Commercially available options for unattended gamma-ray spectrometry in harsh environments use either scintillators or room-temperature semiconductors. However, these detectors have relatively high power requirements because pulse processing electronics must be "always on" to record the energy of each incident event, and are prohibitively expensive if sensors are to be considered "one-time-use" data-gathering tools, or deployed in large numbers. A rugged, inexpensive zero or ultra-low-power gamma-ray spectrometer would be suitable for use in many types of unattended radiation detection applications including instrumented cargo containers, covert surveillance, nonproliferation monitoring, and long-term environmental measurements. Many of the shortcomings of commercially available spectrometers could be overcome using a passive gamma-ray spectrometry method based on optically stimulated luminescence (OSL) materials. Such an instrument would be "passive" in that attenuating materials are used to modulate the gamma flux incident on an array of OSL crystals. The incident energy spectrum is unfolded from the relative total energy deposited in each crystal. Readout can occur long after exposure to the gamma-ray flux, thanks to the "memory" inherent in OSL materials. This enables the fabrication of zero and low-power gamma-ray spectrometers. Because the components of the OSL spectrometer are all quite inexpensive and suitable for harsh operating environments, this new spectrometer would offer the combination of low cost, ruggedness and low-power operation lacking in commercially available spectrometers. We are currently performing simulations and analysis to prove the concept of the OSL spectrometer and are pursuing DOE funding to perform device fabrication and demonstration measurements.