Rm Montereali

Spontaneous emission properties of color centers based optical microcavities

Abstract Optical microcavities based on lithium fluoride films treated by low-energy electrons to create visible-emitting F2 color centers have been fabricated, and their radiative properties characterized for the first time. By tuning the photon cavity mode to the maximum of the luminescence band for the F2 centers (∼670 nm), spectral narrowing, peak-intensity enhancement of the emission band as well as a highly directional radiation pattern have been observed comparatively for experiments performed on a half-cavity and a full microcavity. Spontaneous emission decay times have been measured, and a shortening of lifetime by the cavity has been observed.

Control of F2 color centers spontaneous emission in LiF thin films inside optical microcavities

Abstract An experimental investigation on spontaneous emission properties of Fabry–Perot microcavities consisting of quarter-wavelength ZnS/Cryolite Bragg mirrors and a lithium fluoride (LiF) thin film colored with low-energy electron beam lithography is reported for the first time. Angular-resolved photoluminescence measurements show the modifications of F2 color centers visible spontaneous emission. The resonator induces a narrowing of the emission spectrum and a related increase in the directionality and intensity of the emission along the cavity axis.

Emission dynamics of heavily coloredLiF crystals

SummaryLiF crystals colored with ionizing radiation have been used in recent times as active materials for pulsed laser emissions in the visible and near infrared region of the electro-magnetic spectrum. Among the various color centers which possess high emission efficiencies, the F3+ center displays a peculiar optical cycle whose properties depend on temperature and pumping intensity. However a few effects discovered recently seem to imply the existence of interactions among the centers, which is a topic of paramount importance for applied and basic research. Preliminary results on samples containing high concentration of color centers have shown new dynamical effects, which in part can be explained in the frame of nonlinear optical processes and in part require a different approach in describing the optical cycle and its parameters.

Emission and excitation spectra of silicon-related luminescent centers in CVD-grown diamond films

Abstract Luminescence properties of silicon-related centers in CVD-grown diamond films and their spatial distribution along the growth direction have been investigated. It is found that the lineshape and peak position of the emission band depend both on excitation energy and light focalization depth, suggesting the coexistence of two optical centers related to isolated vacancies and to silicon-vacancy complexes. A simple model of the electronic structure of this defect is proposed.

Influence of nitrogen and temperature on the plasma deposition of fluorinated amorphous carbon films

In this work, the effects of nitrogen addition on the properties of a-C:H:F films produced by rf plasma enhanced chemical vapor deposition at different temperatures are reported. The structural and optical properties were investigated by x-ray photoelectron spectroscopy, Raman spectroscopy, ultraviolet-visible transmittance and ellipsometry measurements. The dependence of both fluorine and nitrogen incorporation in the carbon matrix on the deposition temperature was analyzed. The main effect of progressive nitrogen incorporation is a decrease of transmittance and optical band gap of the samples grown at room temperature and at 400u200a°C. Raman spectra evidence that for films deposited at 400u200a°C a sudden loss of sp3 carbon bonding occurs. In particular, at fixed plasma composition, the decrease of the optical band gap is interpreted as a clustering of the existing sp2 carbon sites. Ellipsometry characterization indicates that nitrogen incorporation for the samples deposited at room temperature induces an incr...

Color center luminescence decay times in optical microcavities based on LiF films

Abstract Controlling and modifying spontaneous emission in optical microcavities is of great interest for both their basic properties and for their potential applications in emitting solid-state devices. Spatial and temporal spontaneous emission modifications of F 2 color centers in LiF films placed inside planar optical microcavities are reported. Angularly resolved photoluminescence measurements show a narrowing and an enhancement of the emission spectrum along the cavity axis; time resolved luminescence measurements in different geometrical configurations show a shortening of luminescence decay time along the microcavity axis.

Structural and optical properties of alkali halide multilayer LiF:NaF films

Alkali halide multilayer films containing a large concentration of color centers created by low energy (3–12 keV) electron beams in a thin dielectric layer of controlled depth, represent a good and simple way to obtain new optically active materials. This work presents a study of multilayer LiF:NaF films, grown by physical evaporation. The structural and morphological characterization of the samples have been performed using x-ray diffraction, scanning electron microscopy, atomic force microscopy, and x-ray photoemission spectroscopy depth profile techniques. The visible photoluminescence of optically active defects was measured by excitation with an Argon laser. Controlling the deposition and coloration parameters it is possible to obtain new photoluminescent materials with predesigned optical features.

Structural and optical properties of low nnergy electrons irradiated KCl:LiF multilayer films

Abstract The optical behaviour of point defects created by low energy electron beams is studied in multilayer KCl:LiF films, grown by thermal evaporation onto amorphous substrates at constant temperatures ranging from 30 to 350°C. The surface morphology of the samples was observed by the atomic force microscopy (AFM) technique. Large concentration of F and F-aggregate centres has been produced by 3–7 keV electron irradiation both in KCl and LiF layers which constitute the film. By pumping our films with appropriate Ar + laser lines, we measured, for the first time, the luminescence in the near infrared region due to F 2 and F 3 centres in KCl and the typical emission of F 2 and F 3 + centres in LiF in the visible region.

Broad band emitting color centers in lithium fluoride films for optical microcavities

Abstract We have fabricated for the first time different optical microcavities made of two Bragg mirrors sandwiching a lithium fluoride film treated by low-energy electrons to create color centers. Among the so-formed defects, we focused our attention on the F2 centers, which can be optically excited around 450 nm and give rise to an efficient broad-band luminescence centered at ∼ 670 nm in the red spectral range at RT. We have modified the design of the upper reflector of the microcavities in order to shift their resonant wavelength from λres ≈ 665 nm to λres ≈ 640 nm. We get evidence of the different optical behaviors from measurements of the photoluminescence spectra of the radiation emitted perpendicularly to the multilayer surface.

LUMINESCENCE OF AGGREGATE COLOR CENTERS IN KF

Abstract Complex F-aggregate centers were studied in pure and Li 1 -doped KF, by means of optical excitation. Three new emission bands in the near infrared region were revealed. Among them, the luminescence at 1040 nm was identified as the emission of F 3 defects because of its excitation, its peak position and its enhancement under irradiation at room temperature with F light. The luminescences at 950 and at 1250 nm were too weak and could not be unambiguously identified. However, they are probably due to complex F-aggregate centers, like F 4 defects.