Broad T emission band appears in the low-temperature spectra of β - ZnP 2 crystals between bands of the free excitons and biexcitons. This band is shown to be due to free ions of excitonic molecule (trions). The dependence of this band intensity I T on the excitation intensity I e x c (I T I e x c 3 / 2 ) proves trion origin of T band. The binding energy of trion has been determined as 4. 1 meV. Correlation of experimental intensities of the bands of trions and excitons is shown to be in good agreement with theoretical estimations. The behaviour of emission spectrum in external electric field has been studied. The intensity of T band decreases with increase of the applied voltage, proving the destroying of trions electric field.