Recently observed photoluminescence peak shifts toward higher energy in a longitudinal electric field in type-I Si1-xGexSi quantum wells and superlattices were attributed to a relatively large decrease of the exciton binding energy compared with quantum-confined Stark red shifts. However, careful investigation of the calculated and experimental results show that the observed blue shift can not be fully explained only with the reduction of exciton binding energy. The variational calculation adopted in the previous studies could not be justified for the moderate field strength regime, especially in the shallow quantum well. We suggest that the amounts of the shift calculated based on an Airy function approach can give a suitable account of the observed blue shift.