  Two-dimensional van der Waals materials have emerged as promising platforms
for solid-state quantum information processing devices with unusual potential
for heterogeneous assembly. Recently, bright and photostable single photon
emitters were reported from atomic defects in layered hexagonal boron nitride
(hBN), but controlling inhomogeneous spectral distribution and reducing
multi-photon emission presented open challenges. Here, we demonstrate that
strain control allows spectral tunability of hBN single photon emitters over 6
meV, and material processing sharply improves the single-photon purity. We
report high single photon count rates exceeding 10^7 counts/sec at saturation,
which is the highest single photon detection rate for room-temperature single
photon emitters, to our knowledge. Furthermore, these emitters are stable to
material transfer to other substrates. High-purity and photostable single
photon emission at room temperature, together with spectral tunability and
transferability, opens the door to scalable integration of high-quality quantum
emitters in photonic quantum technologies.
