Delaminated layered rare-earth hydroxide composites with ortho-coumaric acid: color-tunable luminescence and blue emission due to energy transfer

We demonstrate a novel example of delaminated layered rare-earth hydroxide (LRH, R = Tb, Y) composites with ortho-coumaric acid (CMA) and surfactant 1-octane sulfonic (OS) anions that exhibit tunable photoluminescence, especially blue emission due to energy transfer via the layer Tb³⁺. Different molar ratios of organic guests (OS/CMA) and layer ions (Tb/Y) give rise to versatile composites of OS_xCMA_1-x-LTb_yY_1-yH (x = 0.9, 0.8, 0.7, 0.6, 0.5, y = 1, 0.9, 0.7, 0.5, 0.3, 0.1, 0). In the solid state, for LTbH composites, co-quenching for emissions of CMA and the layer Tb³⁺ is found, while for LYH composites, green emission (502 nm) is observed. In formamide (FM), all of the composites are found to be facilely delaminated, and the colloidal suspensions of LTbH composites with varied OS_xCMA_1-x interlayer guests exhibit color-tuning within the blue-light region (430-465 nm), with blue-shift of emissions and enhanced luminescence intensity following increased OS content. LTb_yY_1-yH composites (with a fixed OS/CMA ratio of 0.7 : 0.3), however, present emissions from blue to green with increased Y³⁺ content. A new concept of 'host-energy transfer-induced-emission (HETIE)' is proposed to explain the blue luminescence via energy transfer of the host Tb³⁺. The intriguing energy transfer between a photoactive host matrix and interlayer guests in the delaminated state offers a promising approach to achieve efficient tuning of luminescence, thus meeting the high demand of applications on multicolor optical and display devices; especially blue emission.