolution topographic imaging is critically important to gain deep insight into the structure–function relationship of nanomaterial systems. Scanning near-field optical microscopy can achieve this goal, but at the cost of significant effort in probe fabrication and experimental expertise. To overcome these two limitations, we have developed a low-cost and high-throughput nanoimprinting technique to integrate a sharp pyramid structure on the end facet of a single-mode fiber that can be scanned with a simple tuning-fork technique. The nanoimprinted pyramid has two main features: (1) a large taper angle (∼70°), which determines the far-field confinement at the tip, resulting in a spatial resolution of 275 nm, an effective numerical aperture of 1.06, and (2) a sharp apex with a radius of curvature of ∼20 nm, which enables high resolution topographic imaging. Optical performance is demonstrated through evanescent field distribution mapping of a plasmonic nanogroove sample, followed by hyperspectral photoluminescence mapping of nanocrystals using a fiber-in-fiber-out light coupling mode. Through comparative photoluminescence mapping on 2D monolayers, we also show a threefold improvement in spatial resolution over chemically etched fibers. These results show that the bare nanoimprinted near-field probes provide simple access to spectromicroscopy correlated with high resolution topographic mapping and have the potential to advance reproducible fiber-tip-based scanning near-field microscopy.