A budget-friendly integrating sphere for reliable quantum yield characterization of fluorescent solutions

Absolute fluorescence quantum yield (Φ f ) is a fundamental parameter for characterizing the photophysical behavior of fluorescent materials. This study presents the development of a budget-friendly integrating sphere system for accurate Φ f measurements in solution-phase samples. The 28 cm sphere was fabricated using resin-reinforced rubber and coated internally with white paint and barium sulfate (BaSO₄) to ensure diffuse reflectivity. The design includes orthogonal excitation and detection ports, a top-mounted sample holder, and a baffle placed to block direct optical paths between the excitation source and detector, thereby ensuring uniform light distribution. Φ f measurements were performed on standard dyes (Rhodamine B, Eosin B, and 2’,7’-Dichlorofluorescein) and a nonstandard fluorescent sample (orange highlighter ink) using 405 nm and 532 nm laser excitation. Repeatability was confirmed with relative standard deviation (RSD) values mostly below 6 %, and the combined relative uncertainty was estimated at ±7 % based on GUM principles. The Φ f values obtained for Rhodamine B (0.72 and 0.71), Eosin B (0.62 and 0.63), and 2’,7’-Dichlorofluorescein (0.90) showed good agreement with literature data, while the orange highlighter ink exhibited high Φ f (0.90 and 0.89), comparable to commercial dyes. These findings confirm that the proposed budget-friendly integrating sphere provides accurate, reproducible, and reliable fluorescence quantum yield data, making it well-suited for use in teaching and resource-limited research laboratories.