Solar technologies require improved material performances or new materials functions, either to improve energy capture or to develop new conversion principles. This work presents a low cost pathway to realize 2D nanophotonic molybdenum crystals having a transition in their optical properties with a tunable cut-off wavelength. These nanostructured materials have a dual function. They can be used as selective solar absorbers and/or selective infrared emitters. This novel pathway for producing low cost nanostructured materials creates new opportunities for solar capture in Concentrated Solar Power, Solar Thermophotovoltaics, Solar Thermo-Electrical Generators and for infrared emission control in thermophotovoltaic technologies.