The insets of Figure 5d are the bright-field optical and dark-field emission images of the nanobelt. A portion of the in situ emission propagated through the nanobelt and emitted at the opposite end, indicating that the nanobelt can act as an effective optical waveguide. Figure 5d is the corresponding far-field PL spectrum, which contains a near-band edge emission and a broad emission band between 525 and 725 nm. Similar
to the PL spectrum of nanobelt, the broad emission contains four bands: 541, 590, 637, and 689 nm (see the fitted red curve in Figure 5d). Therefore, the Mn2+ ion efficiently doped into the ZnSe matrix crystal with as dopant. Moreover, in contrast to the reported Mn2+ transition emission (see the PL of the nanobelt), the current Mn2+ emission band splits into many narrow sub-bands, that is, multi-mode emission. The PL mapping Selleckchem SAHA is carried out for individual sub-bands to explore the origin of the multi-mode emission and photon propagation process in the
nanobelt (Figure 5f). We can see that the near-band edge emission distributes in the whole nanobelt. In contrast, the mapping images of the Mn2+ ion emission sub-bands show irregular light intensity distribution along the nanobelt (the bright and dark regions represent find more the maximum and minimum intensities of emission, respectively). Moreover, there is slight modification between these Mn2+ ion emission mappings, such as it is a bright region at the end of 599 nm band, while it is dark for 637-nm band at the same position. This is due to the cavity mode selection within the belt. The mapping images indicate that there are several optical micro-cavities within the single nanobelt. Usually, the two end facets act as reflecting mirrors to form one Fabry-Pérot cavity in 1D nanostructures. However, multi-cavities can emerge in single doped 1D nanostructure
when a dopant with varied refractive indexes is incorporated into the matrix [13, 16]. In the HRTEM image (Figure 3f), we can clearly see some impurity and defect sites GNA12 possibly related to the Mn dopant in the nanobelt. When the nanobelt was excited, a large number of photons propagate along the axis, in which some were absorbed, some were AZD8931 cell line reflected or scattered by high refractive index domain, and some others passed through the segment boundary. These reflected photons propagate to another boundary and resonate at the boundary zones. So, different emission lines were selected to be observed in a single nanobelt. Combining the mapping images and multi-modes spectra, we can calculate the sub-cavity length L using the formula: Δ, where n is the refractive index (n = 2.67 for ZnSe), λ 1 and λ 2 are the resonant wavelengths, and Δλ is the mode spacing . The calculated cavity lengths of the adjacent bands are 9 to 11 μm, which are much shorter than the actual length of the nanobelt, but very close to the lengths of bright region in the mapping images.