Application of continuous wave and pulsed lasers in triplet−triplet annihilation upconversion (Invited)

The triplet−triplet annihilation upconversion is a new technology for photonic upconversion, which has the advantages such as continuous wave excitation, tunable upconversion wavelength and high upconversion quantum yields. In this upconversion process, as the energy donor, photosensitizer absorbs the light excitation, and intersystem crossing occurs, then sensitizes the energy acceptor through the triplet−triplet energy transfer process. Finally, the triplet−triplet annihilation of the energy acceptor in the triplet state generates a single excited state which can produce high−efficiency fluorescence (i.e. upconversion luminescence), thus the low−energy light is converted into higher−energy upconversion luminescence, which provides a feasible method for improving the photoelectric conversion efficiency of solar cells or the efficiency of photocatalysis, etc. It is desired to select appropriate lasers to excite the photosensitizer/energy donor system to study the steady upconversion luminescence and the upconversion kinetics. For instance, continuous wave diode pumped solid state laser (DPSSL) was selected as the light source to excite photosensitizer/acceptor system, upconversion luminescence was observed, and the effect of laser power density on upconversion luminescence can be studied conveniently. Additionally, in order to analyze the kinetic process of upconversion luminescence, with optical parametric oscillator (OPO) tunable pulsed laser as the light source, the lifetime of the triplet state, the kinetic characteristics of intermolecular energy transfer and triplet annihilation of photosensitizers can be studied. The application of continuous wave and pulse lasers in triplet–triplet annihilation upconversion experiments was introduced.