NOVELTY - The core/multi-shell semiconductor nanocrystal comprises a core material made of III/V compound and 2 or more shell materials. Shell material (I) coats the core material, and sequentially each subsequent shell material coats the preceding shell. Each shell material is chosen from II/VI, III/V or III/VI compound. The core material is different from shell material (I), and any shell material is different from the shell material of adjacent shells. The nanocrystal exhibits a type-I band offset and luminescence at a wavelength of 400-1600 nm.    USE - For wideband optical amplifiers, light-emitting diodes, biological labeling agents, photoelectric devices, laser devices, optical data communication systems, and host materials (all claimed), and in therapeutic or diagnostic methods.    ADVANTAGE - The core/multi-shell semiconductor nanocrystal yields exceptional fluorescence quantum yield which remains very high even upon ligand exchange and transformation to water environment. The nanocrystal exhibits narrow distribution of sizes leading to excellent emission spectra, and has excellent stability.    DETAILED DESCRIPTION - The core/multi-shell semiconductor nanocrystal comprises a core material made of III/V compound and 2 or more shell materials. Shell material (I) coats the core material, shell material (II) coats shell material (I), and sequentially each subsequent shell material coats the preceding shell. Each shell material is chosen from II/VI, III/V or III/VI compound. The core material is different from shell material (I), and any shell material is different from the shell material of adjacent shells. The nanocrystal exhibits a type-I band offset and luminescence at a wavelength of 400-1600 nm. INDEPENDENT CLAIMS are included for the following:    (1) manufacture of core/multi-shell semiconductor nanocrystal;    (2) wideband optical amplifier;    (3) light-emitting diode;    (4) biological labeling agent;    (5) photoelectric device;    (6) laser device;    (7) optical data communication system; and    (8) host material.