The objective of this research was to demonstrate the extension of the current design of the Individual Identification Friend or Foe (IIFF) patch, to provide a response in the shortwave infrared (SWIR) region of the electromagnetic spectrum. The purpose of the IIFF patch is to mitigate fratricide during ground engagements, by emitting a near infrared (NIR) signal when the wearer is illuminated by a targeting laser attached to the shooter's weapon. Due to the proliferation of NIR Night Vision Devices (NVDs), it is desirable to produce a version of the patch that emits in the SWIR spectrum, making its response visible to operators with next-generation NVDs, while being invisible to conventional NVDs. This further enhances the "covert" nature of the IIFF patch. To produce SWIR output, a visible-light emitter is used in conjunction with a downconverting phosphor filter. This thesis develops and evaluates candidates for visible-light emitters and downconverting phosphor filters in order to determine the most suitable candidate for use in the IIFF patch. Three potential candidate materials, based on neodymium and ytterbium phosphors, were evaluated using photoluminescence excitation spectroscopy. A quantitative comparison of the combined efficiency was performed to select an initial optimized combination. SWIR emission was observed through an InGaAs imaging array. Approved for public release; distribution is unlimited. US Navy (USN) author. http://archive.org/details/visibletoswirdow109454715