The scintillation intensity and decay from Nd³⁺4f²5d and 4f³excited states in several fluoride crystals

Abstract

Nd3+-doped LaF3, LiYF4, CsY2F7, BaY2F8 and BaF2 crystals were investigated. For scintillator applications, the characteristics of the fast Nd3+ 4f25d to 4f3 emission component is of interest. The effective 4f25d to 4f3 scintillation decay time under gamma irradiation was found to vary from 5 to 42 ns, depending on the host lattice. Light yields were determined under X-ray excitation. The 4f25d to 4f3 output from many samples was seriously affected by impurity absorptions. After correcting for these, an estimate was made of the maximum possible 4f25d to 4f3 light yield to be expected in very pure Nd3+-doped crystals. In neither of the cases was a 4f25d to 4f3 light yield of more than about 1000 photons per MeV of X-ray energy found. In addition to Nd3+ 4f25d to 4f3 emission, Nd3+ 4f3 to 4f3 and host emissions were also recorded at wavelengths shorter than 550 nm. A semi-quantitative model is given for the Nd3+ 4f25d to 4f3, 4f3 to 4f3 and host emission intensities.

Concentration dependence study of VUV–UV–visible luminescence of Nd3+ and Gd3+ in LuLiF4

“…Fast scintillators emitting in VUV spectral region can be coupled with position-sensitive detectors filled with photosensitive gases or with other VUV-sensitive detectors and used in special imaging techniques [1]. Wide band-gap fluorides are the best single crystal host for this purpose, and the Nd 3+ ion provides fast 5d-4f emission around 180-190 nm in the host lattices like LaF 3 , LiYF 4 , LuLiF 4 , BaY 2 F 8 and others [2][3][4], while the oxide hosts are not suitable for this purpose due to the overlap of the lowest lying 5d levels with the 4f ones [5]. High energy shifted Nd 3+ emission, i.e.…”

VUV Laser Spectroscopy of Trivalent Rare-Earth Ions in Wide Band Gap Fluoride Crystals

“…When the spin and the spatial parts of the wave functions are coupled within the framework of the symmetry group of the RE ion, the number of the energy levels is described by the decomposition of the product representation of Γ (6) (spin part) with Γ (4) , Γ (5) , Γ <3) , and Γ ω . The new energy levels now are the following:…”

“…When the crystal field of trigonal symmetry is applied, on the 4 K W2 level of the Nd 3+ free ion, it splits it into three Stark components: 2(Γ (4) + Γ (5) + Γ (6) ), Γ (4) , Γ (4) (6) ). Some of these components are degenerate and the degeneracy is removed within the 4f 2 5d electronic configura tion.…”

“…The first method uses VUV lasers [4] and/or x-ray or synchrotron radiation [5,6]. This pumping arrangement has the advantage of populating the levels of the 4f "~'5d electronic configuration directly from the ground state of the trivalent RE ion, via one photon transition only.…”

“…However, there are problems related to the design of the optical projection sys tem, due to the fact that the absorption coefficient of most materials in the VUV is large, yet, their optical properties degrade constantly with time under VUV irradiation. Up to now, only calcium fluoride seems to be promising as optical material for 157 nm photolithography, and the possibility of using wide band gap fluoride dielectric crystals, such as YF 4 and LiCaAlF 6 , as optical elements for 157 nm photolithography was investigated. These materials could be grown from melts at lower temperature than CaF 2 and they have similar physical proper ties, despite the fact that they are forming crystals of different symmetry than cubic.…”