Study of UV fluorescences induced from 4f3 T 4f25d multistep absorptions of Nd3+ions in YLiF4 and LuLiF4 crystals

Abstract

Nd3+ ultraviolet (UV) fl uorescence induced by multiphotonic laser excitations was studied in doped Nd:YLiF4 (YLF) and Nd:LuLiF4 (LLF) crystals by using the time resolved spectroscopy technique. The UV luminescences are due to transitions between the 4f25d and the 4f3 electronic confi gurations of Nd3+ ions. The 4f25d confi guration can be reached by direct pumping or by multiphotonic excitation, both processes give rise to the UV band emission with structure due to the strong phonon coupling expected for 5d orbital involvement in the transition. The multiphotonic excitation process is due to three photons (532 nanometers [nm]) sequential absorptions by metastable levels of the 4f3 confi guration split by crystalline local fi eld. The sequential excitation of Nd by the laser excitation is attributed to the 4I9/2 + 532 nm T 4G7/2 ground state absorption followed by the 4G7/2 + 532 nm T 2F5/2 and 2F5/2 + 532 nm T 4f25d excited state absorptions. The UV emissions due to 4f25d confi guration are parity allowed, having lifetime of 35 nanoseconds (ns) in contrast to UV emissions from 4f3 confi guration which are induced by two absorption steps and are parity forbidden showing longer lifetime of 8 microseconds (ms) and narrow lines. The polarization effects of the UV emissions were studied and their behaviors are dependent on the excited state confi guration involving or not involving the 5d orbital. The allowed UV emission positions were affected by the host variation more than the ones originated from the 4f3 confi guration as expected. The electronic energy of the 4f25d confi guration shifts to lower energy for increasing the crystal fi eld.