Abstract
The spin–orbit coupling mechanism was generally used to explain heavy atom effect induced room-temperature phosphorescence (RTP). Here, we demonstrate that the mechanism of RTP induced by Gd3+ from hematoporphyrin monomethyl ether (HMME) is due to the mixing of singlet (S) and triplet (T) states. The spin-forbidden transition between S and T states was partly allowed due to the states mixing, as indicated by the direct absorption corresponding to transition from S0 to T1, which was observed for the first time from RTP. The quantum yield of T1 was determined to be 0.80, and the percent of each energy transfer process was determined. Meanwhile there is no nonradiative relaxation from HMME to Gd3+ because of the large energy gap between the excited and ground states of Gd3+. The special energy level of Gd3+ as well as the states mixing between S and T states produced the strong phosphorescence emission. The population and deactivation of triplet states in heavy atom induced RTP can be used to analyze the mechanism of phosphorescent emission.
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