The gadolinium effect on crystallization behavior and luminescence of β‐NaYF 4 :Yb,Er phase

Single phase β‐NaY 0.8‐ x Gd x Yb 0.18 Er 0.02 F 4 nanoparticles with different concentrations of gadolinium ions were prepared via PVP‐assisted solvothermal treating at 200°C (PVP‐ polyvinylpyrrolidone). With the increase in Gd 3+ concentration, size of the nanoparticles decreased. The up‐converting spectra recorded upon 980 nm irradiation showed the green (510‐560 nm) and red (640‐690 nm) emissions, due to 2 H 11/2 , 4 S 3/2  →  4 I 15/2 and 4 F 9/2  →  4 I 15/2 transitions, respectively. The strongest up‐conversion luminescence was detected in 15 mol% Gd 3+ ‐doped nanoparticles obtained after 20 hours of solvothermal treating. With the rise of Gd 3+ content up‐conversion emission decreased due to increased defect concentration in the NaYF 4 matrix. Fourier transform infrared spectroscopy proved in situ generation of hydrophilic nanoparticles as a result of PVP ligands retention at the particle surface.