The electron paramagnetic resonance (EPR) technique was employed to detect oxygen vacancy defects in the tetragonal Ba1− x Ca x TiO3 (x = 0.03) ceramics (BCa3T) prepared via the mixed oxide route at 1300–1500 °C. In the rhombohedral phase below −100 °C, an EPR signal at g = 1.955 appeared in the insulating BCa3T with an electrical resistivity of 108 Ω cm and was assigned to ionized oxygen vacancy defects. BCa3T prepared at 1300 °C showed a temperature-stable X6S dielectric specification (ε′ = 1750). Three types of vacancy defect, namely, Ba, Ti, and O vacances, could coexist in BCa3T owing to the partial Ti-site occupation by Ca2+.

CsPbBr3 quantum dots (QDs) prepared through traditional hot‐injection and room temperature reprecipitation methods are usually hexahedral (nanoplate/cube) and green‐emitting. These methods severely obstruct the development of blue perovskite‐based light‐emitting diodes (PeLEDs) because the resultant QDs always suffer unachievable morphology regulation. Here, highly efficient blue‐emitting rhombic dodecahedron CsPbBr3 QDs (CsPbBr3 <12> QDs) are obtained by regulating morphological transformation for the first time through a novel and facile sequential post‐treatment strategy. Hydrobromide (‐NH3+) with stronger adsorption energy promotes the morphology transform of QDs from nanoplate to cube by substituting oleylamine in the first step. Then, polar solvent vapor eliminates PbX64− and led to the (112) crystal plane of the cube QDs being exposed, which is effectively stabilized by ‐NH3+ to realize morphology transition from cube to the dodecahedron. Highly efficient 12‐faceted dodecahedrons are endowed with significantly enhanced photoluminescence quantum yield of 89.8% at 476 nm as well as uniform size distribution and mono‐dispersity. The target blue PeLEDs achieve the maximum external quantum efficiency of 6.6% (480 nm) and excellent spectrum stability. This study provides a new strategy to prepare blue‐emitting CsPbBr3 <12> QDs by delicate control toward the growth and polyhedron process of crystal.

Perovskite-based white-light-emitting devices (WLEDs) are expected to be the potential candidate for the next-generation lighting field due to their scalability and low-cost process. However, simple and adjustable WLED fabrication technology is in urgent need. Here, WLEDs with a single layer of perovskite quantum dots (PQDs) were constructed by combining Zn2+-doped CsPbBr3 PQDs with exciplex emission between poly­(9-vinylcarbazole) (PVK) and ((1-phenyl-1H-benzimidazol-2-yl)­benzene)) (TPBi). Zn2+-doped CsPbBr3 PQDs with polar ion shells were prepared by means of low temperature and post-treatment. The photoluminescence quantum yield (PLQY) can reach as high as 95.9% at the emission wavelength of 456 nm. The blue shift of its PL (∼60 nm) is much greater than that of other reported Zn2+-doped CsPbBr3 PQDs (5–10 nm), thus realizing the true blue-emission Zn2+-doped CsPbBr3 PQDs. As a result, just by controlling the thickness of TPBi, the adjustment of cold (CIE (0.2531, 0.2502)) and warm WLEDs (CIE (0.3561, 0.3562)) is realized for the first time.