**2.4 Template-assisted method**

In this synthesis approach, NP formation is induced by a specific substrate such as mesoporous silica and aluminum oxide film as a template [36–38]. NPSs is obtained on the films which exhibits intensive light. This technique is suitable for formation of mono disperse NPSs with various narrow emissions (full wind of half maximum (FWHM) is less than 40 nm) bands from green (FWHM: 22 nm) to near infrared (FWHM: 36 nm) by template optimization [37–39]. In a recent study, perovskite nanocrystals have been prepared in a nano-porous structure. By this kind of strategies, it is possible to confine PNSs (<10 nm) without any capping agents (**Figure 4**). In other words, the emission wavelength of perovskite nanoparticles can be arranged precisely for sophisticated photonic applications such as lasers [36, 37].
