Influence of NaCl-assisted precipitation on the red emission properties of Sr2SiO4:Eu3+ phosphor

A modified precipitation method, involving intermediate precipitation followed by calcination, has been applied for the first time to synthesize a series of Sr 2-x Eu x SiO 4 compounds (x = 0.00–0.10) using the SiO 2 –NaOH–SrCl 2 –Eu(NO 3 ) 3 system. The precipitation procedure, based on one-hour stirring of a boiling aqueous solution, leads to the in-situ formation of NaCl within the precipitates which are not filtered prior to calcination. Structural and optical characterizations (XRD, FTIR, and photoluminescence spectroscopy) have confirmed phase-pure α-Sr 2 SiO 4 :Eu 3+ with intense emission peaks assigned to characteristic Eu 3+ transitions, and maximum emission observed at x = 0.08. To evaluate the effect of NaCl, the optimized composition was compared with a similar sample prepared by a NaCl-free route. The NaCl-assisted synthesis promotes stabilization of the α-Sr 2 SiO 4 phase under relatively mild conditions and leads to a refined microstructure with reduced structural disorder and enhanced lattice-field effects. These factors result in increased emission intensity and unusual spectral behavior, namely a strong 5 D 0 → 7 F 4 transition with an intensity comparable to that of the hypersensitive 5 D 0 → 7 F 2 line, which is an uncommon feature in Eu 3+ -activated silicate hosts. Moreover, the synthesized phosphor exhibits a relatively long luminescence lifetime, high quantum efficiency (η ≈ 58%), a wide band gap (∼4.3 eV), and high color purity (∼90%). These findings demonstrate that NaCl can act as an in-situ formed flux and crystal-field modulator, offering a simple, environmentally friendly yet effective strategy to tailor the optical performance of Eu 3+ -doped orthosilicate phosphors for potential applications in solid-state lighting and optoelectronics.