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[Display omitted] • This work overcomes the trade-off challenge between particle size and quantum efficiency of nitride phosphors encountered in traditional preparation methods. • The underlying mechanism is clarified to be the increased Eu2+ percentage and the unaltered chemical stiffness after the mechanochemical processing. • Small-sized nitride phosphors with superhigh brightness and ultralong durability. High brightness mini-LED backlit displays attract extensive advanced applications. However, it is a challenge to develop small-sized phosphors concurrently satisfying high brightness and long-term durability to accommodate mini-LED chips. Herein, a two-step facile approach combining high-temperature sintering and mechanochemical milling is proposed to obtain small-sized β-Sialon:Eu nitride phosphors (D50 = 3.13 μm) with a five-fold increase in quantum efficiency (QE, 16% → 79%) and a superb on chip durability with 100% maintenance of QE for 1400 h. The high performance is attributed to the increased Eu2+ percentage (67% → 77%) and the unaltered chemical stiffness after the mechanochemical processing. Crucially, β-Sialon:Eu film made from small-sized powders shows higher packaging density and better light uniformity, concomitantly with an improved QE of 83%. Moreover, this approach is generally applicable to other robust nitride phosphors. By using small-sized β-Sialon:Eu and (Sr,Ca)AlSiN 3 :Eu films, as-fabricated mini-LED backlights simultaneously achieve a superhigh brightness of 302,150 nits and an ultralong durability exceeding 2,000 h, opening up an avenue for mini-LED backlit displays being a viable technology for high-end applications. [ABSTRACT FROM AUTHOR]