A long-term stable photoactive composition, namely a phosphorescent composition or a TTA-photon upconversion composition, contains: a) at least one compound, which has a triplet state capable of energy transfer via an emissive process or a non-emissive process, wherein the at least one compound having a triplet state is i) at least one phosphorescent compound and/or ii) at least one sensitizer compound being capable of absorbing radiation at a first frequency v1 and at least one emissive compound, wherein the at least one sensitizer compound is capable of transferring energy to the at least one emissive compound and wherein the at least one emissive compound, after obtaining energy transferred from the at least one sensitizer compound, is capable of emitting light at a second frequency v2, wherein the following equation is fulfilled: v2>v1, wherein the at least one sensitizer compound is capable of a triplet-triplet energy transfer to the at least one emissive compound and wherein the at least one emissive compound is preferably capable of a triplet-triplet annihilation, and b) at least one compound capable of reacting with singlet oxygen, wherein the at least one compound capable of reacting with singlet oxygen comprises at least one terminal unsaturated carbon-carbon bond and is selected from the group consisting of compounds having anyone of the general formulae (I) to (X).