Ah. Bougourzi et L. Vinet, ON THE RELATION BETWEEN U-Q(SL(2)) VERTEX OPERATORS AND Q-ZONAL FUNCTIONS, letters in mathematical physics, 39(4), 1997, pp. 299-311
We show how the states constructed from the action of the modes of bos
onized vertex operators that intertwine U-q <((sl(2)))over cap> module
s are related to q-zonal functions.