A multispectral optical sensor incorporating quantum confinement devices is composed of a solid-state tunable filter, an optional lens, and a photodetector or plurality of photodetectors. The tunable filter is multilayered composite film of semiconducting materials, which includes a quantum well or other quantum confinement structure and barrier materials to ensure the proper confinement of charge carriers within the quantum well. The tunable filter is capable of acting as a long-pass filter. The approximate cut-on wavelength is established through selection of a well material with a bandgap near the desired energy, and barrier materials with a higher bandgap. For a given reference temperature the exact cut-on wavelength may be fixed through careful selection of the dimensions of the quantum confinement structures, whose quantum confinement energy is added to the bandgap energy to yield the cut-on energy. The operational cut-on wavelength at any given moment may be controlled through variation of the temperature of the tunable filter using onboard or external thermal control hardware and through control of an electric field applied across the filter.