Luminescence tuning and single-phase white light emitters based on rare earth ions doped into a bismuth coordination network

Abstract

The coordination network consisting of trivalent bismuth ions and pyromellitic acid (H₄Pyr), [Bi(HPyr)], was successfully applied as a host matrix for in situ incorporation of trivalent rare earth (RE³⁺) ions Sm³⁺, Eu³⁺, Tb³⁺ and Dy³⁺. High-throughput methods for hydrothermal synthesis allowed us to prepare and study the phase purity and crystallinity of the sample series, accelerating and facilitating the comparison between the synthesis parameters. Infrared absorption spectroscopy, elemental and thermogravimetric analysis, scanning electron microscopy and energy-dispersive X-ray spectroscopy, as well as powder X-ray diffraction and refinement of the unit cell parameters of the compounds, indicated that doping did not affect the structure, crystallinity, morphology and thermal stability of the matrix. The study of the spectroscopic luminescence properties of the nondoped and doped [Bi(HPyr)] allowed investigation of the sensitization processes of dopant RE³⁺ ions. The characteristic spectroscopic properties of the Eu³⁺ ion were used to study the incorporation site and coordination environment of the dopant by calculation of the experimental intensity parameters Ω_λ (λ: 2 and 4) and intrinsic quantum yield of the Eu³⁺ single-doped [Bi(HPyr)]. Straightforward emission color tuning by changing the relative concentrations of the dopant ions is possible and has been studied for the four systems double-doped with Tb³⁺:Eu³⁺, Tb³⁺:Sm³⁺, Dy³⁺:Eu³⁺ and Dy³⁺:Sm³⁺ ions. The Dy-containing systems show different shades of white emission and a wide range of correlated color temperatures (CCT), ranging from 2500 to 7500 K, hence being a promising candidate for the development of single-phase white light emitting devices.