Best practice in determining key photophysical parameters in triplet–triplet annihilation photon upconversion

Abstract

Triplet–triplet annihilation photon upconversion (TTA-UC) is a process in which low-energy light is transformed into light of higher energy. During the last two decades, it has gained increasing attention due to its potential in, e.g., biological applications and solar energy conversion. The highest efficiencies for TTA-UC systems have been achieved in liquid solution, owing to that several of the intermediate steps require close contact between the interacting species, something that is more easily achieved in diffusion-controlled environments. There is a good understanding of the kinetics dictating the performance in liquid TTA-UC systems, but so far, the community lacks cohesiveness in terms of how several important parameters are best determined experimentally. In this perspective, we discuss and present a “best practice” for the determination of several critical parameters in TTA-UC, namely triplet excited state energies, rate constants for triplet–triplet annihilation ($$k_{{{\text{TTA}}}}$$ k TTA ), triplet excited-state lifetimes ($$\tau_{{\text{T}}}$$ τ T ), and excitation threshold intensity ($$I_{{{\text{th}}}}$$ I th ). Finally, we introduce a newly developed method by which $$k_{{{\text{TTA}}}}$$ k TTA , $$\tau_{{\text{T}}}$$ τ T , and $$I_{{{\text{th}}}}$$ I th may be determined simultaneously using the same set of time-resolved emission measurements. The experiment can be performed with a simple experimental setup, be ran under mild excitation conditions, and entirely circumvents the need for more challenging nanosecond transient absorption measurements, a technique that previously has been required to extract $$k_{{{\text{TTA}}}}$$ k TTA . Our hope is that the discussions and methodologies presented herein will aid the photon upconversion community in performing more efficient and manageable experiments while maintaining—and sometimes increasing—the accuracy and validity of the extracted parameters.

Extracting accurate information from triplet–triplet annihilation upconversion data with a mass-conserving kinetic model

“…Edhborg et al recently outlined an approach for obtaining I th by determining the fraction of annihilator triplets that decay initially through TTA ( β ). 26 Their approach necessitates the collection of upconverted emission decay curves to determine β for a particular value of excitation irradiance. This process is repeated for a variety of irradiances to construct a plot of β vs.…”

High-Efficiency Near-Infrared-to-Visible Photon Upconversion in Poly(vinyl alcohol) Microporous Film

“…To gain insight into the kinetics of upconverted emissions in the films, time-resolved photoluminescence measurements were performed under various excitation powers by an 808 nm laser coupled with a square-wave pulse generator that was recently proposed to evaluate key characteristics in TTA-UC. 37,38 The pulse scheme and signal were confirmed by an oscilloscope trace (Supporting Information, Figure S2). Figure 3d and 3e show a gradual decrease in the decay time with an increase in excitation power.…”

“…Figure 3d and 3e show a gradual decrease in the decay time with an increase in excitation power. According to the literature, the key parameters from excitation-power-dependent decay plots can be determined by global fitting using the following expression: 15,36,38…”

Recyclable optical bioplastics platform for solid state red light harvestingviatriplet–triplet annihilation photon upconversion

“…The τ T was determined from the global fitting of excitation intensity-dependent up-conversion emission decay kinetics according to a previously developed method using eqn (1). 63–67 where I ( t ) is upconversion emission intensity, is the concentration of triplet excited annihilators at time zero, and β is a dimensionless parameter describing the relative initial rate of triplet deactivation by TTA and spontaneous triplet decay. 68 An increase in β with excitation intensity in sample-III confirmed a rise in annihilator triplet deactivation by TTA rather than spontaneous decay (Fig.…”

“…The  T was determined from the global fitting of excitation intensity-dependent up-conversion emission decay kinetics according to a previously developed method using equation 1. [63][64][65][66][67]…”