In accordance with certain embodiments of the present disclosure, a method for adjusting the spectral detectivity of a thermal detector is described. The method includes coating the light sensitive portion of a thermal detector with a first material to reduce the response of the detector. The first material is coated with a second material that is thermally thin and has spectral absorption characteristics. The second material is coated with a third material that is thermally thick, whereby the spectral absorbance of the second material as filtered by the third material primarily determines the thermal conversion of the thermal detector.