The phrase "a period of active" is correct and usable in written English.
It can be used to describe a specific timeframe during which something is happening or being engaged in actively.
Example: "During a period of active research, the team made significant breakthroughs in their study."
Alternatives: "a phase of engagement" or "a time of activity".
The reign of Catherine II was a period of active town planning and building.
The Early Miocene was a period of active rifting and carbonate platform development in the Midyan Peninsula, NW Saudi Arabia.
The basin is surrounded by Mercury's highest mountains towering 3 km (2 miles) above the plains and many lava vents, which point to a period of active volcanism.
They were beheaded owing to displacement of the Torreblanca and Irta faults during a period of active extensional faulting in Middle Pleistocene times.
President Lee C. Bollinger reveals the institution's new sustainability principles during a period of active discussion about whether the University should divest its endowment holdings in some or all fossil fuel companies.
On larger scales, approaching the size of the Galaxy itself, γ-ray observations have revealed the so-called 'Fermi bubble' features4, implying that our Galactic Centre has had a period of active energy release leading to the production of relativistic particles that now populate huge cavities on both sides of the Galactic plane.
The late 1970s was a period of more active negotiation on Arab-Israeli disputes.
Another great deposit-forming period occurred between about 2.8 and 2.65 billion years ago, when a large number of volcanogenic massive sulfide deposits formed; the probable cause of this metallogenic epoch was a period of extremely active submarine volcanism.
"Extended mission themes will include more comprehensive measurement of the magnetosphere and exosphere during a period of more active sun, greater focus on observations at low spacecraft altitudes and a greater variety of targeted observations.
"It's definitely a period of very active brain growth that if you disrupt in the wrong way could easily could have some important implications".
This is followed by a period of highly active growth with abundant filopodia formation.
