Ferroelectric materials with engineered thus visible-range optical band gaps are increasingly researched in recent years, triggering potentially new applications in solar cells, opto-ferroelectric devices, multifunctional sensors, and multisource energy harvesters. To date, most band gap engineered ferroelectrics have been discovered in form of ceramics fabricated via the solid-state route. Like other functional counterparts further research of these materials into nanoscale developments, e.g., nanocomposites and thin films, demands nanofabrication methods to be investigated. An emerging band gap engineered ferroelectric composition, (K,Na,Ba)(Ni,Nb)O3−δ (KNBNNO), discovered with solid-state route has allured research for novel applications as mentioned above. However, its nanofabrication via wet chemical routes has rarely been reported. In this paper, sol–gel method is used to fabricate KNBNNO nanoparticles. The developed method can successfully form the target perovskite phases, and is able to reduce the particle size from 300 to 400 nm made via the solid-state reaction to about 100 nm. In addition, the distributed particle size in the synthesized solutions averages at 4–6 nm, making the method suitable for potential thin film fabrication. Therefore, this paper offers a nanofabrication option to the emerging KNBNNO for prospective nanoscale research.

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Photosensors, photodetectors, or color sensors are key components for various optical and optoelectronic applications. Semiconductor‐based photodetection has been a dominator which is excellent at measuring the photon intensity of incident light. However, the wavelength of the incident light to be measured must be known beforehand and it mostly depends on auxiliary methods to filter unknown wavelengths. Herein, an alternative but simple mechanism that is using a monolithic, bandgap‐engineered photoferroelectric ceramic to blindly determine the wavelength and intensity of incident light at the same time is demonstrated. The photoferroelectric compound is Ba‐ and Ni‐codoped (K,Na)NbO3 exhibiting a direct bandgap of ≈2 eV and a spontaneous polarization of ≈0.25 C m−2. The band–band charge carrier transition is confirmed by multiple characterization methods of photoluminescence, photodielectric spectroscopy, and photoconductivity. The existent optoelectrical cumulative effect enabled by the simultaneous narrow bandgap and strong ferroelectricity allows to reliably distinguish the wavelengths of 405, 552, and 660 nm as well as the power density ranging from ≈0.1 to 10 W cm−2, with the photoresponsivity of up to 60 μA W−1. Consequently, this work proposes an alternative to semiconductor‐based counterparts for filterless, wavelength‐selective photodetection and color sensing.

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