Rare-earth glass reference materials for near-infrared spectrometry: correcting and exploiting temperature dependencies.

Quantitative descriptions of the location of seven near-infrared absorption bands as functions of temperature 5-50 degrees C are presented here for three recently introduced wavelength/wavenumber Standard Reference Materials (SRMs): SRM 2035, SRM 2065, and SRM 2036. For all bands in all three SRMs, locations are well described as linear models parametrized with the location at 0 degrees C (intercept) and the rate of location change per degrees C (slope). Since these materials were produced from compositionally similar melts, the slopes for each band are identical within measurement imprecision in all three SRMs; only minor differences are observed in the intercepts. Because the direction of change in location differs among the bands, it is possible to use the measured band locations to reliably estimate sample temperature. Two approaches to estimating temperature are evaluated: slope and measurement uncertainty-weighted means. While both methods work well with measurements made under well-characterized and stable environmental conditions, the more complex uncertainty-weighted analysis becomes relatively more predictive as the total measurement uncertainties increase.