Site-selective Excitation Spectroscopy Research Articles

Eu/RG absorption and excitation spectroscopy in the solid rare gases: State dependence of crystal field splitting and Jahn–Teller coupling

Absorption spectroscopy recorded for annealed samples of matrix-isolated atomic europium reveals a pair of thermally stable sites in Ar and Kr while a single site exists in Xe. Plots of the matrix shifts of the visible s → p bands versus host polarizability, allowed the association of the single site in Xe and the blue sites in Ar and Kr. On the basis of the similar ground state bond lengths expected for the Eu-rare gas (RG) diatomics and the known Na-RG molecules, the blue sites are attributed to Eu occupancy in the smaller tetra-vacancy while the red sites are proposed to arise from hexa-vacancy sites. Both sites are of cubic symmetry, consistent with the pronounced Jahn-Teller structure present on the y(8)P ← a(8)S(7/2) transition for these bands in the three hosts studied. Site-selective excitation spectroscopy has been used to reanalyze complex absorption spectra previously published by Jakob et al. [Phys. Lett. A 57, 67 (1976)] for the near-UV f → d transitions. On the basis that a pair of thermally stable sites exist in solid argon, the occurrence of crystal field splitting has been identified to occur for the J ≥ 5/2 level of the (8)P state when isolated in these two sites with cubic symmetry. From a detailed lineshape analysis, the magnitude of the crystal field splittings on the J = 5/2 level in Ar is found to be 105 and 123 cm(-1) for the red and blue sites, respectively.

Laser site-selective excitation spectroscopy ofEu3+-doped yttrium aluminum garnet

We report the results for laser site selective excitation spectroscopy of ${\mathrm{Eu}}^{3+}$-doped yttrium aluminum garnet. We identified four primary luminescent centers (A--D) from the ${}^{7}{\stackrel{\ensuremath{\rightarrow}}{{F}_{0}}}^{5}{D}_{0}$ excitation spectra and, from the ${}^{5}{\stackrel{\ensuremath{\rightarrow}}{{D}_{0}}}^{7}{F}_{1}$ luminescence spectra, further identified five, two, four, and two secondary centers, respectively, within these primary A--D centers. From a detailed investigation of their spectroscopic properties that specifically include the ${}^{5}{D}_{0}$ energy ${(E}_{0}),$ the ${}^{5}{D}_{0}$ lifetime $({\ensuremath{\tau}}_{0}),$ and the crystal-field strength ${(S}_{k},k=2,4,6),$ we found trends of ${E}_{0}$ in ${E}_{0}(\mathrm{A})$ $<{E}_{0}(\mathrm{B})$ $<{E}_{0}(\mathrm{C})$$<{E}_{0}(\mathrm{D}),$ ${\ensuremath{\tau}}_{0}$ in ${\ensuremath{\tau}}_{0}(\mathrm{A})$$>{\ensuremath{\tau}}_{0}(\mathrm{B})$ $>{\ensuremath{\tau}}_{0}(\mathrm{C})$$>{\ensuremath{\tau}}_{0}(\mathrm{D}),$ and ${S}_{2}$ in ${S}_{2}(\mathrm{A})$ $<{S}_{2}(\mathrm{B})$ $<{S}_{2}(\mathrm{C})$ $<{S}_{2}(\mathrm{D}).$ Local structures of the four primary ${\mathrm{Eu}}^{3+}$ centers were proposed. The A center is attributed to regular, unperturbed ${\mathrm{Eu}}^{3+}(c)$ ions and the other three B--D centers are attributed to ${\mathrm{Eu}}^{3+}(c)$ ions perturbed by the next-nearest neighbor ${\mathrm{Y}}^{3+}(a)$ ions that are created by a site exchange between ${\mathrm{Y}}^{3+}(c)$ and ${\mathrm{Al}}^{3+}(a)$ cations during crystal growing. The secondary centers' local structures were also proposed. They form due to a further perturbation of the next-nearest neighbor ${\mathrm{Eu}}^{3+}(c)$ or ${\mathrm{Al}}^{3+}(c)$ ions on each of the primary centers.

Laser properties of Nd3+ in K5Nd(MoO4)4 stoichiometric disordered crystal

Abstract The spectroscopic and laser properties of K5Nd(MoO4)4 crystal have been thoroughly investigated to show the relationship between the optical properties of Nd3+ ions and the crystal structure. High-resolution site-selective excitation spectroscopy performed at low temperature has demonstrated the existence of two broad crystal field site distributions for Nd3+. In agreement with this result, a broad laser emission has been observed. The shape and width of the laser line strongly depend on the polarization of the pump pulse. The temporal evolution of the laser spectrum shows remarkable changes in its spectral structure.

Photoluminescence fromSi/SiO2single quantum wells by selective excitation

We have studied the photoluminescence (PL) mechanism of crystalline Si single quantum wells sandwiched between ${\mathrm{SiO}}_{2}$ layers by site-selective excitation spectroscopy. The asymmetric PL spectrum is observed in the red spectral region at low temperatures and can be divided into two PL bands. The peak energy of the strong PL band is almost independent of the well thickness and appears near $\ensuremath{\sim}1.65\mathrm{eV}.$ Under selective excitation at energies within the weak PL band, TO-phonon structures are observed in both PL and PL polarization spectra. Steplike TO-phonon structure in the PL spectrum of two-dimensional Si quantum wells is similar to that of zero-dimensional Si nanocrystals. The PL properties of very thin Si quantum wells are discussed.

Photoluminescence mechanism in surface-oxidized silicon nanocrystals

We have studied photoluminescence (PL) properties of surface-oxidized Si nanocrystals fabricated with a ${\mathrm{SiH}}_{4}$ plasma cell. The size dependence of the PL spectrum, the PL decay dynamics, and site-selective excitation spectroscopy show that the efficient and broad PL band around \ensuremath{\sim}1.65 eV originates from excitons localized at the interface between crystalline Si and the ${\mathrm{SiO}}_{2}$ surface layer. The PL from the crystalline Si core state in large nanocrystals appears in the infrared spectral region. By comparison between surface-oxidized Si nanocrystals and as-prepared porous Si, the size and surface dependence of the coupling between electronic and vibrational excitations are discussed.

Site selective upconversion in Nd 3+:KLiYF 5

Site selective upconversion of Nd 3+:KLiYF 5 is reported in dilute (0.2% molar) and concentrated (3.4% molar) crystals. On the basis of site selective excitation spectroscopy, the mechanism for upconversion is determined as being due to the sequential absorption of two photons. The excitation spectrum is shown to be composed of features resonant with each of the two stages of excitation. The dilute sample shows site selective upconversion fluorescence throughout the excitation range. For the more concentrated sample, energy transfer amongst the lower states equalises the population of the sites when shelved in the metastable 4 F 3 2 state so that site selectivity only occurs during the second absorption stage.

Universal feature of vibrational modes of disordered materials investigated via optical spectra of doped probe molecules

We have experimentally determined the density of states of low-frequency host vibrational modes (WDOS)_which couple to the electronic states of chromophores embedded in SiO 2 and SiO 2 TiO 2 gels prepared by a sol-gel method and poly(vinyl butyral). Site-selective excitation spectroscopy has been performed at 4K to obtain the fraction of the zero-phonon line intensity without suffering from spectral hole burning effects. By quantitative analysis of the results, the single-site spectrum and the one-phonon function, which is related to WDOS, have been obtained numerically. It has been found that there exists a universal feature in normalized WDOS of chromophore-embedded amorphous solids of various types.

Universality in vibrational modes of various disordered materials examined by hole-burning-free FLN spectroscopy

Site-selective excitation spectroscopy has been performed for various dye-doped disordered materials which tend to suffer from hole-burning. The densities of states for low-frequency vibrational modes of the hosts, weighted by the electron-phonon interaction strength, have been determined and show a universal feature when the scales are normalized.

Site Selective Spectroscopy of ZnS:Tm3+ Crystals

AbstractThe method of site selective excitation spectroscopy is applied to Tm3+ ions in ZnS crystals containing various codopants. By dye‐laser 4f–4f excitation at helium and neon temperatures it is possible to separate three different sites, for which 4f–4f emission, excitation, and absorption spectra are determined in the range of several free‐ion transitions. Energy spectra are deduced from these data, and some considerations are made about the nature of the sites observed.