Magnetoluminescent Bifunctional Dysprosium-Based Phosphotungstates with Synthesis and Correlations between Structures and Properties

Abstract

A series of dysprosium-based lacunary Keggin-type phosphotungstates have been prepared by the reaction of the preformed polyoxometalate (POM) precursor [P2W19O69(OH2)]14– and Dy3+ ions in the solution of organic carboxylic acid. Four POM-ligated lanthanide derivatives display four classes of configurations: three dimeric POMs with 2:1 type K2[N(CH3)4]5H4[Dy(α-PW11O39)2]·21H2O (1Dy), 2:2 type Na2[N(CH3)4]4H2[{Dy(α-PW11O39)(H2O)3}2]·28H2O (2Dy), and 2:3 type K8H3[(DyOH2)3(CO3)(α-PW9O34)2]·30H2O (3Dy), together with a tetrameric 4:8 type K14H12[Dy8(PW10O38)4(OH)4(H2O)2 (W3O14)]·57H2O (4Dy). These complexes exhibit the bifunction of luminescence and SMM properties, which indicate a bright prospect in optomagnetic devices. The solid-state fluorescence spectra of 1Dy–4Dy all show yellowish green emission resulting from the characteristic 4f–4f transitions of Dy3+ ions. However, it is interesting that 1Dy including only mononuclear Dy3+ ion has the highest luminous intensity and longest decay time in the visible or near-infrared region. Static magnetic studies reveal that 1Dy–3Dy show the thermal depopulation of Dy3+ Stark sublevels, whereas 4Dy displays the dominant ferromagnetic interactions within Dy3+ ions in the low temperatures as well as the thermal depopulation of Dy3+ Stark sublevels. The field-induced single molecule magnet (SMM) behaviors of 1Dy–4Dy are demonstrated by dynamic magnetic studies.