Nanoplasmonics and surface enhanced spectroscopy.

Enhancement of Bi3+ emission in YAG:Bi, Yb samples by plasmon resonance in Ag NPs at low temperature
M. Kushlyk1,2, V. Tsiumra1,2, Ya. Zhydachevskyy1,3, A. Suchocki1
1Institute of Physics PAS, Al. Lotników 32/46, Warsaw 02-668, Poland 
2Ivan Franko National University of Lviv, 79017, 107 Hen. Tarnavskoho Str., Lviv, Ukraine 
3Lviv Polytechnic National University, 12 Bandera, Lviv 79646, Ukraine
Е-mail: kushlykmarik@gmail.com

Recently it was shown that ideal down converting material on surface of Si solar cells allow increasing their efficiency from 30 up to 36% [1]. A lot of systems which have donor UV excitation and acceptor near-infrared emission are known. Main problem of such materials is low quantum efficiency. Combination of thin conversion layer, with silver plasmonic nanostructures leads to increase donor absorption and emission capacity. 
Bi3+ and Yb3+ co-doped YAG phosphorescent films on YAG crystals surface were prepared by liquid-phase epitaxy. Ag nanostructures, SiO2 spacer and passivation layers were deposited by a magnetron-sputtering technique. The nucleation and growth of Ag nanoparticles were controlled by a thermal annealing process. Two absorption bands in a region from 340 to 380 nm and from 440 to 550 nm caused by quadrupole and dipole modes of surface plasmon resonance (SPR) of Ag NPs respectively were observed. At low temperature, quadrupole mode of SPR shifts towards lower energies. Bi3+ emission increasing is achieved only in case of large (d>50nm) Ag-NPs on YAG:Bi,Yb surface and low temperatures.
High enhancement factors are caused by a close matching of the maximum of plasmon extinction and Bi3+ emission bands. The enhancement in PL intensity can be explained by the interaction between the spontaneous recombination and surface plasmon in metal nanoparticles.

Acknowledgements: The work was supported by the Polish National Science Center (project 2015/17/B/ST5/01658).

1.	T. Trupke and M. A. Green  Improving solar cell efficiencies by down-conversion of high-energy photons // Journal of Applied Physics.-2002.-92, N 3.-P. 1668-1674.