Advanced functional materials that possess both persistent luminescence (PersL) and mechanoluminescence (ML) have gained considerable attention during the past few years owing to their potential applications in many fields such as two‐dimensional stress sensing, energy‐saving lighting, and optical bioimaging. However, combined investigation of PersL and ML is still in its infancy. Here, the optical property of Er ³⁺‐doped NaYF ₄, mainly focusing on the PersL and ML characteristic and their correlation, is studied in detail. It is shown that microscaled NaYF ₄:Er ³⁺ has advantages against nanoscaled counterpart in terms of PersL and ML, consistent with the photoluminescence results. By means of pre‐charging and trap‐emptying cycle and thermoluminescence test, it is confirmed that the PersL and ML of NaYF ₄:Er ³⁺ come from the same trapped charge carriers, and the ML belongs to the trap‐controlled ML …