Bright Upconversion Emission, Increased <i>T</i>_c, Enhanced Ferroelectric and Piezoelectric Properties in <scp><scp>E</scp></scp>r‐Doped <scp><scp>Ca</scp><scp>Bi</scp></scp>₄<scp><scp>Ti</scp></scp>₄<scp><scp>O</scp></scp>₁₅ Multifunctional Ferroelectric Oxides

<jats:p><jats:styled-content style="fixed-case"><jats:roman>Er</jats:roman></jats:styled-content><jats:sup>3+</jats:sup>‐doped <jats:styled-content style="fixed-case"><jats:roman>Ca</jats:roman><jats:roman>Bi</jats:roman></jats:styled-content><jats:sub>4</jats:sub><jats:styled-content style="fixed-case"><jats:roman>Ti</jats:roman></jats:styled-content><jats:sub>4</jats:sub><jats:styled-content style="fixed-case"><jats:roman>O</jats:roman></jats:styled-content><jats:sub>15</jats:sub> (<jats:styled-content style="fixed-case">CBT</jats:styled-content>) bismuth layer structured ferroelectric ceramics were synthesized by the solid state method. Photoluminescence (UC), dielectric, ferroelectric, and piezoelectric properties were systematically studied for the first time. The <jats:styled-content style="fixed-case"><jats:roman>Er</jats:roman></jats:styled-content><jats:sup>3+</jats:sup>‐doped <jats:styled-content style="fixed-case">CBT</jats:styled-content> sample showed a bright up‐conversion <jats:styled-content style="fixed-case">UC</jats:styled-content> while simultaneously obtaining an increased Curie temperature (<jats:italic>T</jats:italic><jats:sub>c</jats:sub>), enhanced ferroelectric and piezoelectric properties. The <jats:styled-content style="fixed-case">UC</jats:styled-content> properties of <jats:styled-content style="fixed-case"><jats:roman>Er</jats:roman></jats:styled-content><jats:sup>3+</jats:sup>‐doped <jats:styled-content style="fixed-case">CBT</jats:styled-content> were investigated as a function of <jats:styled-content style="fixed-case"><jats:roman>Er</jats:roman></jats:styled-content><jats:sup>3+</jats:sup> concentration and incident pump power. A bright green (556 nm) and a weak red (674 nm) emission bands were obtained under excitation (980 nm) at room temperature, which correspond to the transitions from <jats:sup>4</jats:sup><jats:styled-content style="fixed-case">S</jats:styled-content><jats:sub>3/2,</jats:sub> and <jats:sup>4</jats:sup><jats:styled-content style="fixed-case">F</jats:styled-content><jats:sub>9/2</jats:sub> to <jats:sup>4</jats:sup><jats:styled-content style="fixed-case">I</jats:styled-content><jats:sub>15/2</jats:sub>, respectively. The dependence of <jats:styled-content style="fixed-case">UC</jats:styled-content> emission intensity on pumping power indicated that three‐photon and two‐photon processes are involved in the green and red <jats:styled-content style="fixed-case">UC</jats:styled-content> emission, respectively. Studies on dielectric properties indicated that the introduction of <jats:styled-content style="fixed-case"><jats:roman>Er</jats:roman></jats:styled-content> increased the <jats:italic>T</jats:italic><jats:sub>c</jats:sub> with relatively smaller values of dielectric loss of <jats:styled-content style="fixed-case">CBT</jats:styled-content>, thus making this ceramic suitable for sensor applications at higher temperatures. Ferroelectric and piezoelectric measurements showed that the <jats:styled-content style="fixed-case"><jats:roman>Er</jats:roman></jats:styled-content><jats:sup>3+</jats:sup>‐doped ceramics showed an increase in remnant polarization and piezoelectric constant. As a multifunctional material, <jats:styled-content style="fixed-case"><jats:roman>Er</jats:roman></jats:styled-content>‐doped <jats:styled-content style="fixed-case">CBT</jats:styled-content> ferroelectric oxide showed great potential in sensor, optical‐electro integration, and coupling device applications.</jats:p>