• Bulletin of the Korean Chemical Society
• /
• v.22 no.9
• /
• pp.1005-1008
• /
• 2001

The lanthanide complexes have been anticipated to exhibit high efficiency along with a narrow emission spectrum. Photoluminescence for the lanthanide complex is characterized by a high efficiency since both singlet and triplet excitons are involve d in the luminescence process. However, the maximum external electroluminescence quantum efficiencies have exhibited values around 1% due to triplet-triplet annihilation at high current. Here, we proposed a new energy transfer mechanism to overcome triplet-triplet annihilation by the Eu complex doped into phosphorescent materials with triplet levels that were higher than singlet levels of the Eu complex. In order to show the feasibility of the proposed energy transfer mechanism and to obtain the optimal ligands and host material, we have calculated the effect depending on ligands as a factor that controls emission intensity in lanthanide complexes. The calculation shows that triplet state as well as singlet state of anion ligand affects on absorption efficiency indirectly.

• Bulletin of the Korean Chemical Society
• /
• v.17 no.11
• /
• pp.1000-1004
• /
• 1996

A random walk simulation was used to determine the triplet exciton density and annihilation rate for a two dimensional lattice of naphthalene choleic acid with small amount of β-methylnaphthalene (BMN). The results demonstrate that energy transfer efficiency (α) increases as density increases and the annihilation begins to become significant at triplet exciton densities higher then 10-3/sites. Another simulation was carried out to determine annihilation rate and unimolecular decay rate in the absence of BMN. The results indicate that the annihilation rate is equal to the unimolecular decay rate at the density of 1.2×10-3/sites.

• Korean Chemical Engineering Research
• /
• v.55 no.6
• /
• pp.731-744
• /
• 2017

Triplet-triplet annihilation upconversion (TTA-UC) is a special photochemical process that converts low energy photons to higher energy photon via combination of organic chemicals which fulfill specific energetic criteria. TTA-UC has been known as attractive technology that is able to enhance energy conversion efficiency of the photonic devices based on sunlight, which is achieved by conversion of wasted low energy photons in solar spectrum into higher energy photon. In the present paper, we introduced the photochemical mechanism and characteristics of TTA-UC phenomenon, which is yet unfamiliar to the domestic academia, and investigated recent research status, application, and future research directions of TTA-UC technology.

• Applied Chemistry for Engineering
• /
• v.30 no.1
• /
• pp.88-94
• /
• 2019

Triplet-triplet annihilation upconversion (TTA-UC) is a photochemical process wherein two or more low-energy photons are converted to a high-energy photon through a special energy transfer mechanism. Herein, we report a strategy to enhance the efficiency of TTA-UC through the light-scattering effect induced by silica microparticles (SM) embedded in polymeric thin films. By incorporating monodisperse uniform silica microparticles with a uniform size of 950 nm synthesized by $St{\ddot{o}}ber$-based seeded growth method into UC polymeric thin films, the UC intensity in the 430-570 nm range was enhanced by as much as 64% when irradiated by 635 nm laser. Analyzing the lifetime of PdTPBP phosphorescence revealed that the presence of SM in the UC layer does not affect triplet-triplet energy transfer (TTET) between sensitizers and acceptors, supporting the enhancement of TTA-UC originated from the light-scattering effect. On the other hand, the incorporation of SM in UC layer is shown to enhance the triplet-triplet annihilation (TTA) efficiency, which results in a 1.5-fold increase of the ${\Phi}_{UC}$, by scattering light source and thus increasing the number of excited photons to be utilized in TTA-UC process.

• Journal of Industrial and Engineering Chemistry
• /
• v.68
• /
• pp.350-354
• /
• 2018

Lifetime study of blue phosphorescent and thermally activated delayed fluorescent organic light-emitting diodes was carried out to understand the dominant degradation process during electrical operation of the devices. Doping concentration dependence of the phosphorescent and thermally activated delayed fluorescent organic light-emitting diodes was studied, which demonstrated long lifetime at low doping concentration in the phosphorescent devices and at high doping concentration in the thermally activated delayed fluorescent devices. Detailed mechanism study of the two devices described that triplet-triplet annihilation is the main degradation process of phosphorescent organic light-emitting diodes, whereas triplet-polaron annihilation is the key degradation factor of the thermally activated delayed fluorescent devices.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2005.07b
• /
• pp.1133-1137
• /
• 2005

In this paper, a renovated approach in the fabrication of red organic light-emitting diodes (OLEDs) is described. The hard-to-control doping process required for dopant-based red OLEDs can be avoided due to the novel red fluorophores that are not concentration quenching in solid state. Doping is in general a must for phosphorescence OLEDs because of the triplet-triplet annihilation, a common problem for phosphorophore dopants. However, we have recently found that extraordinary red iridium complex showing relatively short emission lifetime render the non-doped phosphorescence red OLED possible.

• Journal of Radiation Protection and Research
• /
• v.30 no.2
• /
• pp.85-89
• /
• 2005

Aspects of the scintillation mechanism in organic systems obtained on the base of precise measurements of the radioluminescence pulse shape are discussed. It shown that the process of scintillation light pulse formation is mainly determined by initial conditions of exited states generation.

• Applied Chemistry for Engineering
• /
• v.27 no.6
• /
• pp.639-645
• /
• 2016

We herein report efficient triplet-triplet annihilation upconversion (TTA-UC) achieved in various non-toxic and non-volatile vegetable oils as a UC media using platinum-octaethylporphyrin (PtOEP) and 9,10-diphenylanthracene (DPA) as a sensitizer and acceptor, respectively. Green-to-blue UC was readily achieved from PtOEP/DPA solution in vegetable oils with the quantum yield of 8% without any deoxygenation process. The UC efficiency was found to be significantly dependent on the contents of unsaturated hydrocarbon in vegetable oils and viscosity of the solution, as well. Though the Stern-volmer constant and quantum yield in vegetable oils were measured to be lower than those measured in the deaerated organic solvent, the quenching efficiency was still high enough to be 93%. In the sunflower oil, the UC threshold intensity ($I_{th}$) was approx. $100mW/cm^2$, which is far larger than the sunlight intensity, but we believe that the UC achieved in non-toxic and air-saturated media was still highly applicable to nontraditional visualization techniques such as bioimaging.

• Proceedings of the Polymer Society of Korea Conference
• /
• 2006.10a
• /
• pp.166-166
• /
• 2006

The photoluminescence (PL) efficiency of $Ir(ppy)_{3}$:PVK is lower than $Ir(ppy)_{3}$:CBP for the whole range of doping concentration and this low PL efficiency can be a reason of the lower efficiency of PhPLED than PhOLED. The lower efficiency is originated from the large bi-excitonic quenching such as the triplet-triplet annihilation. The PhPLEDs showed very short lifetime. The short lifetime was found to be originated from the instability of the doubly reduced $Ir(ppy)_{3^{-2}}$. The double reduction takes place because of the low electron mobility of PVK and large energy difference of LUMO level between PVK and $Ir(ppy)_{3}$.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2007.08b
• /
• pp.1474-1477
• /
• 2007

We demonstrate relaxation of roll-off characteristics by controlling the dopant concentrations and the thickness of an emitter layer in electrophosphorescence diodes composed of 2,6-dicarbazolo-1,5-pyridine (PYD2)-host doped with 25 wt%-Iridium(III)bis[(4,6-di-fluorophenyl)-pyridinato-$N,C^2$] picolinate (FIrpic).