Just Accepted Articles have been posted online after technical editing and typesetting for immediate view. The final edited version with page numbers will appear in the Current Issue soon.
The long-standing absence of standardized assessment protocols for bulk photochromic materials has hindered reliable performance comparisons across studies reported by different research groups. Here, we introduce a standardized testing protocol along with a set of nine key parameters—coloration rate constant, bleaching rate constant, half-life, photostable equilibrium constant, optical modulation range, contrast ratio, response time, cycling stability and coloration efficiency—for evaluating the performance of bulk photochromic materials. Using photochromic inorganic-organic hybrid phosphonate-lanthanide-polyoxoniobates (RA-Ln-PONb, Ln = Dy, Eu, Lu; RA = risedronic acid) as a case study, we successfully validate the rationality of this protocol and demonstrate that these parameters collectively enable a comprehensive, multi-dimensional assessment of photochromic performance. This work provides an important methodological foundation for comparative studies of different bulk photochromic materials.