Intersystem-crossing and excited-state absorption in eosin Y solutions determined by picosecond double pulse transient absorption measurements

Abstract

The transmission measurement of two intense picosecond pulses (wavelength A t = 527 nm) separated by 10 ns is applied to extract the quantum yield of triplet formation <£ T , the S l singlet excited state absorption cross-section <r cx , the T, triplet absorption cross-section cr T

Triplet-triplet absorption of eosin Y in methanol determined by nanosecond excimer laser excitation and picosecond light continuum probing

“…a em ( I^SE ) and <r cx ( I>ASE ) are the stimulated emission cross section and the excitedstate absorption cross section at the amplified spontaneous emission frequency ^ASE (position of maximum gain), respectively. For our experimental situation (^=0.44 [57], yv 0 =2xl0 16 Along the pump pulse duration, N y increases initially with the rise of the temporal Gaussian pump pulse intensity and then declines to zero due to intersystem crossing to the triplet system and relaxation to the singlet ground state. In our experiments the amplified spontaneous emission practically does not reduce the triplet level population and therefore does not influence the triplet-triplet absorption cross-section measurement.…”

“…The population number densities of the levels / are denoted by N h The relaxation time constants [56] and T t [57] are very short (subpicosecond range) compared to the pump pulse duration (A/ L « 10 ns). Therefore the level population number densities N 2 (t\ z'), N A (t\ z'), and N 6 (t\ z') remain approximately zero over all times and do not appear in the above equation system (l)-(4).…”

Singlet excited-state absorption of eosin Y

“…The optical delay line DL in the probe pulse branch is adjusted to an optical delay of r d % 30 ps of the probe pulse behind the pump pulse. This delay time is short compared to the fluorescence lifetime, and intersystem crossing to a triplet state is negligible for this short time delay [32] The dye eosin Y in methanol is investigated at room temperature. Eosin Y was purchased from Heraeus and was purified by recrystallization six times from ethanol.…”

“…o*xX(Q)=^CX,L is used in the equations (for a discussion see ref. [32]). The generated angularly anisotropic level populations N t {0) relax to isotropic distributions N t with the molecular reorientation time r or .…”

“…The pump pulse absorption dynamics determines the S r state level population as a function of time, and the probe pulse transmission allows the determination of excited-state absorption as a function of wavelength. In a previous paper on intersystem crossing [32] a differential equation system for the level populations and the light pulse propagations was given. Here, in the following equation system triplet level population is neglected (delay time of probe pulse is short compared to inverse intersystem crossing rate) and amplified spontaneous emission is not included since it is negligible for our experimental conditions (see below).…”