Interplay between Amplified Spontaneous Emission, Förster Resonant Energy Transfer, and Self-Absorption in Hybrid Poly(9,9-dioctylfluorene)-CdSe/ZnS Nanocrystal Thin Films

Abstract

We investigated the excitation density dependence of the photoluminescence spectra of hybrid poly(9,9-dioctylfluorene)-CdSe/ZnS nanocrystals (PF8-NCs) thin films. We demonstrate that this experiment allows the determination of the efficiency of all the CdSe/ZnS NCs excitation processes and that the presence of amplified spontaneous emission (ASE) from the PF8 leads to a strong dependence of the NC excitation processes from the laser excitation density. Below the PF8 ASE threshold only about 6% of the excitons in the NCs are due to pump laser absorption, while about 94% of the NC excitation is due to the interaction with the PF8, and it is due for about 58% to PF8-->NC Forster resonant energy transfer (FRET) and for about 37% to reabsorption by the NCs of the PF8 luminescence. The presence of PF8 ASE significantly modifies this scenario by strongly decreasing the FRET importance and strongly increasing the reabsorption one. The interplay between reduced FRET and increased reabsorption overall decreases the NC excitation due to PF8 indicating that ASE from the donors should be avoided if efficient NCs excitation under strong pumping is wished.

Excitation Density Dependence of Optical Oxygen Sensing in Poly(9,9-dioctylfluorene) Waveguides Showing Amplified Spontaneous Emission

“…Our results are ascribed to oxygen induced reversible quenching, in agreement with previous results [6] on optical oxygen sensing exploiting PF8 SE, and with similar results on ASE quenching [9,10]. In order to quantitatively investigate the intensity quenching of SE and ASE and their excitation density dependence we determined the emission intensities in vacuum ( vac ) and in air ( air ), by integrating the spectra in the range 410-430 nm for SE and 441-449 nm for ASE.…”

“…Among the different proposed techniques, exploiting the oxygen effects on the electric conductivity [2], material color [3], and chemiluminescence [4], optical sensors, based on the oxygen induced photoluminescence quenching, are characterized by fast response time and high sensitivity. The typical active systems are blends between an inert matrix and a phosphorescent molecule [5], while reversible oxygen induced fluorescent quenching in poly(9,9-dioctylfluorene) (PF8) neat films was recently demonstrated [6]. A recent breakthrough in the sensitivity enhancement was represented by the demonstration that in neat active films showing optical gain, the Amplified Spontaneous Emission (ASE) and the laser intensity show a stronger relative quenching with respect to the Spontaneous Emission (SE) [7], exploited in efficient explosive vapours detection.…”

Multiband Laser Action from Organic-Organic Heteroepitaxial Nanofibers

“…Shortening of p6P PL lifetime induces a progressive modification of the 6T emission transient, whose rise time become faster and faster till it becomes resolution limited (right panel). The excitation density dependence of resonance-energy transfer in donor-acceptor systems when the donor has stimulated emission has been investigated few years ago in organic-inorganic blends [11]. Competition between p6P-to-6T RET and p6P lasing results in saturation of the 6T emission intensity above p6P lasing threshold.…”

Mn2+-activated calcium fluoride nanoprobes for time-resolved photoluminescence biosensing

“…The broad emission band of Mn 2+ enhances spectral overlap with the excitation band of the energy acceptor, resulting in an enhanced FRET efficiency [25][26][27][28]. Nonetheless, the reabsorption process, which is unavoidable in homogeneous luminescent bioassays, may interfere with the FRET signal and lead to incorrect detection results [29][30][31]. Therefore, it is of fundamental importance to gain deep insights into the energy transfer process and establish a reliable method for Mn 2+ in homogeneous TR-FRET biodetection.…”