TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The element (A) of metal or non-metal is zinc, gallium, indium, sulfur and/or tellurium. The precursor (A) and precursor (B) are reacted in the presence of nanocrystals (a) to form nanocrystal shell of magnesium selenide or its alloy on the surface of the nanocrystals (a). Nanocrystals (a) are group III-V or group II-VI semiconductor nanocrystal core or core-shell-type semiconductor nanocrystals having group III-V or group II-VI semiconductor nanocrystals as shell. nanoparticles including nanocrystals of magnesium-selenium-complex compound of formula: MgaAbSe, preferably magnesium selenide. Nanoparticles have multi-shell structure, and nanocrystals of magnesium-selenium-complex compound are present as interlayer between group III-V semiconductor nanocrystals and group II-VI semiconductor nanocrystals. Group III-V semiconductor nanocrystals are binary element compound chosen from gallium nitride, gallium phosphide, gallium arsenide, gallium antimonide, aluminum nitride, aluminum phosphide, aluminum arsenide, aluminum antimonide, indium nitride, indium phosphide, indium arsenide and/or indium antimonide, ternary element compound chosen from gallium nitrogen phosphide, gallium nitrogen arsenide, gallium nitrogen antimonide, gallium phosphorus arsenide, gallium phosphorus antimonide, aluminum nitrogen phosphide, aluminum nitrogen arsenide, aluminum nitrogen antimonide, aluminum phosphorus arsenide, aluminum phosphorus antimonide, indium nitrogen phosphide, indium-nitrogen arsenide, indium nitrogen arsenide, indium nitride antimonide, indium phosphorus arsenide, indium phosphorus antimonide, and/or gallium nitrogen phosphide, or quaternary element compound chosen from gallium aluminum nitrogen arsenide, gallium aluminum nitrogen antimonide, gallium aluminum phosphorus arsenide, gallium aluminum phosphorus antimonide, gallium indium nitrogen phosphide, gallium indium nitrogen arsenide, gallium indium nitrogen antimonide, gallium indium phosphorus arsenide, gallium indium phosphorus antimonide, indium aluminum nitrogen phosphide, indium aluminum nitrogen phosphide, indium aluminum nitrogen arsenide, indium aluminum nitrogen antimonide, indium aluminum phosphorus arsenide, indium aluminum phosphorus arsenide, and/or indium aluminum phosphorus antimonide. Group II-VI compound is binary element compound chosen from cadmium selenide, cadmium telluride, zinc sulfide, zinc selenide, zinc telluride, zinc oxide, mercury selenide, mercury telluride, magnesium selenium and/or magnesium sulfide, ternary element compound chosen from cadmium selenium sulfide, cadmium selenium telluride, cadmium sulfur telluride, zinc selenium sulfide, zinc selenium telluride, zinc sulfur telluride, mercury selenium sulfide, mercury selenium telluride, mercury sulfur telluride, cadmium zinc sulfide, cadmium zinc selenide, cadmium zinc telluride, cadmium mercury sulfide, cadmium mercury selenide, cadmium mercury telluride, mercury zinc sulfide, mercury zinc selenide, mercury zinc telluride, magnesium zinc telluride, magnesium zinc selenide, and/or magnesium zinc sulfide, or quaternary element compound chosen from mercury-zinc-tellurium sulfide, cadmium-zinc selenium sulfide, cadmium-zinc-selenium telluride, cadmium-zinc-sulfur telluride, cadmium-mercury-selenium sulfide, cadmium-mercury selenium telluride, cadmium-mercury-sulfur-telluride, mercury-zinc-selenium sulfide, mercury-zinc-selenium-telluride, and/or mercury-zinc-sulfur-telluride.a+b=1;a=more than 0 to 1;b=more than 0 to less than 1;andA=group II metal other than magnesium, group III metal, group V non-metal element and/or group VI non-metal element other than selenium.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The precursor (A) is alkylated magnesium compound, complex of magnesium metal and phosphine compound, complex of magnesium metal and thiol compound, magnesium halide, magnesium cyanide, magnesium amide, cycloalkenyl magnesium compound, cycloalkyl magnesium compound, allyl magnesium compound, bis(cyclopentadienyl)magnesium, and/or magnesium phthalocyanine. The precursor (B) is a complex consisting of selenium and a compound chosen from dialkyl phosphine, diaryl phosphine, trialkyl phosphine and/or triaryl phosphine, and bis(trialkylsilyl)selenide, diphenyl selenide, alkyl selenide, cycloalkenyl selenide and/or cycloalkyl selenide. The organic solvent is 6-22C primary alkyl amine, 6-22C secondary alkyl amine, 6-40C t-alkyl amine, heterocyclic compound containing nitrogen atom, 6-40C olefin, 6-40C aliphatic hydrocarbon, aromatic hydrocarbon substituted with 6-30C alkyl group, and/or phosphine substituted with 6-22C alkyl group. The ligand compound is chosen from primary amino group-containing compound (RNH2), secondary amino group-containing compound ((R)2NH), imino group-containing compound ((R)3N), thio group-containing compound (RSH) and phosphorus-containing compound ((R)3P), preferably methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, octylamine, dodecylamine, hexadecylamine, oleylamine, octadecylamine, dimethylamine, diethylamine, dipropylamine, methylphosphine, ethylphosphine, propylphosphine, butylphosphine, pentylphosphine, diphenylphosphine and/or triphenylphosphine. The reaction of precursor (A) and precursor (B) involves reacting precursors (A and B) together with precursor (C) that contains element (A) of metal or non-metal other magnesium and selenium.R=1-24C alkyl, 2-24C alkenyl or 5-20C aryl.