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Emergence of photoluminescence enhancement of Eu3+ doped BiOCl single-crystalline nanosheets at reduced vertical dimensions.

Here, we report that a reduction in scale leads to an enhancement in the photoluminescence (PL) of Eu3+ doped BiOCl nanosheets, challenging the long-standing notion that PL is inevitably suppressed at a scale of tens of nanometers. The oriented depolarization effect of layered ferroelectrics was utilized for the first time to improve the PL efficiency of lanthanide doped nanomaterials. The probing effect of the electric dipole transitions of the Eu3+ ions and their PL measurements provides evidence that the depolarization field and the PL of Eu3+ ions increase synchronously as the thickness of the BiOCl single-crystalline nanosheets decreases from hundreds to tens of nanometers. We show that the scale-dependent internal electric field (IEF) induced by the depolarization field as well as its excitation field enhancement are responsible for the appearance of an abnormal scale-dependent PL enhancement. This finding may be useful for the development of low-dimensional material systems with enhanced photophysical properties, relevant for use in new nano-optoelectronic devices.