Mazzaoui, Michel B, Canfield, Robert (2002). Turko-Persia in Historical Perspective. Cambridge University Press, "Islamic Culture and Literature in Iran and Central Asia in the early modern period", 86–7. ISBN 0521522919, ISBN 978-0-521-52291-5 "Safavid power with its distinctive Persian-Shi'i culture, however, remained a middle ground between its two mighty Turkish neighbors. The Safavid state, which lasted at least until 1722, was essentially a "Turkish" dynasty, with Azeri Turkish (Azerbaijan being the family's home base) as the language of the rulers and the court as well as the Qizilbash military establishment. Shah Ismail wrote poetry in Turkish. The administration nevertheless was Persian, and the Persian language was the vehicle of diplomatic correspondence (insha'), of belles-lettres (adab), and of history (tarikh)."
Savory, Roger (2007). Iran Under the Safavids. Cambridge University Press, pp. 213. ISBN 0521042518, ISBN 978-0-521-04251-2 "qizilbash normally spoke Azari brand of Turkish at court, as did the Safavid shahs themselves; lack of familiarity with the Persian language may have contributed to the decline from the pure classical standards of former times"
Encyclopædia Iranica:- "Safavid Dynasty Originating from a mystical order at the turn of the 14th century, the Safavids ruled Persia from 1501 to 1722."