Synergistic effects of europium doping on MOF-5: exploring its photoluminescent and non-linear optical behaviour for enhanced optical limiting

Metal-organic frameworks (MOFs) are researched widely for their linear optical properties, while their non-linear optical (NLO) properties are rarely investigated. This report discusses the behaviour of MOF-5 and its ability to bond with a europium moiety to exploit its NLO properties using the <i>Z</i>-scan technique. A partial deterioration in the Raman spectra and quenching of light in the PL spectra in some samples emphasised the need to study their ability to exhibit phosphorescence. TR-PL analysis revealed nanosecond lifetime values, which were attributed to their ability to fluoresce owing to the weak bonding between the 1,4-benzenedicarboxylic linker and europium ions. The same deterioration was found in the non-linear absorption studies for these samples. Enhanced structural and optical properties were found in the 1% doped sample (M_1) that exhibited a reverse saturable absorption (RSA) in the <i>Z</i>-scan technique, which led us to find its optical limiting threshold (1.53 × 10¹² W m^-2) and non-linear absorption co-efficient (<i>β</i> = 2.12 × 10^-10 mW^-1). An intensity-dependent non-linear absorption study revealed the presence of sequential two-photon absorption. These cumulative findings emphasize the potential of Eu³⁺-doped MOF-5 as a promising material for NLO applications, with the M_1 sample demonstrating the best optical performance amongst the pure and doped MOF-5 samples.