The accuracy of ex situ characterization of InGaAsP materials for optoelectronics has been assessed by circulating a single specimen set among different laboratories. Six InGaAsP thin film specimens, with nominal photoluminescence (PL) peak wavelengths of 1.1, 1.3 and 1.5 mum, were measured with X-ray diffraction and PL. X-ray measurement reproducibility appears to be dominated by specimen nonuniformity. The distributions of the X-ray rocking-curve peak separations measured by the different laboratories had standard deviations from 1 to 11 arcsec, depending on the specimen, while the lateral variations across specimens were between 9 and 150 arcsec. In contrast, the variation among PL measurements was larger than the variation within individual samples. Consistent relative offsets between instruments were observed, but these had no apparent correlation with factors such as pump wavelength, wavelength calibration, sample temperature, pump power density, and peak identification. Analysis of the raw PL data with identical methods revealed that the variations are intrinsic to the data, not artifacts of the methods used to extract a characteristic energy from the PL spectra. (C) 2002 Elsevier Science B.V. All rights reserved.