Evaluation of a Commercial Integrating Sphere Setup for the Determination of Absolute Photoluminescence Quantum Yields of Dilute Dye Solutions

Abstract

The commercial availability of stand-alone setups for the determination of absolute photoluminescence quantum yields (Phi(f)) in conjunction with the increasing use of integrating sphere accessories for spectrofluorometers is expected to have a considerable influence not only on the characterization of chromophore systems for use in optical and opto-electronic devices, but also on the determination of this key parameter for (bio)analytically relevant dyes and functional luminophores. Despite the huge potential of systems measuring absolute Phi(f) values and the renewed interest in dependable data, evaluated protocols for even the most elementary case, the determination of the fluorescence quantum yield of transparent dilute solutions of small organic dyes with integrating sphere methods, are still missing. This encouraged us to evaluate the performance and sources of uncertainty of a simple commercial integrating sphere setup with dilute solutions of two of the best characterized fluorescence quantum yield standards, quinine sulfate dihydrate and rhodamine 101, strongly differing in spectral overlap between absorption and emission. Special attention is dedicated to illustrate common pitfalls of this approach, thereby deriving simple procedures to minimize measurement uncertainties and improve the comparability of data for the broad community of users of fluorescence techniques.

Determination of the photoluminescence quantum yield of dilute dye solutions (IUPAC Technical Report)

“…The absolute Φ f of some of these commercially available dyes were only very recently re-measured [36,38,40,42,44], thereby also providing a complete purity analysis. Popular standards include quinine sulfate with all its problematic features-complicated ground-state chemistry [70,71], dependence of emission band position on excitation wavelength [72]-together with fluorescein and rhodamine 6G and rhodamine 101 recommended for the vis region [36,38,41,44].…”

“…Popular standards include quinine sulfate with all its problematic features-complicated ground-state chemistry [70,71], dependence of emission band position on excitation wavelength [72]-together with fluorescein and rhodamine 6G and rhodamine 101 recommended for the vis region [36,38,41,44]. The wavelength dependence of Φ f of quinine sulfate was only recently re-measured, thereby underlining its potential as quantum yield standard [42]. Fluorescein suffers from its sensitivity to acid-base chemistry and its photo chemical instability [24,32].…”

“…Especially for dyes showing a very small Stokes shift such as fluorescein, rhodamines, anthracene, or most cyanines and BODIPY dyes, the use of very dilute solutions is necessary to eliminate or at least minimize inner-filter or re-absorption effects [1, 36,38,41,44,81,82]. Re-absorption effects are typically accompanied by a red shift in emission with increasing dye concentration [36,38,42], whereas the absorption spectra are not affected by dye concentration. The use of very dilute solutions is also necessary for dyes showing self-or concentration quenching when the aim of the measurement is to obtain a molecular parameter characteristic for the monomeric dye [50,51] and not the Φ f value of a solution containing a mixture of monomeric and aggregated dyes.…”

“…Since Vavilov first introduced both the term "fluorescence yield" and a method for its determination for fluorescent organic dyes in liquid solution [17,18], numerous publications have appeared that deal with measurements of fluorescence quantum yields and/or suggested or recommended quantum yield standards [1, 16,19,[34][35][36][37][38][39][40]. However, despite the obvious and ever increasing importance of Φ f , at present, there are only very few overall accepted recommendations for the comparatively simple determination of this quantity even for transparent, dilute solutions available [28,30,36,40] as well as only very few reports on achievable measurement uncertainties [36,38,41,42]. This includes a recent assessment of measurement uncertainties related to each step required for the relative measurement of Φ f employing similar excitation wavelengths for sample and standard, a dye transfer chain approach, and the use of different excitation wavelengths in conjunction with an excitation correction as well as absolute measurements of Φ f with two different integrating spheres, a custom-made and a commercial setup [36,38,42].…”

“…However, despite the obvious and ever increasing importance of Φ f , at present, there are only very few overall accepted recommendations for the comparatively simple determination of this quantity even for transparent, dilute solutions available [28,30,36,40] as well as only very few reports on achievable measurement uncertainties [36,38,41,42]. This includes a recent assessment of measurement uncertainties related to each step required for the relative measurement of Φ f employing similar excitation wavelengths for sample and standard, a dye transfer chain approach, and the use of different excitation wavelengths in conjunction with an excitation correction as well as absolute measurements of Φ f with two different integrating spheres, a custom-made and a commercial setup [36,38,42]. In addition, a few application notes have been provided by instrument manufactures [43], yet no approved guidelines or technical notes exist at present.…”