In this work, flower-like hierarchical ZnO:Nd³⁺/Yb³⁺ microstructures were successfully synthesized via a direct current arc plasma discharge method, using Zn powder, Nd₂O₃, and Yb₂O₃ as starting materials in an oxygen atmosphere. The crystal structure, phase purity, and vibrational properties were systematically investigated by XRD, Raman spectroscopy, and XPS, all of which confirm that the products crystallize in the hexagonal wurtzite structure with no detectable impurity phases. The observed slight shifts of diffraction peaks toward lower angles, along with the XPS signals of Nd 3d and Yb 4d core levels, evidence the successful substitution of Zn²⁺ lattice sites by the larger Nd³⁺ and Yb³⁺ ions. SEM observations reveal a distinctive three-dimensional hierarchical morphology, in which each flower-like microstructure (≈3~4 um in size) consists of multiple radially grown branches, and each branch is assembled from closely packed nanorods of varying diameters. This unique architecture provides a large specific surface area that is expected to facilitate efficient energy transfer and enhance upconversion performance. Under 980 nm laser excitation, the samples exhibit characteristic UC emission peaks centered at approximately 540, 601, 661, 756, 806, and 870 nm, all arising from intra-4f transitions of Nd³⁺ ions. Power-dependent UC measurements demonstrate that the emissions at 540 nm and 601 nm involve two- to three-photon processes, the 661 nm and 756 nm emissions are dominated by two-photon processes, and the 806 nm near-infrared emission shows a mixed one- and two-photon behavior. An interesting phenomenon is observed in this system: the visible emission intensities are significantly stronger than the near-infrared emissions, which is opposite to most previously reported Nd³⁺/Yb³⁺ co-doped materials. This intensity reversal is attributed to a cross-relaxation process (⁴F_3/2+⁴F_3/2 → ⁴I1_3/2+(²G_9/2+⁴G_7/2)) that consumes population on the ⁴F_3/2 level while populating the higher-lying emitting states, thereby enhancing visible emissions at the expense of NIR emissions. Temperature-dependent luminescence spectra were recorded over a wide range from 298 K to 573 K. As temperature rises, the visible emissions and the 870 nm NIR emission gradually decrease in intensity due to thermal quenching, whereas the 756 nm and 806 nm NIR emissions exhibit an anomalous increase, which is ascribed to phonon-assisted energy transfer and thermal population effects. Based on these distinct thermal responses, dual-mode optical thermometers were constructed using the fluorescence intensity ratio technique. For the TCL pair composed of (⁴S_3/2+⁴F_7/2) and (²H_9/2+⁴F_5/2), the FIR(I_{756 nm}/I_{806 nm}) follows the Boltzmann distribution, yielding an energy gap of approximately 743 cm-1 and a maximum relative sensitivity of 1.20% K^-1 at 298 K. For the NTCL modes, using the pairs of (⁴S_3/2+⁴F_7/2) vs. (²G_9/2+⁴G_7/2) and (²H_9/2+⁴F_5/2) vs. (²G_9/2+⁴G_7/2), the FIR values are well fitted by the Struck-Fonger model, and the corresponding maximum relative sensitivities reach 4.70% K^-1 and 3.58% K^-1, respectively, with temperature resolutions as low as 0.0064 K and 0.0084 K. These figures of merit compare favorably with those of most previously reported Nd³⁺/Yb³⁺ co-doped systems. The exceptional thermometric performance is mainly attributed to the abundant defects introduced by large-ion doping in the hierarchical microstructure, which enhance electron – phonon interactions and make the FIR response more sensitive to temperature variations. The combination of TCL and NTCL strategies within a single material not only overcomes the spectral overlap and sensitivity limitations inherent in conventional single-mode thermometry but also provides self-calibration capability and reliable signal readout across a broad operational temperature range. These results demonstrate that the ZnO:Nd³⁺/Yb³⁺ flower-like hierarchical microstructures are promising candidates for practical non-contact optical thermometry applications in complex environments, such as biomedical thermal monitoring, microelectronic device diagnostics, and microfluidic temperature sensing.