The electronic structure and geometric distribution of neutral and charged states of interstitial O in potassium dihydrogen phosphate were investigated by using a first-principles method. The energy gap was lowered to about 4.2eV from the density-functional theory value of 5.9eV by a neutral O interstitial, which corresponded to a 2-photon absorption of 364nm (3.4eV) after correction of 1.3eV due to the under-estimation of the band-gap using density-functional theory. The addition of a single electron narrowed the gap to 1.4eV. The addition of 2 electrons led to the formation of an isolated interstitial H2O molecule in potassium dihydrogen phosphate, accompanied by the breaking of two H-bonded chains, and thus no defect states appeared in the energy gap. The results were used to explain a recently reported decomposition of potassium dihydrogen phosphate during laser-induced breakdown.

First-Principles Study of Interstitial Oxygen in Potassium Dihydrogen Phosphate Crystals. K.Wang, C.Fang, J.Zhang, C.S.Liu, R.I.Boughton, S.Wang, X.Zhao: Physical Review B, 2005, 72[18], 184105 (5pp)