Search

The phenomenon of photon avalanche, which involves both an excited state absorption process from a metastable level and a cross relaxation energy transfer process responsible for the large increases in population of this metastable level, has been investigated in ${\mathrm{LaCl}}_{3}:{\mathrm{Pr}}^{3+}.$ In this paper, we report on the intensity dependence of both the steady-state fluorescence and the temporal evolution of the avalanche signal as a function of temperature (80 K to room temperature). Comparisons are made between experimental results and mathematical models based on a six-level system described by a series of coupled rate equations combined with the propagation of a Gaussian beam. We develop a model with only one adjustable parameter, the excited state absorption cross section, which provides a good description of all of our experimental data. We have estimated values of the excited state absorption cross section for the various ${}^{3}{\stackrel{\ensuremath{\rightarrow}}{{\mathrm{H}}_{5}}}^{3}{\mathrm{P}}_{0}$ pumping transitions at different temperatures.

We have investigated the decay of nonequilibrium phonons in LiYF 4 :Pr 3+ (1 at. %) at a temperature of 9.5 K. Nonequilibrium phonon populations at 51.9, 66.0, and 113 cm -1 are generated monochromatically with a high-power pulsed far-infrared laser via defect-induced one-phonon absorption, and their temporal and spectral evolution detected using anti-Stokes absorption. We observe the broadband distribution that results from the anharmonic decay of the initial monochromatic phonon population

We have used photothermal-beam-deflection spectroscopy to measure the change in the index of refraction of ${\mathrm{Ti}}^{3+}$-doped sapphire after pulsed excitation at 532 nm with a neodymium-doped yttrium aluminum garnet laser. The beam-deflection signal arises from both thermal and nonthermal sources. The nonthermal part of the signal decays with the fluorescence lifetime of ${\mathrm{Ti}}^{3+}$ in sapphire. The shape of the nonthermal part depends on whether the probe beam is polarized perpendicular (\ensuremath{\sigma}) or parallel (\ensuremath{\pi}) to the c axis of the crystal. This behavior can be explained by a photoelastic law based upon the anisotropic volume expansion caused by a strong Jahn-Teller effect of the ${\mathrm{TiO}}_{6}$ complex in the excited state. The experimental values of the change in the index of refraction for each ion per unit volume are \ensuremath{\Delta}n/N=3.3 A${\mathrm{\r{}}}^{3}$ and \ensuremath{\Delta}n/N=1.2 A${\mathrm{\r{}}}^{3}$ for \ensuremath{\sigma} and \ensuremath{\pi} polarization, respectively, compared with the calculated values of \ensuremath{\Delta}n/N=3.73 A${\mathrm{\r{}}}^{3}$ (for \ensuremath{\sigma}) and \ensuremath{\Delta}n/N=1.50 A${\mathrm{\r{}}}^{3}$ (for \ensuremath{\pi}) for a model that includes the photoelastic law. The bulk expansion per ${\mathrm{TiO}}_{6}$ complex, derived from the beam-deflection signal, is \ensuremath{\approxeq}11.8 A${\mathrm{\r{}}}^{3}$, while the calculated value based on the configuration-coordinate model is \ensuremath{\approxeq}9.9 A${\mathrm{\r{}}}^{3}$.

We present results of EPR and near-infrared fluorescence-line-narrowing experiments performed on Cr-doped forsterite. The optical measurements permit identification of the signals in the complex EPR spectrum due to the near-infrared lasing center. The site symmetry of the lasing center is shown to be ${\mathit{c}}_{\mathit{s}}$, with the mirror plane being in the crystallographic a-b plane. The magnetic z axes of the two magnetically inequivalent sites are in the mirror plane at an angle of \ifmmode\pm\else\textpm\fi{}43\ifmmode^\circ\else\textdegree\fi{} to the b axis. In addition, the relative energies of the ground-state triplet have also been measured and can be written in terms of spin Hamiltonian energy parameters: D=+2.20 and E=-0.149 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$.

We have investigated the spectral and temporal dynamics associated with phonon decay in the YAG:Pr3+ system at a range of temperature between 9 and 25 K. Nonequilibrium phonons were generated using defect induced one phonon absorption (DlOPA) of far infrared (FIR) radiation. Phonon detection was achieved optically using a variation of absorption vibronic sideband phonon spectroscopy. Far infrared radiation in the frequency range 30 - 113 cm-1 was generated using a transversely excited atmospheric pressure CO2 laser pumped superradiant cell. This configuration produces 50 ns FIR pulses with single pulse energies in the range 1 - 10 mJ. The optical detection pulses were generated using a YAG:Nd3+ pumped dye laser. The generation and detection beams were incident on the sample in a counterpropagating geometry with the phonon generated fluorescence collected at 90 deg. The sample was mounted in a two stage cold cycle refrigerator allowing the temperature to be varied between 9 and 300 K. The sample temperature was determined optically

A study of the decay curves of the $^{1}$${\mathit{T}}_{2\mathit{g}}$${\ensuremath{\rightarrow}}^{3}$${\mathit{A}}_{2\mathit{g}}$ luminescence of ${\mathrm{Ni}}^{2+}$:MgO at two different concentrations of ${\mathrm{Ni}}^{2+}$ (0.11 and 0.25 at. %) reveals a single exponential decay for the 0.11 at. % crystal and non-single-exponential decay for the 0.25 at. % crystal. This is interpreted in terms of transfer of excitation energy by cross relaxation. Fits of the nonexponential decay are most consistent with a dipole-quadrupole mechanism being responsible for the energy transfer. Examination of the oscillator strengths of the relevant ${\mathrm{Ni}}^{2+}$ transitions appears to support this notion, although the presence of an exchange interaction cannot be ruled out. Separate measurements on the $^{3}$${\mathit{T}}_{2\mathit{g}}$${\ensuremath{\rightarrow}}^{3}$${\mathit{A}}_{2\mathit{g}}$ luminescence show that energy transfer from single ions to pairs also takes place. Two different types of ${\mathrm{Ni}}^{2+\mathrm{\ensuremath{-}}}$${\mathrm{Ni}}^{2+}$ pairs are identified, nearest-neighbor ferromagnetic pairs with 2J=2.5 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and next-nearest-neighbor antiferromagnetic pairs with 2J=-35 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$.

Fluorescence and site-selective excitation spectra of chromium-activated forsterite at 10 K are reported. It is found that a high-field ${\mathrm{Cr}}^{3+}$ site in inversion symmetry emits sharp ${\mathit{R}}_{1}$ line fluorescence, while a low field ${\mathrm{Cr}}^{3+}$ site in mirror symmetry produces $^{4}$${\mathit{T}}_{2}$ broadband emission. The dominant absorption in the visible is shown to be the $^{3}$${\mathit{A}}_{2}$${\ensuremath{\rightarrow}}^{3}$${\mathit{T}}_{1}$${(}^{3}$F) transitions of ${\mathrm{Cr}}^{4+}$ in tetrahedral sites. In the near-infrared region, three sharp lines from ${\mathrm{Cr}}^{4+}$ were observed and are assigned to the transition from the $^{3}$${\mathit{A}}_{1}$${(}^{3}$${\mathit{T}}_{2}$) spin triplet to the $^{3}$${\mathit{A}}_{2}$ ground state. The energy-level splittings of ${\mathrm{Cr}}^{4+}$ due to an orthorhombic-distorted field with spin-orbit coupling are discussed.

Le plus bas niveau de Stark de l'etat fondamental de Er 3+ est utilise comme detecteur de phonon et magnon de 36 cm −1 dans un schema de compteur quantique. On utilise un simple ensemble d'equations de rapports pour modeliser le systeme. Determination du temps de declin des phonons et des magnons. Analyse des mecanismes possibles du declin des magnons

Excitation spectra and lifetime measurements were used to distinguish high-field-site (HFS) and low-field-site (LFS) Cr{sup 3+}-ion behaviors. A theoretical analysis of site distribution gives an adequate fit to the luminescent spectra. The residual content of LFS in the glass ceramic was found to depend on the extent of the heat treatment.

Fine spectral structure has been observed in both fluorescence and excitation spectra of ${\mathrm{Cr}}^{3+}$:${\mathrm{LiNbO}}_{3}$ on the high-energy side of the broadband emission from $^{4}$${\mathit{T}}_{2}$ at 10 K. The lifetimes of the structures are found to be much longer than the lifetime of the broadband $^{4}$${\mathit{T}}_{2}$ fluorescence. These sharp lines are assigned to the $^{2}$E${\ensuremath{\rightarrow}}^{4}$${\mathit{A}}_{2}$ emissions (R lines) from two types of ${\mathrm{Cr}}^{3+}$ sites arising from charge compensation; ${\mathrm{Cr}}^{3+}$ ions are found to substitute both for ${\mathrm{Li}}^{+}$ and for ${\mathrm{Nb}}^{5+}$ sites and to form dimerlike pairs.

Presentation d'une technique basee sur la saturation, destinee a isoler et decoupler les composantes individuelles des spectres inhomogenement elargis, qui sont simultanement couplees les unes aux autres par les interactions de recouvrement spectral et de transfert d'energie. Ladite technique est denommee spectroscopie de fluorescence a saturation resolue. On demontre son utilite en deconvoluant les spectres complexes d'une ceramique dopee au chrome

The energies of the $5d$ excited states of ${\mathrm{Ce}}^{3+}$ and ${\mathrm{Pr}}^{3+}$ impurities relative to the conduction band of the insulators ${\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$ and ${\mathrm{Lu}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$ were investigated through a temperature and spectrally resolved photoconductivity study. The effective ionization barrier of ${\mathrm{Pr}}^{3+}$ from the $5d$ state to the conduction band is found to be $0.15\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ smaller than that of ${\mathrm{Ce}}^{3+}$ in both ${\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$ and ${\mathrm{Lu}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$. The difference is explained by a model, represented by rate equations, that takes into account interconfigurational $4f5d\ensuremath{\rightarrow}4{f}^{2}$ relaxation for ${\mathrm{Pr}}^{3+}$, a process that is absent for ${\mathrm{Ce}}^{3+}$.

${\mathrm{Ce}}^{3+}$ and ${\mathrm{Tb}}^{3+}$ singly doped and codoped $\mathrm{Ca}{\mathrm{Al}}_{4}{\mathrm{O}}_{7}$ and ${\mathrm{Y}}_{2}{\mathrm{O}}_{3}$ single crystal fibers were grown using the laser heated pedestal growth method. Energy transfer from ${\mathrm{Ce}}^{3+}$ to ${\mathrm{Tb}}^{3+}$ was studied in these samples. No energy transfer between ${\mathrm{Ce}}^{3+}$ and ${\mathrm{Tb}}^{3+}$ was observed in codoped ${\mathrm{Y}}_{2}{\mathrm{O}}_{3}$. This is because electrons excited into the ${\mathrm{Ce}}^{3+}\phantom{\rule{0.3em}{0ex}}5d$ states delocalize into the conduction band at a rate that is faster than the interionic energy transfer rate, whereas the converse is the case for $\mathrm{Ca}{\mathrm{Al}}_{4}{\mathrm{O}}_{7}$ doped with ${\mathrm{Ce}}^{3+}\phantom{\rule{0.3em}{0ex}}(1\phantom{\rule{0.3em}{0ex}}\mathrm{at}\phantom{\rule{0.2em}{0ex}}%)$ and ${\mathrm{Tb}}^{3+}\phantom{\rule{0.3em}{0ex}}(1\phantom{\rule{0.3em}{0ex}}\mathrm{at}\phantom{\rule{0.2em}{0ex}}%)$. The energy transfer rate was determined to be on the order of ${10}^{9}\phantom{\rule{0.3em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. The transfer occurs before the excited electrons can be thermally promoted into the conduction band. From these results, it can be inferred that the thermal ionization rate $({W}_{\mathit{Th}})$ from the lowest $5d$ excited ${\mathrm{Ce}}^{3+}$ state at $355\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ is less than ${10}^{9}\phantom{\rule{0.3em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ at room temperature, whereas the delocalization rate $({W}_{D})$ into the conduction band is faster than this rate. The location of the ${\mathrm{Tb}}^{3+}$ and ${\mathrm{Ce}}^{3+}$ states relative to the valence and conduction band of these two materials has been determined through photoconductivity measurements.

The relaxation between closely spaced (separation \ensuremath{\sim}10 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) electronic levels of rare-earth ions doped in insulating nanocrystals (size 10--25 nm) embedded in glass is studied by time-resolved fluorescence and fluorescence line narrowing techniques. For particle sizes below 25 nm the relaxation rate increases with a decrease in particle size. The increased relaxation rate is explained by the interaction of the electronic states of rare-earth ions in nanocrystals with the vibrational excitations of the surrounding glass medium and with mixed vibrational modes of the nanocrystallites and the glass. The possibility for the use of rare-earth doped nanocrystals as a probe of the dynamical processes in glass is discussed.

The location of the ground state of ${\mathrm{Er}}^{3+}$ in a ${\mathrm{Y}}_{2}{\mathrm{O}}_{3}$ single-crystal fiber is determined using two-step photoconductivity. The ground state of ${\mathrm{Er}}^{3+}$ ${(}^{4}{I}_{15/2})$ is located 1.0 eV (\ifmmode\pm\else\textpm\fi{}0.3 eV) below the top of the valence band. The second step photocurrent results from excitation of a $4f$ electron from the ${}^{4}{S}_{3/2}$ excited state to the $5d$ state followed by photoionization into the conduction band.

Application of pressure to the nonemitting system ${\mathrm{Lu}}_{2}{\mathrm{O}}_{3}:{\mathrm{Ce}}^{3+}$ leads to the generation of luminescence in the visible. The luminescence is assigned to the $5\stackrel{\ensuremath{\rightarrow}}{d}4f$ transition of ${\mathrm{Ce}}^{3+},$ and is attributed to a pressure-induced electronic crossover of the excited $5d$ state of ${\mathrm{Ce}}^{3+}$ and the conduction-band edge of ${\mathrm{Lu}}_{2}{\mathrm{O}}_{3}.$ The results yield insight into the emission efficiency of $5\stackrel{\ensuremath{\rightarrow}}{d}4f$ transitions, and provide a foundation for advancing new phosphors and tunable laser materials in the visible and ultraviolet based on the broad $5\stackrel{\ensuremath{\rightarrow}}{d}4f$ emission of lanthanides.

The low-temperature homogeneous broadening of the electronic transitions of ${\mathrm{Eu}}^{3+}$ and ${\mathrm{Pr}}^{3+}$ rare-earth impurity ions in ${\mathrm{Y}}_{2}{\mathrm{O}}_{3}$ and ${\mathrm{LaF}}_{3}$ nanocrystals embedded into amorphous materials (polymer and oxyfluoride glass ceramics) was studied with hole-burning and fluorescence line narrowing techniques. It is shown that the homogeneous linewidth is determined by the interaction of the impurity ions contained in the nanocrystals with the two-level systems (TLS's) of the surrounding glass matrix. A comparison of the experiments with a calculation provides direct evidence for the long-range nature of the interaction with the TLS's.

Etude de la relaxation des phonons hors equilibre dans YAG:Pr 3+ (1,0 at.%) a une temperature de 20 K. Les populations des phonons hors equilibre sont generees monochromatiquement avec un laser pulse de forte puissance dont la frequence est situee dans l'infra-rouge lointain en utilisant l'absorption a un phonon induite par les defauts, et leur evolution temporelle et spectrale est determinee en utilisant un spectrometre vibronique a resolution temporelle et a bandes laterales. Deux mecanismes de relaxation dominent: la relaxation anharmonique via les interactions a trois phonons et les processus de diffusion inelastique a un electron et deux phonons

Time-resolved fluorescence line narrowing is used to study spectral energy transfer in Pr${\mathrm{F}}_{3}$ and Pr${\mathrm{Cl}}_{3}$. The excitation spectrum of Pr${\mathrm{F}}_{3}$ in the region of the ${(^{3}H_{4})}_{1}\ensuremath{\rightarrow}^{3}P_{0}$ absorption indicates that several strong satellite lines accompany the main transition, their origin being ascribed to different ${\mathrm{Pr}}^{3+}$ ions lying in strongly perturbed lattice sites. The spectral transfer within the inhomogeneously broadened main transiton is measured, where the energy mismatch is about 2 ${\mathrm{cm}}^{\ensuremath{-}1}$. This process is characterized by a strong ($\ensuremath{\sim}{T}^{4.3}$) dependence of the transfer probability on sample temperature. The growth of the full inhomogeneous emission profile accompanies a uniform decay of the donor line shape. A transfer process between the lowest-energy satellite ions is also measured. Here the energy mismatch is 32 ${\mathrm{cm}}^{\ensuremath{-}1}$ resulting in a weak temperature dependence for the transfer rate. Both the intraline and intersatellite transfer are characterized by simple exponential rate equations. Recent calculations of phonon-assisted transfer probabilities are compared to our measurements, with the intersatellite transfer ascribed to a "one-phonon direct" process whereas the transfer within the main transition occurs by a "one-phonon second-order" mechanism. In Pr${\mathrm{Cl}}_{3}$ the transfer times are faster than the 15-nsec response time of our detection system indicating a much stronger ion-ion coupling.

The electronic transition between the $^{4}T_{1}$ and $^{6}A_{1}$ states of the ${\mathrm{Mn}}^{2+}$ ion in CsMn${\mathrm{Cl}}_{3}$\ifmmode\cdot\else\textperiodcentered\fi{}2${\mathrm{H}}_{2}$O has been observed to be weak compared to the same transition in other hosts, due to vibrational quenching. We have observed fluorescence and infrared-absorption spectra of the deuterated compound CsMn${\mathrm{Cl}}_{3}$\ifmmode\cdot\else\textperiodcentered\fi{}2${\mathrm{D}}_{2}$O and report little change in the phonon sideband associated with the pure electronic transition, but observe a 15-fold increase in the lifetime of the excited state, along with an increase in the $^{4}T_{1}$ luminescence intensity. Infrared spectra reveal an intense band of high-frequency phonons which exhibits a large shift in energy with isotopic substitution. We show that these data are consistent with the theory of multiphonon transitions recently presented by Huang and Gu.

When excited by the 6471-\AA{} line from a krypton laser, blue and uv fluorescence has been observed in La${\mathrm{F}}_{3}$: ${\mathrm{Tm}}^{3+}$ at room temperature. The main emission features have been identified as originating from the $^{1}D_{2}$ and $^{1}G_{4}$ levels, reached by a stepwise excitation process. A set of accurate Judd-Ofelt $\ensuremath{\Omega}$ parameters for La${\mathrm{F}}_{3}$: ${\mathrm{Tm}}^{3+}$ has been derived from the measured lifetime of the $^{1}D_{2}$, $^{1}G_{4}$, $^{3}H_{4}$, and $^{3}F_{4}$ levels.

Laser-induced fluorescence-line-narrowing techniques are extended to measure site-to-site variations in the spectroscopic properties of excited states of optically active ions in glass. The crystalline Stark splitting associated with the initia excited state, rather than the terminal fluorescence state, is observed. The process is illustrated for ${\mathrm{Eu}}^{3+}$ in a lithium-borate glass by exciting the $^{5}D_{1}$ state and observing $^{5}D_{0}\ensuremath{\rightarrow}^{7}F_{J}$ fluorescence. The measured crystal-field splitting of $^{5}D_{1}$ is in good agreement with that predicted from the splitting of $^{7}F_{1}$. Conditions necessary for obtaining fluorescence line narrowing in excited states are discussed.

Etude de la dynamique spectrale donneur-donneur et donneur-accepteur dans le materiau laser La 1−x P 5 O 14 :Nd x 3+ par une methode de fluorescence a resolution temporelle. Explication des resultats experimentaux au moyen d'un modele de Inokuti-Hirayama generalise. Les resultats obtenus a basse temperature et les mesures de diffusion spectrale sont decrits de facon coherente par des modeles de transfert d'energie assiste par phonons, dans lesquels l'excitation du donneur est transferee entre ions isoles d'une maniere incoherente

We report the first observation of the pure electronic transitions in the $^{4}T_{1}$ state of ${\mathrm{Mn}}^{2+}$ ions in the one-dimensional antiferromagnet CsMn${\mathrm{Cl}}_{3}$ \ifmmode\cdot\else\textperiodcentered\fi{} 2${\mathrm{H}}_{2}$O (CMC) in the absorption, excitation, and fluorescence spectra. Selection rules are analyzed: the exciton transition is electric dipole allowed, the magnon sideband in emission is a single-ion process, and is both electric and magnetic dipole allowed; however, the magnon sideband in absorption is an ion-pair process and is a weakened-electric-dipole and magnetic-dipole transition. The density of magnon states and the line profile of the magnon sideband have been calculated. The results explain the peculiar line shapes of the observed sideband emission. An exponential decay of the exciton is observed with a lifetime of 0.57 ms.

The ultraviolet absorption bands of trivalent rare earths in La${\mathrm{F}}_{3}$ are located by the use of absorption and selective excitation spectra. These absorptions are quite strong arising from the electric dipole transition, which promotes a $4f$ electron from the rare-earth $4{f}^{n}$ shell to the $5d$ or some higher-lying orbital. The onsets of the $5d$ absorptions range from about 40 000 ${\mathrm{cm}}^{\ensuremath{-}1}$ for cerium to beyond 80 000 ${\mathrm{cm}}^{\ensuremath{-}1}$ for lutetium showing a general increase from cerium to gadolinium, a sudden drop from gadolinium to terbium, and another increase. The positions of the bands are compared with estimates by several workers of the $5d$ level position for trivalent free ions. In general the La${\mathrm{F}}_{3}$ crystal field lowers and broadens the $5d$ level with respect to its freeion counterpart. For the simplest rare earth, cerium, the splitting caused by the La${\mathrm{F}}_{3}$ crystal field is calculated using a point-charge model. Agreement with experiment is poor, so a two-parameter fit to the splitting is made which indicates that the point-charge model plus the approximation for the radial integrals involved overestimate the crystal-field perturbation on the $5d$ electron by roughly a factor of 3.

We have used time-resolved fluorescence line narrowing to study energy transfer among ${\mathrm{Yb}}^{3+}$ ions in a silicate glass as a function of energy mismatch between donors and acceptors and temperature from 4.2 to 51 K. The observed spectra are consistent with a one-phonon-assisted multipolar interaction between ${\mathrm{Yb}}^{3+}$ ions with a variation with site separation of ${r}^{\mathrm{\ensuremath{-}}13}$. These results are compared to that reported for other rare-earth-ion transitions in glasses and crystals.

Fluorescence-line-narrowing and time-resolved studies have been conducted in ruby crystals and powders, in concentrations varying from 0.025 to 0.9 at.%. The resonance fluorescence component of the ${R}_{1}$ line at low temperatures is observed to increase dramatically as the laser is tuned from line center toward the low-energy wing of the inhomogeneously broadened absorption. This is presumed to indicate the presence of weakly coupled pairs in the wings of the line. Intraline and interline (${R}_{1}\ensuremath{\rightarrow}{N}_{1,2}$) energy transfer have also been studied, and an elaboration of earlier work is given. Time-resolved selective-excitation scans have revealed numerous channels in the vicinity of the $R$ lines by which the different pairs can be directly excited. These are assumed to be Cr ions near enough to a pair to be in a highly perturbed environment. Various experimental results are shown to be consistent with a model of rapid transfer between resonant Cr ions which feeds the pairs via a weak, nonresonant coupling to these perturbed ions. Macroscopic strain broadening is also shown to be favored over microscopic broadening, and the implications for Anderson localization in ruby are discussed.

In this article we present results of optical and ESR studies that have allowed us to study the behavior of ${\mathrm{Cr}}^{3+}$ at disordered low-field sites within a mullite ceramic host. The results indicate that the existence of these low-field ions, which are likely at sites in regions of disorder, accounts for most of the spectroscopic anomalies previously noted in these materials. Furthermore, energy transfer from ordered high-field to disordered low-field ions is observed. The resulting complex spectra are deconvoluted by means of the recently developed technique of saturation-resolved fluorescence spectroscopy.

The process of quenching of fluorescence from the /sup 3/P/sub 0/ state of Pr/sup 3 +/ in La/sub 0.72/Pr/sub 0.25/Nd/sub 0.03/F/sub 3/ due to cross relaxation to Pr and Nd ions has been investigated. The fluorescence decay of the ensemble of Pr ions after pulsed excitation is measured as a function of temperature in the (2-70)-K region. Cross relaxation occurs either directly or through a donor-donor transfer within the inhomogeneous line. Knowledge of the dynamics occurring within the inhomogeneous line derived from previous fluorescence line-narrowing experiments is used to analyze the cross-relaxation process from a microscopic viewpoint according to models for fluorescence decay in the presence of traps. In general the decay is consistent with an electric dipole-dipole transfer mechanism. At 2 K the decay can be well described by a direct transfer to Pr and Nd traps without donor-donor transfer. The temperature dependence of the decay at long times can be described for 35 < T < 70 K by the hopping model. The agreement with theory is much better if the cross relaxation to Nd ions is assumed to occur mainly via the lowest Stark level of the /sup 4/I/sub 9/2/ manifold.

We report fluorescence line narrowing (FLN) studies of the magnon sideband of $^{4}T_{1}\ensuremath{\rightarrow}^{6}A_{1}$ transitions in Mn${\mathrm{F}}_{2}$:${\mathrm{Zn}}^{2+}$. We have successfully isolated magnon sideband profiles of near-resonant subsets of ${\mathrm{Mn}}^{2+}$ ions from within the inhomogeneously broadened line at ${\mathrm{Zn}}^{2+}$ concentrations up to 3%. Since the sideband profile mirrors the magnon density of states, this demonstrates the feasibility of using FLN to study local low-energy collective modes, such as spin waves, in highly disordered materials.