Synthesis, spectral, and thermal properties of K2CaP2O7:Sm3+ phosphors to fill the amber gap in LED applications

In this paper, novel Sm³⁺ doped K₂CaP₂O₇ phosphors emitting an orange reddish light for LEDs were prepared using solution combustion method. Powder X-ray diffraction, Rietveld refinement, FTIR, and scanning electron microscopy (SEM) techniques were utilised to determine the phase structure, functional groups, and surface morphology of the synthesized phosphors. The crystallographic analysis reveals the formation of single phase crystal structure with monoclinic symmetry and P21/n space group. The spectral properties were investigated by using the diffuse reflection (DR) spectra, photoluminescence (PL) emission and excitation spectra, and decay curves. The optical band for the optimized phosphor was determined to be 3.97 eV using the diffuse reflectance method. Under ultraviolet (UV), and blue light excitation of 403 nm, K₂CaP₂O₇:xSm³⁺ phosphors exhibit an orange red emission color due to the ⁴G_5/2 → ⁶H_5/2, ⁴G_5/2 → ⁶H_7/2, ⁴G_5/2 → ⁶H_9/2, and ⁴G_5/2 → ⁶H_11/2 transitions of the activator ion (Sm³⁺). The optimally doped phosphor was assessed to have a color purity of 98.38% with CIE coordinates as (x =0.58, y = 0.42). In addition, the thermal stability of the phosphor was investigated in the temperature range of 303 K- 703 K. It was observed that the emission intensity persisted up to 95.2% at 423 K with the high activation energy (ΔE) of 0.24 eV. All these results indicate that novel orange-red emitting K₂CaP₂O₇:Sm³⁺ phosphors can be used with n-UV chips to fill the amber gap in LED applications.