A highly thermal-stable orange red emitting La(OH)₃:Sm³⁺ phosphor for w-LED and thermal sensor dual-applications

Abstract

The orange-red emitting La(OH)₃:Sm³⁺ (1–5 mol.%) phosphors are synthesized using urea-assisted solution combustion synthesis (SCS). The synthesized La(OH)₃:Sm³⁺ phosphors were validated by Rietveld refinement and X-ray diffraction (XRD) patterns and exhibit a single-phase structure, characterized by a hexagonal system with space group P63/m. At 250 nm, the phosphors display a charge transfer band (CTB) involving O2− and Sm3+, indicating intense excitation. La(OH)₃:Sm³⁺ phosphor exhibits distinctive peaks at 565, 604, 651, and 708 nm under 250 nm excitation, which correspond to the 5G₅/₂ → 6HJ (J = 5, 7, 9, 11) transitions. Among these, 604 nm exhibits the most intense emission. The optimal doping concentration of La(OH)₃:Sm³⁺ is x = 2 mol.%. Importantly, even as the temperature increases to 420 K, La(OH)₃:Sm³⁺ demonstrates exceptional thermal stability, retaining 86.38 % of its initial luminescence intensity. The La(OH)₃:2Sm³⁺ phosphor exhibits an activation energy (Ea) of 0.328 eV. The internal quantum efficiency (IQE) measures 50.09 %. The colour purity (CP) for each phosphor is calculated to be 96.50 %. Additionally, 405 nm chips are effectively used for fabricating single-coloured and white light-emitting diodes (w-LEDs). The Commission Internationale de l'Eclairage (CIE) coordinates of the packaged w-LED are (0.325, 0.350), with a high colour rendering index (CRI) of 90. These results from investigations show that orange-red emitting La(OH)₃:Sm³⁺ phosphors have potential for development lighting device materials.