<p>The discovery of novel high-efficiency red-emitting phosphors is great meaningful for the achievement of high color rendering index white LED, but still a challenge due to the strict crystal field limitation. Herein, we present a novel red-emitting phosphor K₃GdSi₂O₇: Eu²⁺ synthesized by high-temperature solid-state reaction. The crystal structure, photoluminescence (PL) properties, quantum efficiency, decay lifetime and thermal stability of the phosphor are investigated on detailed. The Eu²⁺ ions occupy the K⁺(3) crystallographic sites firstly, then reside the Gd³⁺ sites for the higher Eu²⁺-doped sample. The emission spectra of those phosphors consist of a broad red emission bands around 550–800&#xa0;nm with a full width at half maximum (FWHM) of 155&#xa0;nm upon the excitation at 365–400&#xa0;nm. Two different Eu²⁺ red-emitting centers are identified by the PL spectra and temperature-dependent PL spectra. The emission of Eu²⁺ ions in K₃GdSi₂O₇: Eu²⁺ phosphor resided at different crystallographic sites display different thermal properties. The concentration quenching mechanism of Eu²⁺ in K₃GdSi₂O₇ is determined. The fluorescence lifetimes of the as-prepared K₃GdSi₂O₇: Eu²⁺ samples are several microseconds and the temperature-dependent luminescence indicated K₃GdSi₂O₇: Eu²⁺ is medium thermal-stable. K₃GdSi₂O₇: Eu²⁺ is applied to white LED, which shows a correlated color temperature (CCT) of 3985 <i>K</i>, a color rendering index (CRI) of 92, and CIE color coordinate of (0.3766, 0.3607). Our results indicate that novel red-emitting K₃GdSi₂O₇: Eu²⁺ phosphors are expected to have potential application in warm white LEDs.</p>