Figure 1. Summary of the Nd³⁺ random laser operation.

(a) Simplified energy levels diagram of the Nd³⁺ ions. The upward arrows indicate the excitation wavelengths which correspond to the maximum of the absorption transitions and the downward arrow indicates the random laser transition at 1062 nm. (b) Diffuse reflectance spectrum of the Nd_0.10Y_0.90Al₃(BO₃)₄ nanocrystals with the Nd³⁺ absorption transitions labeled by the peak wavelengths indicated in Fig. 1(a).