Double perovskites, a class of ceramic oxides with unique crystal structures and diverse physical properties, show promise for various technological applications including solar cells, photodetectors, and light-emitting diodes (LEDs). Despite limited research on rare earth-doped double perovskites, leveraging their ultrahigh luminous efficiency to achieve bright yellow LED emission and addressing energy transfer challenges between Yb 3+ and Nd 3+ ions in double perovskite La 2 ZnTiO 6 with moderate phonon energy are explored in this work. Through phonon-assisted energy transfer, an ultrasensitive optical thermometer covering a wide temperature range is developed by utilizing the different temperature responses of Er 3+ emission in the visible light region and Nd 3+ emission in the near-infrared region based on the luminescence intensity ratio (LIR). All the results demonstrate that the rare earth (Yb−Er, Yb−Nd, and Yb−Nd−Er)-doped La 2 ZnTiO 6 phosphors can be effectively utilized for ultrabright LED illumination and ultrahigh sensitivity self-calibrated temperature sensing. This research underscores the significance of phonon-assisted energy transfer in improving material properties and provides valuable insights for the advancement of multifunctional materials.