Engineering Red‐Emitting Bi ₇ Ti ₄ NbO ₂₁ :Eu ³⁺ Phosphors for Dual Applications in Solid‐State Illumination and Temperature Sensing

ABSTRACT In this study, orange‐red emitting Eu 3+ ‐doped Bi 7 Ti 4 NbO 21 (bismuth titanium niobate) (BTN) phosphors were successfully synthesized via the conventional high‐temperature solid‐state reaction (SSR) method. X‐ray diffraction (XRD) confirmed phase purity, with diffraction peaks closely matching the JCPDS Card No. 00‐031‐0202 for both undoped and Eu 3+ ‐doped samples. Scanning electron microscopy (SEM) revealed irregular, micrometer‐sized particles with mild agglomeration, suitable for photonic applications. Fourier‐transform infrared (FT‐IR) spectroscopy identified key vibrational modes within the BTN matrix, while the band gap was estimated using Tauc's method from diffuse reflectance spectra (DRS). DRS also indicated electronic transitions attributed to Eu 3+ 4f orbitals. Photoluminescence (PL) measurements under 366‐nm excitation displayed strong orange‐red emission, with CIE coordinates at (0.6109, 0.3885). PL decay curves followed a bi‐exponential trend at 595 nm emission, and increasing Eu 3+ concentration led to reduced lifetimes (τ) due to energy migration among ions. Temperature‐dependent PL (TDPL) analysis showed a peak relative sensitivity of ~0.71% K −1 at 298 K, highlighting potential for optical temperature sensing. The combined structural, optical, and thermal characteristics underscore the suitability of Eu 3+ ‐doped BTN phosphors for advanced solid‐state lighting, particularly in white LED and thermal sensing applications.