Banca de DEFESA: LETÍCIA FERREIRA MAGALHÃES

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : LETÍCIA FERREIRA MAGALHÃES
DATE: 05/08/2022
TIME: 14:00
LOCAL: On-line
TITLE:

Study of Photophysical Processes Resulting from the Interaction between CsPbBr3 Perovskite Nanocrystals and Rhodamine 6G Dye

KEY WORDS:

Perovskites, FRET, Energy Transfer, Dexter, Rhodamine 6G. 

PAGES: 3064
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Química Inorgânica
SPECIALTY: Físico Química Inorgânica
SUMMARY:

Lead halide perovskites nanocrystals (NCs) have emerged as attractive light-harvesting and emitting materials for many applications. These NCs are characterized to have a broad absorption spectrum with a high absorption coefficient (>10⁵M^-1 cm^-1). Nevertheless, the radiative lifetime of these NCs is a few nanoseconds at room temperature, which can limit their application in charge- and energy-transfer-related applications. To obtain a high absorption coefficient and a long-lived excited state, triplet energy transfer (TET) to organic molecules has been developed as an effective means to store the excitation energy of NCs in long-lived molecular triplets. In the past 5 years, different approaches have been used for triplet sensitization of organic molecules via Dexter mechanism, but it requires that the acceptor triplet state-level lies at lower potentials than the conduction band level of the NCs. Moreover, this mechanism is only efficient for short distances (<1 nm). On the other hand, FRET is still efficient for longer distances such as (2 to 10 nm), but it requires a large spectral overlap between the absorption and emission spectra of acceptors and donors. For triplet sensitization, FRET is inefficient because triplet absorption is dipole forbidden. Since R6G dimers have singlet and triplet energy states close to each other, favoring intersystem crossing, we can take advantage of the large spectral overlapping between the emission of CsPbBr₃NCs and the singlet-state absorption of R6G dimers to access their triplet-state via FRET. Here, we synthesized colloidal dispersions of CsPbBr₃ perovskite NCs with a cubic shape and mean size of 10 nm. While the dimers of R6G were prepared by a very high concentrated solution of R6G in ethanol followed by a successive dilution of it into toluene. The dimers were characterized by their steady-state absorption spectrum with a band centered at 511 nm, which is well documented in the literature and typical of H-aggregates. We also observed the dimer emission band centered at 620 nm employing time-resolved photoluminescence (TR-PL), with a lifetime of 600 ps. Such a fast lifetime is due to the efficient intersystem crossing of the dimer. The emission of the NCs and absorption spectra of the dimers are very well overlapped, with a critical distance (R₀) of 5.5 nm, according to FRET formalism. When we mixture the colloidal dispersion of NCs with the R6G dimers, we observed that the dimers effectively quench the photoluminescence of the NCs, increasing the emission intensity of the dimer.  TR-PL also indicates that the quenching involved is dynamic and occurs by FRET. Therefore, after excitation, CsPbBr₃ NCs transfer their energy via FRET to the singlet excited state of R6G dimers, relaxing quickly to the triplet state. We probed the triplet state of the R6G dimers using µs-transient absorption spectroscopy.

BANKING MEMBERS:
Interno - 1527524 - WAGNER SOUZA MACHADO
Interno - 1443844 - MARCO ANTONIO SCHIAVON
Externo à Instituição - FERNANDO APARECIDO SIGOLI - UNICAMP
Externo à Instituição - BRENER RODRIGO DE CARVALHO VALE - UNICAMP