Ultrasonic transducers have long relied on lead-based piezoelectric materials. However, the potential harm of lead to the environment and human health has spurred an urgent demand for environmentally friendly lead-free alternative materials. Bismuth sodium titanate (BNT) is regarded as a promising piezoelectric material for lead-free transducers due to its low dielectric constant and acoustic impedance. To address the problem that the previously developed 0.84BNT-0.133BKT-0.027BT composition still struggles to meet the requirements of high-quality biological tissue imaging, this study adopted an acceptor doping strategy and prepared a B-site Fe³⁺-doped lead-free piezoceramic system. The results show that appropriate Fe³⁺ doping produces a favorable balance between R3c/P4bm phase-structure modification and defect-related pinning, thereby enhancing the electromechanical response. At x = 0.01, the piezoelectric coefficient reaches the maximum value of 180 pC/N, while k_t reaches 0.42, indicating enhanced thickness-mode electromechanical coupling. The planar 10 MHz ultrasonic transducer fabricated with this composition exhibits high sensitivity, with an insertion loss |IL| of 16 dB. After introducing an acoustic focusing lens, the focused transducer achieves axial and lateral resolutions of 182 and 264 μm, respectively. In addition, clear imaging of the internal structure of a porcine eyeball and the surface of a commemorative coin was successfully achieved. These results confirm that the B-site Fe³⁺-doped modified BNT-BKT-BT ternary lead-free ceramic has great application potential in high-performance environmentally friendly medical ultrasonic transducers.

Optical temperature sensors have garnered significant attention because of their ability to provide accurate, noncontact temperature measurements. Rare-earth element-doped Gd₃Al₃Ga₂O₁₂ (GAGG) ceramics are known for their excellent optical properties, stable crystal structure, good thermal stability, and tunable fluorescence characteristics. In this study, we innovatively introduced a series of Pr³⁺-doped GAGG garnet ceramics with high sensitivity for optical temperature sensing. The phase structure, morphology, and optical properties of the ceramics were investigated, and the optimal doping concentration was determined. The photoluminescence (PL) and optical temperature sensing properties of the GAGG:Pr³⁺ ceramics were thoroughly examined. The PL spectra of the GAGG:Pr³⁺ garnet transparent ceramics displayed multiple narrow emission peaks, and CIE plots indicated that the luminescence color was tunable within the green region. The emission intensities exhibited a quenching phenomenon at high rare-earth element doping concentrations and elevated temperatures. The optical temperature sensing properties of GAGG:Pr³⁺ were analyzed via the fluorescence intensity ratio (FIR) method, which is based on Pr³⁺ thermally coupled (³P₁ → ³H₅ and ³P₀ → ³H₄) and nonthermally coupled (³P₁ → ³H₅ and ¹D₂ → ³H₄) energy level pairs. The maximum relative sensitivities for the thermally coupled and nonthermally coupled energy level pairs of GAGG:Pr³⁺ reached 0.81% K⁻¹ (at 300 K) and 0.37% K⁻¹ (at 350 K), respectively, under 450 nm blue light excitation. These results suggest that GAGG:Pr³⁺ ceramics have significant potential for noncontact optical temperature sensing applications.