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The self-reduction of Eu3+ to Eu2+ and Ce4+ to Ce3+ can first be found by doping rare earth ions RE (RE = Eu, Ce) in Ba2CaB2Si4O14 (BCBSO). The Eu2+/Eu3+ codoped BCBSO and Ce4+/Ce3+ codoped BCBSO and Eu/Ce codoped BCBSO were synthesized by a high-temperature solid-phase method in air and reducing atmospheres, respectively. By comparing the photoluminescence spectra in air and reducing atmospheres, the self-reduction phenomenon of Eu3+ and Ce4+ in the BCBSO were verified adequately. The theoretical method of the bond energy was used to analyze the occupancy and self-reduction of Eu or Ce ions. The experimental results are in agreement with the theoretical ones. The color tuning phosphors were achieved in BCBSO:Eu and BCBSO:Ce. The codoped system BCBSO:Eu, Ce was studied and it was found that the position and shape of the emission spectra changed with the change in the excitation wavelength, and the change in the corresponding color could be seen from the CIE chromaticity coordinates. Its emission peak shifts from 481 to 595 nm with the increase in the Ce3+ concentration in the codoped system under the excitation of 365 nm. Based on the fluorescence lifetime, the energy transfer process between Eu2+–Ce3+ is proved, and its emission color can be adjusted to a certain extent.

The immersion method in which metal ions were used to toughen macromolecular chains to avoid the failure of hydrogel synthesis due to the rapid formation of coordination bonds in the gel precursor was often used to develop a robust gel. However, the uneven distribution of ions inside the hydrogel was harmful for its sensing performance by soaking. Herein, a robust polyacrylamide/gelatin/ZrOCl 2 •8H 2 O (PG-Zr 4+ ) hydrogel was developed by a straightforward strategy to toughen gelatin chains with Zr 4+ . The PG-Zr 4+ hydrogel held not only a high transparency (73%), robust fracture strength (0.842 MPa), and outstanding toughness (4 MJ m −3 ) but also fast self-recovery and satisfactory conductivity. Furthermore, the crystallization peak of the PG-Zr 4+ hydrogel disappeared at −60 to 25 °C with the introduction of dimethyl sulfoxide (DMSO) as a cryoprotectant; it could still exhibit stable electrical responses to weak stimuli of 1% strain at −20 °C for 24 h. Surprisingly, when simply assembled into a strain sensor with a gauge factor (GF) of 5.817, it was capable of precise real-time monitoring of both subtle pronunciation signals and drastic joint movements. This work opened the door to develop flexible wearable devices with multiple advantages.