This presentation will report our recent studies on circularly polarized luminescence and persistent luminescence enabled by spin-orbital coupling and spin-phonon coupling effects. Our experimental studies of magnetic field effects found that the circularly polarized luminescence are essentially originated from the circularly polarized orbital ordering effects when spin-orbital coupling is combined with nonlinear optical polarizable structures. Furthermore, we found that extremely slow spin-phonon coupling can be realized by combining the un-usual phonon dynamics from dipolar crystalline structures with spin-orbital coupling. Interestingly, the extremely slow spin-phonon coupling can extend the excited state dynamics from traditional time window of nano/micro-seconds to an emerging time window of seconds, leading to persistent delayed fluorescence. Therefore, spin-orbital coupling and spin-phonon coupling function as an important mechanism to generate circularly polarized luminescence persistent luminescence.
Charge-transfer excitons are named as artificially engineered excitons carrying cooperatively mutually tunable energy, polarization, and spin-orbital coupling parameters that can be conveniently formed at heterostructured interfaces for wide-range optoelectronic applications. However, charge-transfer excitons have been remaining as an explored phenomenon in the new-generation semiconductors, namely solution-processing semiconducting perovskites, limiting the tuning abilities to control optoelectronic properties. Recently, we found that charge-transfer excitons can be conveniently formed as metastable states in both linear and nonlinear polarization regimes in quasi-2D and superlattice-2D heterostructured Pb/Sn perovskites. In linear polarization regime, charge-transfer excitons have led to broad light-emitting and photo-detecting capabilities with AC operating conditions in quasi-2D heterostructured perovskites [(PEA2PbI4)x:(PEA2SnI4)1-x]. In nonlinear polarization regime, charge-transfer excitons can enable normally-difficult-observed optical phenomena such as infrared-to-visible up-conversion luminescence and X-ray scintillation with self-amplified behaviors in superlattice-2D heterostructured perovskites [(PEA)2Pb1-x SnxI4]. Clearly, artificially-engineered charge-transfer excitons provide a new platform to further advance the optoelectronic properties in 2D perovskites. This presentation will discuss the key parameters of controlling charge-transfer excitons in quasi-2D and superlattice-2D heterostructured perovskites towards generating advanced light-emitting and photo-detecting properties in both linear and nonlinear polarization regimes.
Long-lived room temperature ‘phosphorescence’ from organic molecular crystals has attracted great attention owing to potential applications in organic electronics, information storage, and biotechnologies. The features of the persistent luminescence strongly depend on the electronic properties of the individual molecules, and on their molecular packing in the crystal lattice. Here, a new strategy is developed by rationally designing phosphors incorporating and combining for the first time a bridge for sigma-conjugation and a moiety for H-bond-directed supramolecular self-assembly. The molecular crystals exhibit room temperature ‘phosphorescence’ quantum yields that reach up to 20% and lifetimes up to 520 ms. This study provides a promising strategy for the development of molecular crystals exhibiting efficient long-lived room temperature persistent luminescence.
This presentation will present our recent studies on spin-orbital coupling (SOC) effects of light-emitting properties in organic and perovskite materials. In general, SOC generates two fundamental outcomes: (i) spin flipping in the absence of orbital momentum and (ii) Rashba effects in the existence of orbital momentum. The former and latter play a critical role in controlling light-emitting properties. In organic materials, this presentation will discuss the new mechanism of forming SOC from amorphous charge-transfer states in the absence of heavy-metal complex structures. Essentially, a charge-transfer state simultaneously possesses internally-interacting electrical dipole and spin dipole, providing the fundamental possibility to generate an electric-magnetic coupling phenomenon functioning as an artificially-formed SOC, towards realizing a thermally activated delayed fluorescence (TADF) in organic molecules. In perovskites, this presentation will discuss the orbit-orbit interaction
Long-lived room temperature phosphorescence from organic molecular crystals has attracted great attention owing to potential applications in organic electronics, information storage, and biotechnologies. The features of the persistent luminescence strongly depend on the electronic properties of the individual molecules, and on their molecular packing in the crystal lattice. Here, a new strategy is developed by rationally designing phosphors incorporating and combining for the first time a bridge for sigma-conjugation and a moiety for H-bond-directed supramolecular self-assembly. The molecular crystals exhibit room temperature phosphorescence quantum yields that reach up to 20% and lifetimes up to 520 ms. This study provides a promising strategy for the development of molecular crystals exhibiting efficient long-lived room temperature phosphorescence.
Our recent studies have found the unique phenomenon where the dissociation becomes a self-stimulated process occurring at donor:acceptor interfaces in non-fullerene organic solar cells [ITO/ZnO/C60-SAM/PM6:Y6/MoO3/Ag] with the remarkable power-conversion efficiency of 15.6 %. The self-stimulated dissociation was discovered by monitoring the dissociation at D:A (PM6:Y6) interfaces with our magneto-photocurrent measurement. It was observed that, as the excitons are increased, the dissociation at D:A interfaces becomes surprisingly easier, once the non-fullerene Y6 molecules are optically excited. This presents a self-stimulated dissociation where the electron-hole pairs experience an internal stimulation at D:A interfaces to dissociate into free carriers. This presentation will discuss the underlying mechanism of establishing self-stimulated dissociation in non-fullerene organic solar cells towards developing high-efficiency photovoltaics in non-fullerene organic solar cells.
In organic LEDs, converting dark states (triplets) into bright states (singlets) has become a crucial procedure to develop high efficiencies. Essentially, the triplet-to-singlet conversion requires a mechanism to flip the spins of triplets towards realizing the triplet-to-singlet conversion. Our recent studies have shown that charge-transfer states present a vital mechanism to generate a spin-orbital coupling (SOC) to flip spins towards converting triplets into singlets in exciplex systems. Furthermore, organic-inorganic halide perovskites are known as strong-orbital materials formed with bright (J = 1, named as triplets) and dark (J = 0, named as singlets) states. Our studies found that the orbit-orbit interaction between light-emitting states plays an important role to convert the dark states into bright states in hybrid perovskites. This presentation will discuss the SOC effects on light emission in organic and perovskite materials in spontaneous and stimulated regimes.
This presentation reports our recent studies on the understanding of spin-dependent processes in TADF (Thermally Activated Delayed Fluorescence) light-emitting materials based on magneto-optical studies. Recently, we have performed magneto-optical studies on TADF light-emitting molecules (DMAC-TRZ) by using magneto-photoluminescence (magneto-PL). Our magneto-PL studies provide the first evidence that the TADF is a spin-dependent process occurring in charge-transfer states. Essentially, the key spin-dependent process, namely spin mixing, necessarily required to activate the TADF, is determined by the competition between two critical parameters: (i) exchange interaction which functions as a resistance force to the TADF and (ii) spin-orbital coupling which acts as a driving force to the TADF. Therefore, controlling the exchange interaction and spin-orbital coupling becomes a critical issue in the development of highly efficient TADF light-emitting materials. By using magneto-PL studies, we further found that, doping soluble magnetic nanoparticles (surface-modified Fe3O4) can conveniently change the exchange interaction and spin-orbital coupling, and consequently alters the TADF rate. At low doping concentrations, the spin-orbital coupling is enhanced, leading to an increase on TADF rate. However, at high doping concentrations, the exchange interaction is increased, causing a decrease on the TADF rate. Furthermore, we studied the polarization effects of spin mixing in liquid TADF materials by using various solvents with different polarities. We observed that increasing the host polarization can directly weaken the spin mixing and leads to a decrease on the TADF rate. This experimental observation indicates that host polarization can weaken the spin-orbital coupling and thus decreases the driving force to TADF. Clearly, the magneto-PL studies provide an insightful understanding on the spin-dependent process to control the TADF rate in organic light-emitting materials.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.