Discovering new phosphors with narrow-band emission is critical for white light emitting diodes (LEDs) in liquid-crystal displays (LCDs). Herein, near-ultraviolet (UV) excitable narrow-band blue-emitting MBe₂(PO₄)₂:Eu²⁺ (M = Ca, Sr) phosphors were successfully designed, exhibiting an extremely narrow full width at half-maximum of ∼26–27 nm, high color purity of ∼99.1%, small Stokes shift of ∼1500 cm⁻¹, desirable photoluminescence quantum efficiency of ∼63.4%, and zero thermal quenching even at temperatures up to ∼300 °C. The small Stokes shift and narrow emission profile are fundamentally caused by the greatly suppressed structural relaxation benefiting from the rigid and ordered connected [BeO₄] and [PO₄] tetrahedra network. Meanwhile, the unprecedented thermal emission behavior is ascribed to the suppression of thermally activated photoionization and the non-radiative pathway from the cross-point of the 5d excited state to the 4f ground state of Eu²⁺. A wide color gamut reaching up to 88.6% NTSC is realized, demonstrating the validity of MBe₂(PO₄)₂:Eu²⁺ in LED backlights for LCDs. The present studies encourage researchers to identify hitherto undiscovered narrow-band phosphors via selecting a stiff and ordered host with confined sites for doped rare earth activators.