TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The nanoparticles are formed by heat-treating at 250-370 degrees C for 10 minutes-4 hours. The method further comprises forming the shell comprising mixing core nanoparticles solution with solution comprising precursor of M and/or gadolinium precursor, oleic acid and 1-octadecene to form third mixture of mixed core phase, mixing third mixture with lithium precursor, fluoride precursor and alcohol to prepare reaction solution, removing alcohol from the reaction solution by heating to form shell on the surface of the core, where the shell is made of lithium gadolinium metal fluoride of formula (LiGd1-rMrF4) (II).r = 0-1; andM = Y and/or lanthanide.Preferred Components: The nanophosphor nanoparticles have particle size of 1-150 nm, tetragonal or octahedral structure and exhibits up-conversion property. The nanophosphor further includes shell surrounding the core nanoparticles. The particle size of nanophosphor with core-shell structure is greater than 1-200 nm. In (II), when r is 0-less than 1, then (II) exhibits magnetism. The yttrium precursor is yttrium acetate, yttrium chloride and/or yttrium chloride hexahydrate. The gadolinium precursor is gadolinium acetate, gadolinium chloride and/or gadolinium chloride hexahydrate. The ytterbium precursor is ytterbium acetate, ytterbium chloride and/or ytterbium chloride hexahydrate. The erbium precursor is erbium acetate, erbium chloride and/or erbium chloride hexahydrate. The lithium precursor is lithium fluoride, lithium hydroxide, lithium hydroxide monohydrate. EXAMPLE - 0.35 mmole Gadolinium chloride hexahydrate, 0.45 mmole yttrium chloride hexahydrate, 0.18 mmole ytterbium chloride hexahydrate, 0.02 mmole erbium chloride hexahydrate and 3.1 mmole sodium oleate were dissolved in mixed solvent of water, ethanol and hexane at 70 degrees C for 4 hours to obtain a mixture. Then 10.5 ml oleic acid and 10.5 ml 1-octadecene were added to the obtained mixture, heated to 150 degrees C, dissolved, and then 2.5 mmol lithium hydroxide and methanolic solution of 4 mmol ammonium fluoride were added to the obtained solution to form reaction solution. The reaction solution was heated at 320 degrees C for 90 minutes to obtain lithium gadolinium yttrium fluoride nanophosphor of formula (LiGd0.35Y0.45:Yb3+0.18,Er3+0.02) (III). Mixed solution of 0.2 mmole gadolinium chloride hexahydrate, 10.5 ml oleic acid and 10.5 ml 1-octadecene was added to 10 ml chloroform dispersion of (III), uniformly mixed, then 2.5 mmole lithium hydroxide and 10 ml methanolic solution of 4 mmole ammonium fluoride were added, and the obtained solution was heated at 300 degrees C for 110 minutes to obtain lithium gadolinium fluoride coated nanophosphor with core-shell structure.