Electronic Supplementary information Detailed synthesis of Eu 3+ doped YVO 4 nanoparticles YVO 4 doped with Eu 3+ was synthesized using co-precipitation method. Eu was taken as substitutional dopant in place of Y. In a typical experiment, stoichiometric quantities of precursors Yttrium Oxide (Y 2 O 3 ), Vanadium pentoxide (V 2 O 5 ), Europium oxide (Eu 2 O 3 ) were taken according to chemical formula Y 0.95% VO 4 : (Eu) 0.05% . Oxide precursors were dissolved in minimum amount of HCl

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... All the precursor solutions were mixed ultrasonically and HNO 3 :H 2 O 2 in volume ratio 3:1 was added to the above mixture to convert the precursors to soluble nitrate. NH 4 OH and H 2 O 2 in the volume ratio 3:1 was added drop wise into the solution till the pH of the solution was 10 when ultrafine particles of YVO 4 doped with rare earth ions started forming and were precipitated out in centrifuge. A moderate alkaline pH (10) leads to slow precipitation of Y(OH) 3 which reacts slowly with vanadate ions to produce yttrium orthovanadate. The amount of NH 4 OH present in the solution is very important as it controls the pH and the nucleation rate of the nanocrystals. YVO 4 :Eu NP's were washed with DI water and then with ethanol to dehydrate the surface bound water molecules as OHis a known quencher of luminescence. Finally the precipitates were dried in an oven at 40 0 C for 12 hrs. Detailed synthesis procedure for Silver nanoprisms 1 ml of 5mmol of AgNO 3, 3ml of 15mmol of Poly Vinyl Pyrrolidone were synthesized and added to a coanical flask containing 50 ml of double distilled water. The solution was covered by aluminum foil and left for stirring for 15-20 minutes on a magnetic stirrer. After stirring was complete 3ml of 30mmol Trisodium Citrate (Na 3 C 6 H 5 O 7 ) was added to the solution followed by stirring for 15 minutes. The final solution can be termed as (Solution A) A standard solution of NaBH 4 was made by dissolving 9.5mg of NaBH 4 in 24ml of water. Different quantities of NaBH 4 solution were added with different concentrations of H 2 O 2 solution (30% W/V) to tune the size of silver nanoprisms.