A dual-excited and dual near-infrared emission phosphor Mg14Ge5O24:Cr3+,Cr4+ with a super broad band for biological detection

Abstract

Recently, near-infrared phosphors that can be applied in many fields such as night vision, agriculture, and bio-applications have attracted considerable interest in the research field worldwide. Herein, a multi-functional and dual-excited near-infrared phosphor Mg₁₄Ge₅O₂₄:Cr³⁺,Cr⁴⁺ which provides two emission bands ranging from 700 nm to 1100 nm and 1100 nm to 1700 nm has been obtained via the traditional high-temperature solid state reaction. The presence of six and four coordination ions in the olivine structure of Mg₁₄Ge₅O₂₄ provides a favorable environment for the coexistence of Cr³⁺ and Cr⁴⁺. Under blue light excitation, a super broad emission band ranging from 650 nm to 1100 nm with a full-width at half maximum (FWHM) of 266 nm is assigned to the spin-allowed ⁴T₂ (4F) → ⁴A₂ transition of Cr³⁺ in a weak crystal-field environment. With the increase in the concentration of Cr ions, more and more Cr⁴⁺ preferentially occupies four coordinated Ge⁴⁺ sites, and the other broad emission band ranging from 1100 nm to 1600 nm with a FWHM of 256 nm that comes from the ³T₂ → ³A₂ transition of Cr⁴⁺ is observed. The phenomenon of NIR I region excitation and NIR II region emission appears. The transmission experiment of a biological tissue proves that the Mg₁₄Ge₅O₂₄:Cr³⁺,Cr⁴⁺ phosphor has potential applications in the field of near-infrared light-emitting diodes for biological detection.