We report on the impact of phosphorous ion-implantation-induced band gap tuning on the temperature dependent photoluminescence (PL) properties of InAs/InP quantum dashes (QDas). The high temperature range carriers' activation energy, extracted from Arrhenius plots, is found to decrease from 238 to 42 meV when the ion implantation dose increases from 10(11) cm(-2) to 5 x 10(14) cm(-2) which is consistent with the observed emission energy blueshift increase with increasing the ion implantation doses. This effect is attributed to the As/P exchange which reduces the carrier confining potential depth. For intermediate ion implantation doses the reduced carrier confining potential barrier combined with the non-uniform intermixing process, that causes an increased QDas size dispersion, result in anomalous temperature-dependent PL properties. Indeed, the temperature induced PL emission energy redshift measured between 10 K and 300 K is found to be strongly affected by the carrier redistribution within the broadened localized QDas states.