The upconversion quantum yield (UCQY): a review to standardize the measurement methodology, improve comparability, and define efficiency standards

Abstract

Advancing the upconversion materials field relies on accurate and contrastable photoluminescence efficiency measurements, which are characterised by the absolute upconversion quantum yield (UCQY). However, the methodology for such measurements cannot be extrapolated directly from traditional photoluminescence quantum yield techniques, primarily due to issues that arise from the non-linear behaviour of the UC process. Subsequently, no UCQY standards exist, and significant variations in their reported magnitude can occur between laboratories. In this work, our aim is to provide a path for determining and reporting the most reliable UCQYs possible, by addressing all the effects and uncertainties that influence its value. Here the UCQY standard, at a given excitation power density, is defined under a range of stated experimental conditions, environmental conditions, material properties, and influential effects that have been estimated or corrected for. A broad range of UCQYs reported for various UC materials are scrutinized and categorized based on our assertion of the provided information associated with each value. This is crucial for improved comparability with other types of photoluminescent materials, and in addition, the next generation of UC materials can be built on top of these reliable standards.

Nanoengineering Triplet–Triplet Annihilation Upconversion: From Materials to Real-World Applications

“…The second commonly used method for UC QY measurement is a relative method which uses either a fluorimeter or spectrometer to compare the integrated upconverted photoluminescence to the integrated photoluminescence of an established standard. However, this method is often considered less accurate due to the high concentrations of sensitizer and annihilator required in upconversion samples. , High concentrations can lead to absorptance well above 0.1 (against IUPAC recommendations) and cause issues with comparison to the reference standard as well . For straightforward low-scattering and highly absorbing samples, the absolute integrating sphere method presents an accurate and relatively simple way to measure UC QY …”

“…Sen = sensitizer molecule, An = annihilator molecule, CT = charge-transfer state, 1 Sen or 1 An or 1 CT = singlet, 3 Sen or 3 An or 3 samples. 51,53 High concentrations can lead to absorptance well above 0.1 (against IUPAC recommendations 54 ) and cause issues with comparison to the reference standard as well. 51 For straightforward low-scattering and highly absorbing samples, the absolute integrating sphere method presents an accurate and relatively simple way to measure UC QY.…”

Regioselective electrophilic aromatic borylation as a method for synthesising sterically hindered benzothiadiazole fluorophores

“…PLQYs measurements were obtained following the conventions and considerations from Jones et al , 36 using a FLS920 spectrofluorometer (Edinburgh Instruments Ltd) equipped with an extended red-sensitive photon multiplier detector (R2658P, Hamamatsu) and an integrating sphere with a 102 mm inner diameter (Yobin Yvon) were used for all PLQY measurements. For the excitation, a 450 W xenon lamp (Xe2, Edinburgh Instruments Ltd) was employed.…”

Centimeter-Scale Curing Depths in Laser-Assisted 3D Printing of Photopolymers Enabled by Er3+ Upconversion and Green Light-Absorbing Photosensitizer

“…A calibrated spectrofluorometer (FLS920, Edinburgh Instruments, Livingston, UK) was used for spectral measurements, equipped with a 102 mm inner diameter integrating sphere (HORIBA Jobin-Yvon, Edison, New Jersey, US) and a 980 nm laser diode (LSR980NL-3W, Lasever Inc., Ningbo, China) used for excitation. As shown in Equation ( 1) [14], the external photoluminescence quantum yield (PLQY) was determined by dividing the number of emitted photons (N ) by the number of absorbed photons (N ):…”

“…Erbium (Er 3+ )/Yb 3+ co-doped NaYF 4 is one of the most efficient UC materials [13][14][15]. The green emissions from 2 H 11/2 → 4 I 15/2 (525 nm) and 4 S 3/2 → 4 I 15/2 (547 nm) transitions in Er 3+ /Yb 3+ co-doped systems, as shown in Figure 1a, typically involve two-photon UC (n = 2) [5,16,17].…”