Excitation-power mediated optical hysteresis behavior in a single one-dimensional upconverting microcrystal

Abstract

Optical hysteresis behavior (OHB) is of great importance for technological applications including optical data switching and manipulation. In this study, the power-dependent luminescent property of a single one-dimensional NaYbF₄:X³⁺ (X = Er, Ho, and Tm) microcrystal was systematically investigated. We observed the interesting OHB that a system exhibits two different optical responses for the same laser input. A series of real colour luminescence patterns with information-rich upconversion cryptography were also obtained, which offers great opportunities for optical barcoding at the single particle level. The intrinsic OHB strongly depends on excitation approach, excitation power density range, Yb³⁺ concentration and sample crystallinity rather than active center. The underlying mechanisms of the intrinsic OHB and luminescence loss were explored, and a mechanism based on permanent local structural changes and intrinsic defect induced luminescence quenching is proposed. The laser thermal effect was confirmed by decreased luminescence intensity ratio of ²H_11/2 → ⁴I_15/2 to ⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺ as the excitation power increased. The luminescent loss includes both irreversible and reversible processes, and these two processes can be distinguished via excitation power cycling experiments. Reversible luminescence loss contributed to defect quenching due to energy migration from Yb³⁺ to the native defects, and irreversible luminescence quenching originated from the thermally induced permanent local structural changes of microcrystals. This work not only enables a deeper understanding of power-dependent OHB in related systems, but also provides the new dimensions for special applications such as multilevel anti-counterfeiting and intelligent memory storage.