The stability of photoluminescent intensity from Y3Al5O12: Ce (YAG), Y2O2S: Eu (YOS), ZnS: CuAl (ZnS), and (Sr0.98Ba0.02)(2)SiO4: Eu (SBS) phosphors under UV irradiation in air are reported. For exposure to 325 nm irradiation at a flux of 5.4 x 10(22) photons/cm(2)-s the orthosilicate SBS phosphor was the most stable. Specifically, after irradiation for 2 h at 5.4 x 10(22) photons/m(2)- s (3.31 x 10(4) W/m(2)), the relative intensity was reduced to 84%, 92% (1 h irradiation), 88%, and 91% of the maximum for YAG, ZnS, YOS, and SBS, respectively. In general for YAG, YOS, and SBS, the relative intensity decreased monotonically with time. In contrast, the relative intensity of ZnS initially increased, reached a maximum after,1000 s and then decreased to a value of 92% of maximum after 1 h of exposure to 325 nm irradiation in air. Photon-stimulated surface chemical reactions are discussed as possible mechanisms for these changes. (C) 2005 The Electrochemical Society.