Effect of surfactants on the dual-mode photoluminescence properties of the NaYb0.48Gd0.5F4:2%Er3+ nanoparticles

• NaYb 0.48 Gd 0.5 F 4 :2%Er 3+ (NYGF:Er 3+ ) NPs were synthesised using various surfactants • The effects of chitosan, CTAB, SDS, and PVP were investigated • Under 380 nm excitation, the PLQY increased from 9 to 98% for the PVP system • Under 980 nm excitation, the UC emissions were originated via two-photon emission process. This study investigates the impact of surfactants, chitosan, cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulphate (SDS), and polyvinylpyrrolidone (PVP), on the structural, optical, and photoluminescent (PL) properties of NaYb 0.48 Gd 0.5 F 4 :2%Er 3+ nanoparticles (NPs). TEM confirmed the hexagonal morphology with surfactant-induced particle growth. Downconversion (DC) PL spectra exhibited enhanced red emission, with quantum yields reaching 48% (CTAB), 63% (SDS), and 98% (PVP), a dramatic improvement over the surfactant-free sample (9%). DC PL spectra indicated superior internal ordering in the CTAB (τ₃ = 526.5 μs), balanced surface passivation with PVP (τ₁ = 16.2 μs; τ₃ = 513.6 μs), and effective stabilization for SDS. The upconversion (UC) spectra exhibited several emissions via two photon process and further improved by CTAB. These results highlight the critical role of surfactants in optimizing luminescence performance and emphasize on two-fold significance, an intrinsic photophysical processes and extrinsic surface modifications in determining DC/UC luminescence for different targeted applications.