P. Priyanka, S.P. Khatkar, V.B. Taxak, P. Boora
Keywords: photoluminescent, europium, IR, NMR spectroscopy, coligand
Summary:Over the past few decades, research work devoted to the analysis of the spontaneous emission enhancement from electric dipole transitions in lanthanide ions is extensively explored but a comprehensive work analyzing the results on the magnetic dipole transitions, which would be highly useful for researcher, is missing. But the recent progress in nanofabrication has triggered the investigation of magnetic side of spontaneous emission. The emission from magnetic dipole transitions provide an additional method to broadly tune the emission spectra of lanthanide ions, which act as important emitters in various technologies such as laser, lighting, displays and fiber amplifiers. Hence, a europium complex Eu(IPA)3.dmph was synthesized by using 3-isopropylpyrazole-5-carboxylic acid (IPA) as main ligand and 5,6-dimethyl-1,10-phenanthroline (dmph) as coligand via solution precipitation method. The Eu(IPA)3.dmph complex was characterized by means of elemental analysis, IR, UV-visible, photoluminescence (PL) spectroscopy and thermogravimetric analysis. The thermal studies show that complex is thermally stable up to 380 °C. UV-Vis spectra of complex exhibits two bands, one strong band from 200-300 nm and another weak band from 300-450 nm assigned to π→π* and n→π* ligand centered transitions respectively. The photoluminescent studies of complexes shows the dominance of magnetic dipole transition 5D0→7F1 over the electric dipole transition 5D0→7F2 and transitions from higher excited states are also observed, which provide an additional method to tune the emission spectra of complexes. The time decay curve of complex clearly reveals the presence of single luminescent centre . The lifetime value of complex is quiet high (2.6 ms), which is calculated by fitting the decay profile into single exponential equation I=I_0 exp(-t/ τ ) where τ is radiative decay time and I and I0 are luminescence intensity at time t and 0, respectively. The large value of luminescent lifetime is desired for important applications such as efficient laser operation, single photon sources, fluorescent microscopy and nanoscale imaging. Generally, europium(III) complexes emit red light, but, the color coordinates of complex are fall in blue region. The blue light emitting materials are one of the components in fabrication of white light emitting diodes. This color tunability is attributed to dominance of magnetic dipole transition and transition from higher excited state. These results have led to development of nanoscale probe for measuring magnetic local density of states directly. The spectral studies also shows that these results open new field of spectral tuning through magnetic dipole transition as well as electric dipole transition. Various information related to this field still have to be explored in future. Further, enhancement of magnetic side of spontaneous emission poses a challenging quest on researchers which leads to development of optical devices fully exploiting the magnetic nature of light in near future.