Low Power Visible-to-UV Upconversion

Abstract

Low power visible-to-UV photon upconversion is demonstrated for the first time, achieved from two simple organic chromophores dissolved in benzene. Selective 442 nm excitation of the triplet sensitizer 2,3-butanedione (biacetyl) in the presence of the laser dye 2,5-diphenyloxazole (PPO) results in the observation of singlet fluorescence from the latter in the UV centered at 360 nm, anti-Stokes shifted by a record 0.64 eV with respect to the excitation. All of the experimental data are consistent with the upconverted singlet PPO fluorescence being produced as a result of biacetyl-sensitized triplet-triplet annihilation (TTA) of triplet excited PPO chromophores. Nanosecond laser flash photolysis performed under pseudo-first-order conditions revealed the bimolecular rate constant of triplet-triplet energy transfer between the biacetyl sensitizer and PPO acceptor, k(q) = 9.0 x 10(8) M(-1)s(-1). The TTA process was confirmed by the quadratic dependence of the upconverted integrated PPO emission intensity measured with respect to incident 442 nm light power density. The maximum quantum yield of the upconverted emission (0.0058 +/- 0.0002) was determined relative to 1,8-diphenyl-1,3,5,7-octatetraene, both measured with 0.389 W/cm(2) incident power density. The PPO triplet-triplet annihilation rate constant (k(TT)) was determined from transient absorption decays monitored at the peak of its characteristic triplet-to-triplet excited-state absorption (500 nm) as a function of incident pulsed laser fluence; this process attains the diffusion limit in benzene at room temperature, k(TT) = 1.1 +/- 0.1 x 10(10) M(-1) s(-1).

Visible‐Light‐Harvesting Triphenylamine Ethynyl C60‐BODIPY Dyads as Heavy‐Atom‐Free Organic Triplet Photosensitizers for Triplet‐Triplet Annihilation Upconversion

“…[10][11][12][13][14][15][16][17][18] In this kind of upconversion, a triplet photosensitizer and a triplet acceptor are combined for implementation of the cascade photophysical processes. The photosensitizer is responsible for light-harvesting, and after population of the triplet excited state of the sensitizer by intersystem crossing (ISC), the excited energy is transferred to the triplet acceptor by triplet-triplet energy transfer (TTET).…”

“…The radiative decay of the acceptor from the singlet excited state will produce upconverted fluorescence (see Figure 7 below). [10][11][12][13][14][15][16][17][18] The triplet photosensitizers are usually transition-metal complexes, such as Pt II /Pd II porphyrin complexes, Ir III complexes, or Ru II complexes, because ISC is facilitated by the heavy-atom effect. [11,12] The triplet acceptors are usually polycyclic aromatic hydrocarbons, such as 9,10-diphenylanthracene or perylene.…”

“…[15, 17a-c] The heavy-atom-free organic triplet photosensitizer 2,3-butanedione has been used for TTA upconversion. [18] However, this organic triplet photosensitizer absorbs in the UV/ blue range and the absorption is weak. Heavy-atom-free organic triplet photosensitizers with absorption in visible range are highly desired for TTA upconversion.…”

Transition-Metal Complexes for Triplet–Triplet Annihilation-Based Energy Upconversion

“…The intersystem crossing rate constant is extremely fast (ca.10 10 sec À1 ) in some aromatic carbonyls whose lowest singlet is an n,π* state below which there is a triplet π,π* state, according to El-Sayed rule [87]. The transition of S n,π* to T π,π* is allowed in these organic molecules, such as OS-15 [88], OS-16 [89], and OS-17~OS-19 [90], and these compounds can be used as triplet sensitizers in TTA-based upconversion. …”

Er3+/Yb3+ upconverters for InGaP solar cells under concentrated broadband illumination

“…Such concentrated photovoltaic (CPV) systems generally are also equipped with type III-V solar cells. At variance with most research on the subject of enhancing solar cell performance using lanthanide upconverters, 3,4,9,16,18,[20][21][22][23][24][25][26][27] the current study focuses on the use of broadband illumination utilizing a flash light set-up instead of laser excitation at specific wavelengths. This is done to more closely approach the conditions under which the system should perform in any practical application.…”