Compositional tuning in KLa(Gd)F4:RE3+ nanoparticles reveals a strong correlation among crystal phase, upconversion emission, and magnetic response. In the systematic compositions of KLa(0.79–x)GdxF4:1% Er3+/20% Yb3+ (x = 0–0.5), the progressive Gd3+ substitution induces a transformation from a cubic to a hexagonal crystal phase. This phase evolution governs the upconversion photoluminescence under 980 nm excitation, producing pronounced color switching from yellow to red emissions. The nanoparticles simultaneously exhibit composition-dependent magnetic behavior, transitioning from paramagnetism at room-temperature to superparamagnetism at 5 K, with the fully hexagonal composition (x = 0.50) reaching a saturation magnetization of 105.74 emu g–1. Electron paramagnetic resonance confirms that higher Gd3+ content strengthens magnetic interactions between neighboring Gd3+ ions. The present comprehensive understanding of structural, upconversion emission and magnetic features enable the rational design of multifunctional lanthanide nanomaterials with implications for bioimaging, theranostics, and optoelectronic technologies.
Deo et al. (Sat,) studied this question.