A method of making shape-adaptable and spectral-selective distributed optical radiation sources, in the wavelength range between UV and mid-infrared, for therapeutic treatment using passive host medium containing nanocrystals is disclosed. The spectral output of the distributed optical radiation source is controlled by the nanocrystal size distribution that determines the spectral output of fluorescence radiation originating from these nanocrystals from within the said host medium, which contains the said nanocrystals, under excitation by an external source. The size of nanocrystals, or the size distribution of nanocrystals, incorporated in the host medium is selected based on the radiation spectral output required for therapeutic requirements. The passive host medium, incorporating the said nanocrystals, is made of adaptable, geometrically configurable, material that conforms to any desired shape.