Two dimensional nanophosphors of high quality play an important role in the miniaturization and intelligentization of opto-electronic components. In this present work, ultra-large (30μm) single crystals of (Y0.95Eu0.05)2(OH)5NO3·nH2O layered rare earth hydroxide (LRH) with a hexagonal shape have been synthisized via autoclaving the rare-earth nitrate/NH4OH reaction system in the presence of ammonium nitrate (NH4NO3). The nitrate ions, existing in the interlayer gallery of layered rare earth hydroxide, exhibit facile exchanges with oleate anions by hydrothermal anion exchange. Furthermore, the interlayer distance can thus be expanded from ~0.9 nm for the pristine LRHs to ~3.60 nm for the intercalated ones, which are then efficiently delaminated into unilamellar nanosheets with a lateral size of 10μm and a thickness of ~1.50 nm. The obtained nanosheets are single crystaline. Highly [11 oriented, dense (Y0.95Eu0.05)2O3 phosphor films with excellent optical transparency and a greatly enhanced luminescence intensity have been constructed via self-assembly of ultra-large unilamellar LRH nanosheets, followed by proper annealing.