Van Thanh, NguyenNguyenVan ThanhTUAN HUNG NGUYENTakehara, HikaruHikaruTakeharaTaguchi, AtsushiAtsushiTaguchiYi, HsinHsinYiSolís-Fernández, PabloPabloSolís-FernándezAgo, HirokiHirokiAgoYang, PengfeiPengfeiYangLi, Lain-JongLain-JongLiLizárraga, KevinKevinLizárragaSaito, RiichiroRiichiroSaitoLiu, Hsiang-LinHsiang-LinLiu2026-01-082026-01-082025-07-07https://www.scopus.com/record/display.uri?eid=2-s2.0-105022976144&origin=resultslisthttps://scholars.lib.ntu.edu.tw/handle/123456789/735144We report the excitonic properties of hexagonal boron-nitride (h-BN) thin films as a function of thickness using deep-ultraviolet photoluminescence spectroscopy and spectroscopic ellipsometry for optical absorption analysis. The peak positions of the defect-induced donor-acceptor PL emissions and the band-to-band exciton absorption exhibit a blueshift with increasing thickness or an increase in the effective dielectric constant of the surrounding environment. The optical absorption spectra analyzed using the Elliott model, combined with renormalized band-gap calculations, reveal an exciton binding energy of 1.04 eV for monolayer h-BN, which decreases to 0.16 eV in h-BN single crystal due to environmental screening effects on the electron-hole interactions. Furthermore, both the band-gap value and Urbach energy decrease as the film thickness increases. The optical absorption coefficient derived from spectroscopic ellipsometry measurement of monolayer h-BN is directly compared with results from the first-principles GW plus Bethe-Salpeter equation calculations.falsejournal article10.1103/231t-g3mn2-s2.0-105022976144