The linear absorption spectra of the samples were similar

The samples containing Ag NPs, used in the experiments , were labeled as: A (0.9% Ho3+; 0.6% Tm3+; 3.2% Yb3+; 1.0% AgNO3; HT: 12 h); B (0.9% Ho3+; 0.6% Tm3+; 3.2% Yb3+; 1.0% AgNO3; HT: 24 h); C (0.65% Ho3+; 0.6% Tm3+; 3.2% Yb3+; 2.5% AgNO3; HT: 24 h); D (0.65% Ho3+; 0.6% Tm3+; 3.2% Yb3+; 2.5% AgNO3; HT: 12 h).
A 200 kV transmission electron microscope (TEM) was used to determine the sizes and shapes of the silver NPs. A commercial spectrophotometer was used to measure the optical absorption spectra from 400 to 2000 nm. The PL measurements were made by exciting the samples using a 980 nm continuous-wave diode laser (maximum power on the samples: 200 mW).