Mini-LED backlights, combining color conversion materials with blue Mini-LED chips, promise traditional liquid crystal displays (LCDs) with higher luminance, better contrast and wider color gamut. As color conversion materials, Cd- or Pb-based quantum dots are usually toxic and unstable, and commercially available inorganic phosphors are quite stable and cheap, but they have a large size due to their synthesis at high temperature, and their quantum efficiency and reliability are size dependent. To make inorganic phosphors to be well combined with Mini-LED chips (usually 100 x100 μm in size) in the emerging Mini-LED backlights, the particle size of the phosphors needs to be reduced to several micrometers or sub-micrometers while the quantum efficiency remains unchanged. In this work, we prepared fine nitride phosphors by treating commercially available phosphors, including CaAlSiN₃:Eu²⁺ and (Sr, Ba)₂Si₅N₈:Eu²⁺, with ball milling, centrifuging and acid washing. The particle size of phosphors can be easily controlled by the milling speed, and the phosphors with a size varying from 0.5 to 15 mm were thus obtained. The samples remained the comparable quantum efficiency with the original ones even when their particle size was reduced to 2 μm as they contained less surface defects after acid washing. We demonstrated that red-emitting Mini-LEDs can be fabricated by combining the red phosphors with blue Mini-LED chips, which show higher external quantum efficiency, luminance and stability than those made by using quantum dots. It indicates that fine and high efficiency phosphors can be obtained by the proposed method in this work, and they have great potentials for use in Mini-LED displays.