New near-infrared emissions and energy transfer in Er3+ -doped MgAl layered double hydroxides.

Abstract

A series of Er3+ -doped magnesium aluminium layered double hydroxides (Er3+ -doped, MgAl-LDHs) with different Mg2+ /(Al3+ +Er3+ ) molar ratios were synthesized using the hydrothermal method. Compositional and structural analyses suggest that the Er3+ -doped MgAl-LDHs kept a hexagonal structure while the Mg2+ /(Al3+ +Er3+ ) molar ratio was at 1.0-4.1. The downconverted emission spectra of the Er3+ -doped MgAl-LDHs showed a red emission at 650 nm and strong infrared emissions at 720, 780, and 850 nm. These infrared emissions were hardly observed in previous downconverted emission spectra of Er3+ -doped materials. In the analysis of the Er3+ energy levels and in relevant published literature, the energy transfer diagram for Er3+ -doped in MgAl-LDHs is described, and infrared emissions at 720, 780, and 850 nm may be attributed to 4 F7/2 →4 I13/2 , 2 H11/2 →4 I13/2 , and 4 S3/2 →4 I13/2 transitions of Er3+ , respectively. Er3+ -doped MgAl-LDHs could have potential application as marking and targeting agents in the processes for drug delivery in consideration of the strong near-infrared Er3+ emissions, as well as the special layered structure of MgAl-LDH.