Intense red emitting monoclinic LaPO4:Eu3+ nanoparticles: host-dopant energy transfer dynamics and photoluminescence properties

• Main Authors: Gupta, Santosh K, Ghosh, P. S, Sahu, M, Bhattacharyya, K, Tewari, R, Natarajan, V
• Format: Article
• Language: English
• ISSN: 2046-2069
• DOI: 10.1039/c5ra09076h

LaPO 4 nanoparticles were synthesized using complex polymerization method and characterized systematically using X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. Varied concentration of europium ion is doped in the LaPO 4 lattice and optical properties and Judd-Ofelt analysis were investigated. It is observed that LaPO 4 nanoparticles give violet-blue emission when irradiated with UV light. On doping europium ion the band gap of LaPO 4 decreases. Based on DFT calculations it is proposed that energy range over which d and f states of Eu are distributed is coincident with the valence band of LaPO 4 so causing an efficient energy transfer from LaPO 4 to europium ion. The actual site symmetry for europium ion in lanthanum orthophosphate was also evaluated as D 2d based on the Stark splitting pattern although it is C 1 for La 3+ in LaPO 4 . The critical energy-transfer distance for the Eu 3+ ions was evaluated, based on which the quenching mechanism was verified to be an electric multipolar interaction. It is also observed that the red emission intensity of LaPO 4 :Eu 3+ (2.0 mol%) is almost 85% of a commercial red phosphor, which clearly demonstrates that the as-prepared samples are promising red phosphors under near-UV for use in white-light emitting diodes. Visible host emission and dynamics of host-dopant energy transfer in LaPO 4 :Eu phosphor is investigated using PL and complimented by DFT.