This thesis decay rate enhancement and photophysics of nitrogen vacancy (NV) centers in diamond and quantum emitters in hexagonal boron nitride (hBN). The NV center in diamond is a unique physical system that ﬁnds use in many quantum technologies such as quantum sensing, quantum information processing and single photon generation. Consisting of a substitutional nitrogen atom next to a vacant lattice site, the NV center introduces discrete electronic energy levels within the wide bandgap of diamond. The NV center can be optically excited and will emit single photons upon relaxation that hold information of the spin state of the NV center. In this thesis, we use metallic structures to modify and enhance the decay rate of NV centers in bulk and nano diamonds in three diﬀerent experiments. Such an enhancement is a way to improve the usability of NV as a single photon source. Using TiN ﬁlms with metamaterial properties we observe a 2-fold decrease of the total excited state lifetime of NV centers in nano diamonds, when comparing to similar NV centers not inﬂuenced by the TiN ﬁlms. For shallow implanted NV centers in bulk diamond we experimentally investigate how a decay rate enhancement inﬂuences the signal-to-noise ratio (SNR) in spin readout measurements. In this experiment we perform spin state readout before and after introducing a rate enhancement and ﬁnd a 30 % drop in spin contrast. We model the spin readout measurements using a ﬁve-level model and use that to predict the SNR under higher rate enhancement. In the last NV related experiment we use a curved metallic mirror on top of shallow implanted NV centers, to measure the continuous lifetime modiﬁcation as a function of distances to the mirror. This allows us to determine the internal quantum eﬃciency (IQE) by ﬁtting the experimental data with a model that includes calculating the expected Purcell factor. We ﬁnd IQE values of 0.70±0.07 and 0.82±0.08 for implantation depths of 4.5±1 and 8±2 nm, respectively. Last but not least, newly discovered bright single photon emitters in two dimensional hBN were investigated. Similar to the NV center they are believed to be crystal defects, but the defect conﬁguration is not fully known. In this thesis, the photophysics of quantum emitters in hBN nano ﬂakes are investigated. Intensity autocorrelation measurements indicate the presence of at least two metastable states, seen by distinct photon bunching levels on long time scales in the g(2)(τ)-functions. We also observe blinking behaviour, which we show can be explained by changes in the IQE. From rate equation ﬁtting we ﬁnd that transition rates scale linearly with excitation power. Based on the transition rates we estimate the IQE to be close to unity for excitation powers below saturation.