The quantum theory of light reveals a counter-intuitive result for the existence of the lowest energy state of quantized light, the quantum vacuum state. According to quantum theory, the vacuum electromagnetic field that fills arbitrary spaces accounts for radiative transitions in condensed matter through carrier-photon interaction. With precisely designed nano-structures, it is possible to manipulate the local distribution of vacuum electromagnetic field in confined spaces. For instance, the Spontaneous Emission (SE) rate can be statically modified by shaping the vacuum field at the position of the nano-emitter when it is inside a micro-/nano-cavity or nearby a plasmonic structure. The typical experimental signature is either an inhibition or acceleration in SE rate.So far vacuum field and hence the SE rate at nano-scale is generally determined by the electromagnetic design. The enhancement or inhibition ratio of the SE rate is usually fixed after the device fabrication, while real-time(post-fabrication) manipulation of vacuum field brings in an additional tunability for Cavity Quantum Electrodynamics (CQED) studies. This paves the way for developing various applications in classical and quantum photonics that are otherwise impossible. Recently, dynamically tunable active devices based on semiconductor materials have been intensively investigated. This kind of dynamic or quasi-dynamic approach leads to a series of new nanophotonic device concepts and may find its applications in quantum light sources and micro-/nano-cavity lasers.This review focuses primarily on controlling radiative processes through post-fabrication manipulation of the vacuum electromagnetic field. Semiconductor optical microcavities, known for their ability to trap photons and prolong their lifetimes within the cavity, play a vital role in enhancing light-matter interactions by precisely manipulating the photon density of states, which are crucial for fundamental radiation processes such as spontaneous and stimulated emission.This review is organized as follows.: the first section outlines the fundamental theory of radiative processes within the framework of CQED, including detailed discussions on light-matter interactions and derivations of the local density of states and the Purcell factor for arbitrary inhomogeneous dielectrics. Efforts to minimize the mode volume of optical microcavity for an enhanced emission are discussed and further illustrated with a review on various micro- and nano-cavities including self-assembled quantum dots in photonic crystal (PhC) cavities. The second section focuses on SE in single or coupled cavities, especially within PhC cavities, summarizing three methods to dynamically manipulate the coupling effects of the emitter and devices to control their radiative processes. These include altering the refractive index distribution of semiconductor materials, dynamically controlling external environmental parameters of the emitters and micro-/nano-cavities, and real-time adjustment of coupling effects in these cavities. The review also details the implementation of cavity-emitter detuning variations in the PhC platform, enabling modulation of the SE rate of a quantum dot within a single photonic crystal cavity, and discusses manipulation of vacuum-field properties in two (or more) coupled cavities using external fields such as light, thermal, electrical, magnetic, and mechanical force fields. The last section discusses methods developed for controlling stimulated emission, emphasizing control methods involving field distribution in spatial pumping, coupled cavities, and complex physical mechanisms like parity-time symmetry.This review concludes with an outlook on future prospects of functional nanophotonic devices. We offer a brief outlook on future directions. The development of micro- / nano-photonic devices may focus on three areas: uncovering more complex physical mechanisms through innovative vacuum field control to enable advanced light-matter interactions; adopting more flexible control methods that allow independent manipulation of devices' temporal and spatial characteristics; and designing practical devices. These advancements are crucial for dynamically controlling device performance and integrating them into photonic chips and quantum information networks.