Absolute Method to Certify Quantum Yields of Photon Upconversion via Triplet–Triplet Annihilation

Abstract

For the consistent development of the field of photon upconversion via triplet−triplet annihilation (TTA-UC), it is pivotal to know the true quantum yield of TTA-UC emission. Although TTA-UC quantum yields have been determined by common relative measurements using quantum yield standards, there is still a discrepancy between the reported values even for the benchmark sensitizer−emitter pair of platinum(II) octaethylporphyrin (PtOEP) and 9,10-diphenylanthracene (DPA). Here, to resolve this situation, we show a method to obtain the absolute quantum yield of TTA-UC photoluminescence. The difficulty in obtaining absolute TTA-UC quantum yield by the integrating sphere measurement is to accurately calibrate the contribution of reabsorbed upconverted emission by triplet sensitizers. The reabsorption correction is successfully carried out by comparing sensitizer phosphorescence with and without the integrating sphere. An absolute TTA-UC quantum yield of the PtOEP−DPA pair is obtained as 36%, which shows a good agreement with the relative TTA-UC quantum yield. An absolute TTA-UC quantum yield of another red-to-blue TTA-UC pair, platinum(II) meso-tetraphenyltetrabenzoporphyrin (PtTPBP) and 2,5,8,11-tetra-tert-butylperylene (TTBP), is obtained as 27%. These absolute TTA-UC quantum yields can be used as certified values to check the measurement setup and sample condition for determining relative TTA-UC quantum yields in each laboratory.

Discovery of Key TIPS‐Naphthalene for Efficient Visible‐to‐UV Photon Upconversion under Sunlight and Room Light**

“…The η UC value of Ir(C6) 2 (acac) and TIPS‐Nph was determined as 20.5 % by the relative method (Figure 2 b, see the Supporting Information for details). The reliability of the high η UC was confirmed by a similar value of 21.4 % at 17 Wcm −2 obtained by the absolute method in the integrating sphere (see the Supporting Information for details) [33, 34] . This η UC is the highest value for vis‐to‐UV TTA‐UC ever reported and twice higher than the previous record (10.2 %) [32] .…”

Photon Upconverting Solid Films with Improved Efficiency for Endowing Perovskite Solar Cells with Near‐Infrared Sensitivity

“…Note that the Φ FL value is underestimated than the intrinsic film property due to the reabsorption of fluorescence by the donor in the integrating sphere. For the same reason, the absolute TTA‐UC efficiency Φ UC ′ of the film samples is inevitably underestimated, but it is difficult to precisely correct the contribution of reabsorption since the donor phosphorescence, necessary for the reabsorption calibration, [41] was too weak to detect.…”

“…TTA-UC efficiency was measured by using an absolute quantum yield measurement system C13534-01 (Hamamatsu Photonics). [41] The sample was held in an integrating sphere and excited by the laser excitation source (730 nm, 25 mW, RGB photonics). The scattered excitation light was removed using a 700 nm short-pass filter, and emitted light was monitored with a multichannel detector.…”

TIPS-Naphthalene for Efficient Visible-to-UV Photon Upconversion under Sunlight and Room Light

“…The reliability of the highest ηUC was confirmed by a similar value of 21.4% at 17.2 W cm −2 obtained by the absolute method in the integrating sphere (see SI for details). 33,34 This ηUC is the highest value for vis-to-UV TTA-UC ever reported and twice higher than the previous record (10.2%). 32 On the other hand when the previous best acceptor PPO 21,27,[30][31][32] was combined with Ir(C6)2(acac) in THF, no upconverted emission was observed ( Figure S6).…”

“…22 The highest UC value is certified by absolute quantum yield measurements. 33,34 Thanks to the strong visible absorption over 80,000 M −1 cm −1 and weak UV absorption of Ir(C6)2(acac), 22,35,36 the Ith value reaches a sub-solar irradiance without dropping the ηUC, resulting in the highest external UC efficiency ηUC,ext of 17.4% for vis-to-UV TTA-UC. Remarkably, an upconverted UV emission was also observed under an AM 1.5 solar simulator and desk LED light (Figure 1b-e).…”