Achieving tunable luminescence in rare earth free IRMOF-3 through post synthetic modifications by judicious choice of organic linker

Abstract

Owing to the high cost of rare earth ions/lanthanides, associated health hazard, mining issues and transport constrain, there is an urgent need of designing rare earth free functional materials. Globally lot of thrust has been given on designing cost effective lanthanides free phosphors for light emitting diodes. In addition to cost efficient and environmentally benign, these lanthanide free phosphors are free from doping induced defects, strain and distortions. Herein, two new functionalized Zn based isoreticular metal organic frameworks (IRMOFs) namely; IRMOF-SMA (sulfamic acid) and IRMOF-DPC (diphenyl phosphonic chloride) were synthesized via post synthetic modification (PSM) using IRMOF-3 for investigating the color tunable luminescence. The synthesized materials were characterized using powder X-ray diffraction (powder XRD), thermogravemetric analysis (TGA), fourier transformed infrared (FTIR), and nuclear magnetic resonance spectroscopy (NMR), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). For the first time, we have demonstrated tuning of intrinsic violet emission from pristine IRMOF-3 via PSM employing organic ligands viz. SMA and DPC. SMA leads to slight shift in emission hue from violet to blue but DPC leads to giant color shift from violet-blue to white light. The shift is correlated to electro negativity difference between sulfur and phosphorus, respectively, in SMA and DPC. Color correlated temperature evaluated for DPC linked IRMOF-3 was more than 5500 K suggest being bluish white (cool white). Enhancement in luminescence lifetime also observed with PSM MOFs compared to pristine sample owing to lowering of non-radiative transitions. This work opens up new avenues in the field of exploring MOFs for lanthanide optoelectronic devices and light emitting diodes and further tuning the light via PSM strategy.