## 1 Introduction  
Lithium niobate (LiNbO\({}_{3}\), LN) crystals have established themselves as pre-eminent candidates for holographic volume storage applications owing to their exceptional electro-optic coefficients and nonlinear optical properties [1, 2]. Nevertheless, the practical deployment of undoped LiNbO\({}_{3}\) in advanced storage systems faces substantial barriers stemming from inherent recombination centers, ionic mobility restrictions, volatile charge retention, and pronounced optical susceptibility [3]. To circumvent these limitations, recent advances have focused on the strategic incorporation of transition metal dopants (e.g., Fe\({}^{3+}\), Cu\({}^{2+}\), Mn\({}^{2+}\), Ni\({}^{2+}\)), which engineer defect-mediated bandgap states to regulate carrier dynamics and amplify the photorefractive response through controlled electron-hole trapping mechanisms [4, 5, 6]. Among transition metal-doped LiNbO\({}_{3}\) systems, iron-doped crystals (Fe:LiNbO\({}_{3}\)) have emerged as benchmark materials, achieving saturation diffraction efficiencies exceeding 70% at 488 nm illumination while demonstrating exceptional hologram stability, with grating persistence exceeding several months under dark storage conditions [7]. This material has enabled groundbreaking progress in volumetric data storage, notably demonstrated by the successful encoding of 10,000 high-resolution holograms within a 5.0 mm-thick crystal, achieving a record volumetric density of 6.7 Gbits/cm\({}^{3}\)[8] and facilitating correlation recognition systems with 95% operational accuracy [9]. Despite these advances, Fe:LiNbO\({}_{3}\) crystals remain constrained by two critical shortcomings: inherent fan-out scattering noise arising from photovoltaic field anisotropies and intrinsically slow response kinetics, which collectively impede their deployment in real-time storage architectures [10]. Recent advances in multi-element co-doping have yielded notable progress in non-volatile holographic storage, with Mn:Fe:LiNbO\({}_{3}\), Tb:Fe:LiNbO\({}_{3}\), and Ce:Cu:LiNbO\({}_{3}\) crystals demonstrating enhanced charge retention and spatial phase stability under prolonged illumination [11; 12; 13; 14; 15]. Among these systems, dual doping with Fe\({}^{3+}\) and Cu\({}^{2+}\) has proven particularly effective: Fe:Cu:LiNbO\({}_{3}\) crystals exhibit a 60-fold acceleration in writing speed and a 67-fold increase in sensitivity compared to single-doped analogues, attributed to synergistic electron-hole trapping at multivalent defect sites [16; 17]. Despite these improvements, persistent limitations in secondary response kinetics underscore the need for advanced defect engineering approaches. Building on these developments, the strategic integration of optical-damage-resistant ions (e.g., Mg\({}^{2+}\), Sc\({}^{3+}\), In\({}^{3+}\), Hf\({}^{4+}\), Zr\({}^{4+}\)) with photorefractive species has emerged as a promising strategy for suppressing intrinsic lattice defects and optimizing charge carrier dynamics [18; 19; 20; 21; 22]. Particularly noteworthy is Zn\({}^{2+}\) doping, which exhibits exceptional multifunctionality: At concentrations above 6.2 mol%, it simultaneously enhances the photorefractive response while achieving an unprecedented \(\sim\)200-fold improvement in photodamage resistance compared to undoped counterparts [23; 24; 25; 26]. This unique dual-action mechanism establishes Zn\({}^{2+}\) as a paradigm-shifting dopant for engineering high-performance holographic storage media. In this study, we present an innovative Zn:Fe:Cu:LiNbO\({}_{3}\) crystal system that synergistically integrates Zn\({}^{2+}\) ion doping with dual photorefractive centers (Fe\({}^{3+}\) and Cu\({}^{2+}\)). Building upon prior investigations by our group, high-concentration Zn\({}^{2+}\) doping in Cu:Fe:LiNbO\({}_{3}\) crystals significantly improves structural homogeneity, a critical factor in minimizing holographic distortion and noise during recording/readout processes [27].