We report the observation of the intrinsic fluorescence of anydrous gadolinium trichloride GdCl3 when laser light is absorbed into the first excited state 6P7/2. With the aid of a frequency doubled pulsed dye laser, we are able to analyze carefully the excitation and emission spectra as well as the decay times over a range of temperatures including that at which the material undergoes a ferromagnetic transition at 2.2 K. At 4.4 K and above, experiments at low excitation density (N0<1014 excited ions/cm3) show that the intrinsic and the impurity induced trap fluorescence dynamics are well described in terms of a fast diffusion and trapping model. When the excitation density is increased anti-Stokes fluorescences appear efficiently; they are assigned to the 6D9/2, 6I7/2→8S7/2 transitions. High excitation density effect on the intrinsic decay as well as the decay of the anti-Stokes fluorescence are nicely reproduced by a theoretical model involving mainly an exciton–exciton annihilation process. Moreover, an excited state absorption mechanism contributes notably to the anti-Stokes fluorescence intensity at t=0 with increasing the excitation density. In the ferromagnetic phase of GdCl3, at 1.5 K, the one-dimensional nature of the exciton diffusion (8S7/2↔6P7/2) is confirmed by the ‘‘incoherent’’ exciton decay analysis using an appropriate model recently developed by Cibert et al. Finally a diffusion length spreading over 2500 visited Gd3+ normal sites is evaluated, knowing the hopping time as a function of the nearest neighbor interactions (nn) in the crude approximation of an ideal two level system in a linear chain of atoms.
We report the observation of a magnon sideband in the 6P7/2 ⇐ 8S7/2 optical absorption spectrum of Gd+3 in the ferromagnetic insulator GdCl3. The transition energy and its dependence on magnetic field demonstrate this to arise from the simultaneous excitation of a magnon and optical exciton. The decrease in its intensity with increasing magnetic field suggest the source of its intensity is directly connected with the zero‐point spin deviations which occur in a ferromagnet possessing significant magnetic dipolar interactions. The magnitude of the intensity is shown to be consistent with a single‐ion transition mechanism which because of the zero‐point spin deviations allows a small probability for a double‐excitation process. This transition mechanism is distinct from that responsible for the previously observed magnon sidebands in the transition‐metal magnetic insulators.
The authors report a detailed analysis of the intensity and polarisation dependence of the 8 S 7/2 to 6 P 7/2 two-photon transition Stark components of Gd 3+ in the concentrated magnetic insulator Gd(OH) 3 under an applied magnetic field (up to 3.5 T) at very low temperature (2 K). The experimental technique consisted of detecting the ultraviolet 6 P 7/2 to 8 S 7/2 one-photon fluorescent emission resulting from two-photon excitation in the 6 P 7/2 states, using a single pulsed dye-laser beam. The standard second-order theory of Axe is shown to fail in explaining the relative intensities of the Stark components. This is especially true in the case of the Delta M=0 transitions for which strong disagreements are observed. It is shown that the introduction of the third-order contribution involving the spin-orbit interaction within the 4f 6 5d states allows the experimental spectra to be reproduced in a correct way. Finally the effects of ion-ion interactions on the two-photon line profiles are discussed.
A comprehensive report and analysis of our observations of numerous parity-allowed direct two-photon transitions within the
4f7 configuration of the
Gd3+ ion is presented. The experimental technique is ultraviolet fluorescence detection following optical excitation with a dye-laser beam. Previous results and analyses are extended in three ways. (1) The intensities and polarization dependence of individual Stark components, in addition to integrated multiplet intensities, are reported and analyzed for
Gd3+:La
F3. In those cases ($^{8}S_{\frac{7}{2}}\ensuremath{\rightarrow}^{6}P_{\frac{5}{2}},^{6}D_{\frac{9}{2},\frac{3}{2},\frac{5}{2}}$) where a second-order theory of two-photon absorption adequately explains the integrated intensity, it also (with the exception of
6D29) explains the Stark-component intensities. The remaining transitions are anomalously strong, and in some cases violate the angular momentum selection rules $\ensuremath{\Delta}L,\ensuremath{\Delta}J\ensuremath{\le}2$ and exhibit strong anisotropies, in contradiction to the second-order theory. It is shown that introduction of third- and fourth-order contributions involving spin-orbit and/or crystal-field interactions among levels of the
4f65d configuration, which serve as intermediate states, can account for both the integrated and Stark-component intensities of these transitions. (2) The strong anisotropy observed for the transitions $^{8}S_{\frac{7}{2}}\ensuremath{\rightarrow}^{6}P_{\frac{3}{2}},^{6}I_{J},^{6}D_{\frac{1}{2}}$ in
Gd3+:La
F3 is explained quantitatively as a polarization-dependent interference between contributions to the intensity which are comparable in magnitude. Interference is destructive for $\stackrel{\ensuremath{\rightarrow}}{E}\ensuremath{\parallel}\stackrel{^}{z}$ and constructive for $\stackrel{\ensuremath{\rightarrow}}{E}\ensuremath{\perp}\stackrel{^}{z}$, creating an order-of-magnitude contrast in the line strength for the two polarizations. (3) A two-photon excitation spectrum of
Gd3+ in aqueous solution is reported. Linewidths comparable to those of room-temperature solids and Stark splittings which suggest a low-symmetry quasistatic environment are observed.
The observation of two-photon absorption by a very efficient up-converted emission is reported for
Ho3+ in Ca
F2, Sr
F2, and Cd
F2 with both cw- and pulse-laser excitations. The two-photon excitation spectra are found to be highly structured and consist of two bands: The band
A is excited by the dye-laser photons of frequencies 15 400-15 700 ${\mathrm{cm}}^{\ensuremath{-}1}$: The band
B is excited by the dye-laser photons of frequencies 15 800-16 400 ${\mathrm{cm}}^{\ensuremath{-}1}$. No one-photon absorption is observed for
Ho3+ in the above lattices at twice these frequencies. Studies of concentration dependence, temperature dependence, and dependence on the pulse repetition rate are used for the assignment of the band. The investigation shows that the two bands
A and
B arise from two different modes of two-photon excitation. The band
A is assigned to arise from a sequential (stepwise) two-photon excitation $^{5}I_{8}\ensuremath{\rightarrow}^{5}F_{5}\ensuremath{\rightarrow}^{5}D_{2}$. The band
B is assigned to arise from the direct two-photon absorption $^{5}I_{8}\ensuremath{\rightarrow}^{3}L_{8}$. Our results are in agreement with the prediction of the Judd-Ofelt theory of lanthanide transition intensities.