The photoluminescence (PL) spectra and UV-Visible absorption spectra of a novel yellow phosphor dye of bis［2-(4-tert-butylphenyl)benzothiazolato-N,C2′］ iridium (acetylacetonate) denoted as (t-bt)2Ir(acac) were systematically investigated, which were measured in solution and film states with various concentrations. The results showed that the highest PL intensity was achieved when the solution concentration was 3×10－4 mol·L-1, and it decreased dramatically when the concentration kept on increasing because of concentration quenching of the phosphor dye. A red shift for PL spectra and UV-Vis absorption spectra of films compared to those of solutions were found, which is due to the shorter distance, aggregation effect, and stronger interaction of dye molecules in solid state. Based on the spectrum characterization, organic light-emitting diode was fabricated with an ultrathin structure based on this phosphor dye, which showed a high luminescence of 18 367 cd·m-2 at a bias of 13.2 V.