Integrating Sphere Setup for the Traceable Measurement of Absolute Photoluminescence Quantum Yields in the Near Infrared

There is an increasing interest in chromophores absorbing and emitting in the near-infrared (NIR) spectral region, e.g., for applications as fluorescent reporters for optical imaging techniques and hence, in reliable methods for the characterization of their signal-relevant properties like the fluorescence quantum yield (Phi(f)) and brightness. The lack of well established Phi(f) standards for the NIR region in conjunction with the need for accurate Phi(f) measurements in transparent and scattering media encouraged us to built up an integrating sphere setup for spectrally resolved measurements of absolute fluorescence traceable to radiometric scales. Here, we present the design of this setup and its characterization and validation including an uncertainty budget for the determination of absolute Phi(f) in the visible and NIR To provide the basis for better measurements of Phi(f) in the spectral window from ca. 600 to 1000 nm used, e.g., for optical imaging, the absolute Phi(f) of a set of NIR chromophores covering this spectral region are measured and compared to relative values obtained using rhodamine 101 as Phi(f) standard. Additionally, the absolute Phi(f) values of some red dyes that are among the most commonly used labels in the life sciences are presented as well as the absolute quantum yield of an optical probe for tumor imaging.