# Spin-Related Micro-Photoluminescence in Fe\({}^{3+}\) Doped ZnSe Nanoribbons
## 3 Results and Discussion
In Fe\({}^{3+}\) ion  
Figure 4: **(a)** temperature-dependent PL spectra of an individual Fe doped ZnSe nanoribbon from 5 to 300 K with 405 nm laser excitation; **(b)** the variation curves of intensity (I) (filled circles, filled triangles, and filled pentagons) and energy (E) (filled square) of emission peaks as a function of temperatures (T). The filled square shows the relationship between energy and temperature of near band edge and the filled circles, triangles, and pentagons curves correspond to intensity versus temperature of near band edge, D1 (filled triangles, 553 nm), and D2 (filled pentagons, 630 nm) emission peaks, respectively. doped ZnSe nanoribbons, Fe\({}^{3+}\) ion substitutes for the Zn\({}^{2+}\) site and introduces excess charges in ZnSe nanoribbons, resulting in the dominant BX and evenishing of EMP emission. Generally, the position of _d-d_ transition emission of TM ions in a crystal does not shift with temperature changing, while they change with temperature in Fe\({}^{3+}\) doped ZnSe nanostructure. This is because a high valence state Fe ion in a ZnSe lattice induces greater _p-d_ hybridization, and introduces more phonon scattering effect. It then modifies the energy of D1 and D2 _d-d_ emissions, as shown in Figure 4b. For heavy deep trap defects, this shift also scarcely happens. Hence, this phenomenon also demonstrates a difference from defect-related emission behavior [36]. The variation profiles of the emissions with temperatures increasing are plotted in Figure 4b. The energy variation trend of near band-edge emission with temperature is consistent with the Varshni function [38], as shown by the red line of Figure 4b. With increasing temperature, the intensities of near band-edge emission (black curve), D1 (blue curve), and D2 (green curve) emission decrease, which is due to the increasing of phonon scattering at high temperature and energy loss by thermal quenching [39]. The fast intensity reduction of near band-edge emission occurs because an exciton couples with an acoustic phonon and forms a bound exciton, which means that some Fe ions may be at the interstitial location. Interestingly, the intensity of the D1 emission peak increases firstly at low temperature (\(T<50\) K) and then starts to decrease with temperature increasing (\(T>50\) K). In the low temperature range, there is a thermal barrier or tunneling process that happens between the BX and the D1 state, which may be the valley potential well by Fe ions. There is another possibility coming from a ferromagnetic phase transition near 50 K, which needs further verification. In order to study the dynamic process of BX in Fe(III) doped ZnSe nanoribbon, PL lifetime measurements have been carried out. Figure 5a shows temperature-dependent normalized PL lifetimes of near band-edge emission of an individual Fe doped ZnSe nanoribbon from 5 to 300 K. The lifetime of near band-edge emission decreases with increasing temperatures when the temperature is lower than 60 K, and then has a fluctuation at a little range when the temperature is beyond 60 K. The temperature-dependent PL lifetimes fitted by a single exponential function were plotted in Figure 5b. The inset of Figure 5b shows the fitted results of PL lifetimes at 300 K. With the temperature increasing, the lifetime decreases from 1.1 to 0.67 ns, which is mostly due to the strong coupling between exciton and acoustic phonons. In particular, the lifetime has a sharp reduction when the temperature lowers than 60 K, which is different from that previously reported [40]. The magnetic phase transition in Fe doped ZnSe nanoribbon may be one cause. Figure 5: (**a**) temperature-dependent normalized PL lifetime measurement of near band-edge emission of an individual Fe doped ZnSe nanoribbon from 5 to 300 K with 405 nm femtosecond pulsed laser (duration: \(\sim\)130 fs, repetition rate: 76 MHz) as the excitation source; (**b**) plot of lifetime versus temperature.