Dual active luminescence centers from a single-solid composite SnO2:Eu3+/Al-MCM-41: defect chemistry mediated color tuning for white light emission

Abstract

In this work, we report on white light generation by defect chemistry modification in a single-solid SnO₂:Eu³⁺/Al-MCM-41 composite. The samples were carefully characterized by X-ray diffraction, transmission electron microscopy, N₂ adsorption-desorption isotherms, UV-vis diffuse reflectance spectra and luminescence spectra. It is found that the mesoporous material Al-MCM-41 with a large specific surface area (1040 m² g⁻¹) and narrow pore size distribution (2.7 nm) was successfully prepared via pretreating kaolin through a simple ball milling approach. SnO₂:Eu³⁺ nanocrystals with fine crystalline nature and ultra-small particle sizes were successfully incorporated into the channels of the host matrix Al-MCM-41 through a hydrothermal route. Contrary to the theoretical predictions of the quantum size effects, SnO₂:Eu³⁺/Al-MCM-41 composites showed an abnormal band gap narrowing with particle size reduction, which can be well-defined as a function of surface defects and Eu³⁺ doping effects. By varying the Sn/Si molar ratios and Eu³⁺ doping concentration, the highly defective SnO₂:Eu³⁺/Al-MCM-41 composites exhibited tunable defect chemistry mediated broad band emission and typical Eu³⁺ red emission that could modulate the color of light and improve the color rendering index (CRI). As a result, a maximum external quantum efficiency of 37.2% and white light with the color coordinates of (0.26, 0.22) in the CIE1931 color space were observed for the SnO₂:(6.13%)Eu³⁺/Al-MCM-41 composite with a Sn/Si molar ratio of 0.183 when it was excited by near-ultraviolet light.