Energy bandgap of a semiconductor determines the spectral features of absorptions and emission processes and is one of the most important parameters for optoelectronic applications.Many applications such as solar cells,detectors,LEDs,and lasers can benefit greatly from semiconductors with any desired bandgaps or variable bandgaps in a wide range.Producing such semiconductors has been challenging using the traditional planar epitaxial technology.Nanomaterials such as nanowires and nanosheets open new opportunities of achieving any desired bandgap through alloying with almost arbitrary compositions.In this talk,our recent results are presented on growing and characterizing spatially composition-controlled alloys by combining spatial gradient of source materials with a temperature gradient in a CVD system.Using this dual gradient method,we demonstrated that a continuous spatial composition grading of single-crystal quaternary ZnxCd1-xSySe1-y alloy nanowires can be achieved over the complete bandgap range along the length of a substrate.The bandgap changes continuously from 3.55 eV (ZnS)to 1.75 eV(CdSe)in the example of ZnCdSSe alloy on a single substrate,with the corresponding light emission over the entire visible spectrum.Finally,composition control within a single nanostructure will also be demonstrated either as nanowires with axial composition control or nanosheets with multiple segments,allowing multi-color emission and lasing from a single nanoscale heterostructure.We will also show that even dynamical color control is possible with these nanostructures.Such unique alloy nanomaterial capabilities could potentially enable a range of applications including novel solar cells,solid state lighting,multispectral detection,or widely tunable lasing.Some of these examples of applications of alloy nano-materials will be discussed.