CMOS sensors are sensitive to infrared light. Usually a filter is used to block IR light to ensure correct focusing and exposure in the range of visible light.
Some older digital cameras do not have such a filter. This can easily be verified by "looking" into the emitter of any IR remore control through the camera's sensor and pressing a button on the remote control. If you can see the IR led in the camera's viewfinder, the camera is sensitive to IR.
Next step would be to insert the unknown filter between remote control and camera and check again. If the remote control's LED is visibly dimmed, the filter is an IR filter. If there is no change (compared to the image without the additional filter) the filter is not an IR filter, possibly a UC filter then.
BTW: For true infrared photography the filter on a modern digital camera needs to be removed