Silver nanoprisms of different sizes influence fluorescence enhancement in YVO4:Eu(3+) nanoparticles to various degrees under excitation of green light (532 nm). The local field generated by silver nanoprisms and their dimers is simulated through the FDTD method and a direct correlation with fluorescence enhancement is established.

A silver nanoprism (Ag NP) generates a near field due to multipolar surface plasmon resonance (SPR) and lightening rod effects and acts as a multipolar nanoantenna. The ability of Ag NPs to create such an effect even under an infrared (IR) optical field far off of resonance from the SPR frequency is demonstrated through finite difference time domain simulations of exact Ag NPs and hybrids. The conclusive experimental proof of such a near field around Ag NPs under low-intensity (1.5 mW) IR (980 nm) light came when it could excite fluorescence from YVO 4 /Eu 3+ nanoparticles that otherwise do not fluoresce under IR. The results open up new vistas for exclusive plasmonic excitation of fluorescence through metal NP hybrids/ ensembles.

A dual excitation, dual emission phosphor has been fabricated by simultaneous doping of lanthanide ions Er 3+ , Yb 3+ , Eu 3+ in a highly efficient host YVO 4 . YVO 4 doped with Er 3+ , Yb 3+ , Eu 3+ showed dual excitation i.e., simultaneously excitable by UV and IR radiation and dual emission i.e., fluorescence in bright red under UV excitation and intense green under IR excitation. Red DC fluorescence arises due to 5 D 0 -7 F J transitions of Eu 3+ . UC emission spectra indicate that Yb 3+ not only sensitize Er 3+ to emit predominantly in the green but also Eu 3+ to produce signature red emission. A direct assembly of Ag nanoparticles (NPs) and YVO 4 : Er 3+ , Yb 3+ , Eu 3+ on a suitable substrate showed enhancement of fluorescence of Eu 3+ red emission under UV excitation. Such studies indicate that two dimensional conformal transparent layer of Ag NP-phosphor combine on a silicon solar cell may be used as DC and UC solar spectrum converter from UV/IR to visible region where spectral response of Si is high.The UC emission spectra from YVO 4 :Er 3+ ,Yb 3+ , Eu 3+ nanoparticles prepared by CPP method (Fig.4a), showed much weaker red emission from Er 3+ (650-665nm, 4 F 9/2 -4 I 15/2 ) and Eu 3+ UC emission at 615nm ( 5 D 0 -7 F 2 ) and a sharp intense peak at 720nm ( 5 D 0 -7 F 6 ). Since in NPs, Eu 3+ may occupy surface sites without inversion symmetry, 5 D 0 -7 F 6 transition becomes prominent. Considerably less luminescence in NP's is due to inefficient incorporation of high concentration of activators (Er 3+ ,Yb 3+ ) ions near room temperature synthesis. Down conversion luminescenceThe DC emission spectra of YVO 4 : Er 3+ , Yb 3+ , Eu 3+ nano and bulk phosphor material is shown in Figure 3(b). The fluorescence spectrum showed major peaks at 618 nm and 698 nm when excited at 300 nm arising due to 5 D 0 -7 F 2 and 5 D 0 -7 F 4 transitions of Eu 3+ ions occupying Y 3+ sites. The electric dipole transitions of Eu 3+ (ΔJ = ±2, ±4) are hypersensitive to site symmetry and the effect can be seen with very intense 5 D 0 -7 F 2 and 5 D 0 -7 F 4 transitions. It was clearly indicated that under UV excitation, the same sample gives red color emission which confirms the down conversion of the UV wavelength to visible wavelength. The background bright orange red spot shows the actual photograph of YVO 4 : Er 3+ , Yb 3+ , Eu 3+ (SSR) under UV excitation. The photoluminescence excitation (PLE) spectra of YVO 4 :Er 3+ , Yb 3+ , Eu 3+ nanoparticles at 618 nm Eu 3+ emission is shown as inset in Fig.4(b). The spectrum shows a broad band from 250 to 350 nm due to the charge transfer absorption of the VO 4 3in the host YVO 4 and sensitizing the activator Eu 3+ ion. [21] The broad charge transfer band clearly shows the efficient host (YVO 4 ) to imparts the energy to the other Yb 3+ ion that comes back to the ground 2 F 7/2 state. The excited Yb 3+ ion successfully transfer the energy to various ladder like levels of Er 3+ ion from where non radiative relaxation and radiative transition ( 2 H 11/2 → 4 I 15/2 and 4 S 3/2 → 4 I 15/2 )...

Internal optical forces emerging from plasmonic interactions in gold nanodisc, nanocube and nanobar dimers were studied by the finite element method. A direct correlation between the electric-field enhancement and optical forces was found by observing the largest magnitude of optical forces in nanocube dimers. Moreover, further amplification of optical forces was achieved by employing optical power of the excitation source. The strength of optical forces was observed to be governed by the magnitude of polarisation density on the nanoparticles, which can be varied by modifying the nanoparticle geometry and source wavelength. This study allows us to recognise that nanoparticle geometry along with the inter-dimer distance are the most prominent design considerations for optimising optical forces in plasmonic dimers. The findings facilitate the realisation of all-optical modulation in a plasmomechanical nanopillar system, which has promising applications in ultra-sensitive nanomechanical sensing and building reconfigurable metamaterials.