Deciphering the site occupancy and photoluminescence character of Sm3+ in dense-packed Ca3MgSi2O8 nanocrystals using time-resolved emission spectroscopy

Photoluminescence properties of a series of Sm+3 doped ternary alkaline earth silicate phosphor: Ca3-xMgSi2O8: xSm(+3), synthesized by sol-gel method, were investigated. The crystal structure of the prepared phosphors was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transforms infrared (FTIR) spectroscopy. The phosphor crystallized into a monoclinic crystal system in P121/a1 space group as a pure single-phase nano-powder. Rietveld refinement results elucidate the presence two coordination sites for Ca2+ ions in the lattice and both can be replaced with Sm3+ upon doping. Among the several excitation peaks observed in the UV region, (6)H5/2 -> (4)F7/2 (404 nm) transition was most prominent. The emission profile was comprised of four bands centring at 563, 600, 647, and 707 nm and among them (4)G5/2 -> 6H7/ 2 (600 nm) was the dominant transition. Luminescence quenching appeared beyond the optimum doping concentration of 2 mol %. The exchange mechanism responsible for the concentration quenching was primarily associated with quadrupole-quadrupole interactions. The luminescence demonstrated mono-exponential decay below 0.25 mol% and bi-exponential decay above 0.5 mol% Sm3+ concentration. The observed bi-exponential decay could be attributed to the samarium luminescence from two different coordination sites. The presence of the isoemissive point in the time resolved area normalised emission spectra (TRANES) confirmed the existence of two distinct luminescent centres in the samarium doped Ca3MgSi2O8. Analysis of decay amplitudes validated the TRANES observation and ascribed the origin of fast and slow components of the bi-exponential decay to emission from Sm3+ ions occupied at two distinct Ca sites. The luminescence lifetime (tau(av) = 2.13 ms), quantum yield (57.36%) and chromaticity parameters indicated that Ca3-xMgSi2O8:xSm(+3) can be a promising phosphor for the red spectral component in nUV- wLED application.

Automated summary

The photoluminescence properties of Sm+3 doped ternary alkaline earth silicate phosphor Ca3-xMgSi2O8: xSm(+3) synthesized by sol-gel method were studied. The crystal structure of the phosphor was characterized by XRD, SEM, and FTIR spectroscopy. The emission spectrum consisted of four bands, with luminescence quenching observed beyond the optimal doping concentration, primarily due to quadrupole-quadrupole interactions.