Single atoms or solid-state emitters are very promising candidates for building quantum network nodes as they provide for a spin-photon interface that also has quantum information processing capabilities. Among solid-state materials, rare earth ion-doped crystals constitute a promising platform for quantum information processing and networking. They feature exceptional spin coherence time to store information, narrow optical transitions to act as an interface to optical photons (including at telecom wavelength for erbium ions), and possibilities to realize quantum gates between single ion qubits. Coupling quantum emitters to optical cavities enables channelling the emission from the emitters into the cavity mode while decreasing their emission lifetime. This allows the realization of an efficient and high-rate spin-photon interface, while also increasing the indistinguishability of the emitted photons in the presence of dephasing. However, a reduction in the excited state lifetime also reduces the time available to realize quantum gates that rely on a dipole-blockade mechanism achieved by driving the emitter to the excited state. Dynamic control of the Purcell factor would hence enable decoupling the emitter from the cavity when performing gates, and coupling it back at a desired time to emit a single-photon with a tunable waveshape. In this work [1], by utilizing erbium-doped nanoparticles coupled to a fully tunable high-finesse fiber-based optical cryogenic microcavity, we demonstrate a Purcell factor of 31 that can be controlled on a timescale of 100 microseconds, which is more than 100 times faster than the spontaneous emission lifetime of the erbium ions. This is achieved by tuning the length of the cavity, and hence its resonance frequency, via a piezoelectric device with sub-nanometre precision. Additionally, we demonstrate that this technique can be operated with a bandwidth high enough to shape deterministically the spontaneous emission of the erbium ions. With some improvements, this technique has the potential to reach switching times of a few microseconds. Combined with single-ion addressing, this ability will enable the generation of fully tunable narrowband single photons at telecom wavelengths, and quantum processing using single rare-earth-ions. Our approach therefore opens the door to a solid-state quantum node with the potential of exhibiting quantum computing and communication capabilities all in a single device. [1] Bernardo Casabone, Chetan Deshmukh, Shuping Liu, Diana Serrano, Alban Ferrier, Thomas Hümmer, Philippe Goldner, David Hunger, and Hugues de Riedmatten, “Dynamic control of Purcell enhanced emission of erbium ions in nanoparticles”, arXiv:2001.08532 (2020)