Sm3+ doped tetragonal lanthanum molybdate: A novel host sensitized reddish orange emitting nanophosphor

A series of trivalent samarium doped lanthanum molybdate nanophosphors were prepared by co-precipitation route. The formation of highly crystalline tetragonal nanocrystals with space group I41/a is identified from powder X-ray diffractogram. The morphology and the oriented attachment mediated growth mechanism of the nanocrystals were recognized from TEM analysis. The strong and broad charge transfer band in the near ultra violet region favours excellent excitation of the nanophosphors and the energy transfer from host matrix to Sm³⁺ ions is established on account of the characteristic emissions of trivalent samarium ions upon host sensitization. The Judd-Ofelt (JO) theoretical analysis was carried out to have an insight into the spectroscopic characteristics of La_2-xSm_x(MoO₄)₃ nanophosphors. The relatively higher value of Ω₂ predicts more asymmetric environment of Sm³⁺ sites in the host lattice, favouring the dominance of electric dipole transitions and the various radiative parameters are evaluated. In spite of the excitation channel, the ⁴G_5/2 → ⁶H_9/2 transition of Sm³⁺ observed at 645 nm is the most prominent emission transition. The maximum emission intensity is observed for La_1.98Sm_0.02(MoO₄)₃ nanophosphors and as the doping concentration exceeds this limit, there will be fall in emission intensity due to concentration quenching effect. A detailed investigation on the decay behaviour of host sensitized and direct excited emission of samarium ions was conducted and the average lifetime values are calculated. The CIE chromaticity co-ordinates calculated for different excitation routes fall in the reddish orange region of CIE diagram and the same for La_1.98Sm_0.02(MoO₄)₃ nanophosphors are found to be (0.601, 0.394) with a colour purity of 97.21% which disclosed the relevance of La_2−xSm_x (MoO₄)₃ as a potential red phosphor material.