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The value of spin-orbit splitting Δ0 of gallium phosphide (GaP) nanoparticles was determined.The information concing the spin-orbit splitting of the valence band at Γ was acquired using fluorescence and infrared spectroscopes.Detailed investigation on the fluorescence characteristics under ultraviolet photoexcitation reveals that two doublets of emission transitions are related to the spin-orbit splitting of the valence band.The origin of two broad violet emissions,3.00 and 3.10 eV,can be attributed to the direct transitions near theΓ point of the Brillouin zone between the Γ1 conduction band and Γ15 valance band,that is,Γ6c-Γ8v and Γ6c-Γ7v,respectively.The origin of two blue emissions,2.74 and 2.64 eV,can be attributed to the indirect transitions between the X1 conduction band and Γ15 valance band,that is,Δ5c-Γ8vand Δ5c-Γ7v,respectively.Based on these transitions,the spin-orbit splitting Δ0 of the GaP nanoparticles is determined as 0.10 eV.The infrared spectrum of the GaP nanoparticles shows a band at 817 cm-1 which is assigned to the transition between the Γ7v and Γav valence band maxima.It follows therefore that the spin-orbit splitting Δ0 is 0.10 eV.