SELECT "Researched at" FROM table_4263 WHERE "Geometry" = 'D: ~50nm, L: ~600nm'
Where was d: ~50nm, l: ~600nm geometry researched?
CREATE TABLE table_4263 (
    "Material" text,
    "Type" text,
    "Geometry" text,
    "Output voltage" text,
    "Output power" text,
    "Synthesis" text,
    "Researched at" text
)