The slow decrease of the fluorescence intensity at later times is caused, in addition to other processes, by non-photochemical quenching.
ðə slˈoʊ dˈiːkɹiːs ʌvðə flʊɹɹˈɛsəns ɪntˈɛnsᵻɾi æt lˈeɪɾɚ tˈaɪmz ɪz kˈɔːzd, ɪn ɐdˈɪʃən tʊ ˈʌðɚ pɹˈɑːsɛsᵻz, baɪ nˈɑːnfˌoʊɾoʊkˈɛmɪkəl kwˈɛntʃɪŋ.