Er3+-doped silica glass (up to 10 wt%) was synthesized by sol-gel processing with the addition of 3- aminopropyl trimethoxysilane (APS) as a complexing agent. Er3+ ions reacted with amino groups and, thus, linked to the silica network during the sol preparation. As a result, the motion of Er3+ ions was restricted and the formation of Er3+ clusters was inhibited. Both fluorescence spectra and magic-angle spinning (MAS) nuclear magnetic resonance (NMR) indicated that the addition of the complexing agent APS resulted in a homogeneous dispersion of high-level Er+3 doping in the resultant gels. After the removal of organic components, however, Er+3 clustering occurs when firing at a high temperature for a long period of time, e.g. at 1000°C for 10 hrs, due to enhanced Er3+ diffusion.

Ge-Ga-S-glasses doped with 15000 mole-ppm Pr3+ have been developed for applications in optical amplifiers for 1.3 μm. The formation of crystalline phase separations in Ge 25 Ga10 S65could be suppressed by modification of the glass composition with Sb. Samples have been prepared by melting in sealed silica ampoules at 950°C. Ge-Ga-Sb-S-glasses, doped with 15000 mole ppm Pr3+, were synthesized by addition of Sb2S3up to contents of 14.3 mole% to the composition Ge25,Ga10S65. (corresponding to 83,3GeS2-16,7Ga2S3) or by replacing up to 50 mole% of Ga by Sb. Transparent to opaque glasses were obtained which were free from crystalline phase separations. The modification of the glasses with Sb leads to a remarkable decrease of the transformation temperature of the glasses. However, the temperature working range remains almost unaffected. The transparent glasses exhibit with 15 – 18 μs the same fluorescence lifetimes and the same fluorescence maximum position (1340– 1341 nm) and FWHM (63 μm) as the unmodified Ge-Ga-S-glass. The preparation process for both glass systems could be optimized to obtain monoliths with lengths of several centimeters and intrin- sic optical losses of only 0.05 dB/cm at 1.3 μm (after correction of reflection), which is of very high importance for the future development of planar amplifiers with remarkable net gain.

A method for obtaining time and frequency resolved spectra with high spectral and temporal resolution over a broad spectral range is presented. Step – scan Fourier transform spectroscopy permits spectral coverage from UV to mid IR with sub nanosecond resolution making it possible to track emission from multiple manifolds with full temporal resolution in a single experiment. Data for several rare-earth doped crystalline materials exhibiting multiple emission bands and including evidence of energy transfer is shown.

We have recently observed spectrally resolved vibronic structure and luminescence intermittency from nanometer-size porous silicon nanocrystals. In this study we examine the quantum efficiency of a single nanoparticle and show that emitting nanoparticles do so with near unity quantum efficiency. This result suggests that the emission from porous Si nanoparticles, and thus bulk porous Si, results from a small number of high quantum efficiency emitters. In our previous work we have shown that our nanoparticles contain more than one coupled chromophore. In order to examine these effects more closely we employ several spectroscopy and microscopy techniques including: 1) single-particle spectroscopy, 2) shear-force microscopy, and 3) time-resolved spectroscopy, on a colloidal suspension of size-selected, surface-oxidized nanoparticles. In addition we apply statistical techniques to provide a more complete picture of the coupling between chromophores in a given nanoparticle.

We studied the effect of post-anodization chemical etching on porous silicon by means of photoluminescence (PL), Fourier transform infrared (FTIR) absorption and Raman spectroscopy. We performed these measurements with repeating etching and then observed the variation of the spectra. On the basis of the correlation between PL and FTIR spectral changes, the PL emission at 660 and 730 nm in PL spectra stems from Si-H2, and Si-H clusters at surface, respectively. Raman spectra show a close relation between PL emission at 850 nm and nanocrystallites in porous silicon. In addition, chemical etching contributes to the promotion of nanocrystallites and to dissolving them.

We are investigating applicability of photoacoustic (PA) spectroscopy to porous silicon. Since PA spectroscopy is based on a non-radiative relaxation process, the measurement is of importance as a counterpart to photoluminescent spectroscopy. We studied a dependence of a PA amplitude on a chopping frequency and discussed the influence of a PA signal originated in a silicon substrate. The frequency dependence was elucidated with a two-layer model. Differences in PA spectra are correlated with a photoluminescent efficiency. From the correlation, we believe that non-radiative centers quench the efficiency.

In the present paper we report on time-resolved resonant and non-resonant fluorescence line narrowing measurements on a lead germanate glass doped with Eu3+. Site-selective decay curves were measured at low temperature. The results show that energy transfer processes between Eu3+, ions in different sites are not efficient at the doping level under investigation (I mol% Eu2O3). The homogeneous linewidth of the 5D0→47F0transition was measured at room temperature as a function of the excitation energy within the inhomogeneous profile. The linear dependence of the homogeneous linewidth on the excitation energy is discussed.

A polyaniline contact layer was deposited via microemulsion polymerisation which resulted in nanosize short-chain polymer particles that penetrate deeper into the pores of porous silicon than polymers deposited by other more conventional methods. The microemulsion method gives a contact with higher chemical electroluminescence efficiency due to a larger area of actively emitting porous silicon.

In this article, we discuss the nature of the high lying states in rare earth activated systems and their effect on the luminescence efficiency of these systems. We show that by comparing the optical spectra of these materials with complementary measurements such as photoconductivity (PC), the absolute energy level structure of the ions with respect ot the intrinsic bands of the host can be determined. We propose new measurements which will provide insight on the manner in which energy delocalizes in activated solids.

The photoluminescence response of a series of porous silicon samples, obtained by electrochemical etching of n-type CZ-silicon, has been recorded in various gas environments. A quenching is reported when porous silicon is in the presence of an oxidising ambient (dry air or acetone vapours in dry air). Process reversibility depends on the duration of laser illumination. Quenching is also recorded if porous silicon is in the presence of acetone vapours in nitrogen ambient, where complete reversibility is however shown. Moreover, the peak wavelength is red shifted in dry air and blue shifted in acetone vapours. Irreversible quenching is related to the growth of a thin oxide layer on the emitting nanostrucures.

Chromium-doped yttrium orthosilicate Cr:Y2SiO5 was studied by electron paramagnetic resonance (EPR) method at 9.5–9.7 GHz. EPR transitions were observed for Cr4+ substituting Si4+ in tetrahedral sites of Y2SiO5, and orientation dependence of the single crystal EPR spectrum was studied. The ground state of Cr4+ (electron configuration 3d2) in Y2SiO5 is a spin triplet (S = 1). Rhombic symmetry of the electron magnetic dipole-dipole interaction (zero field splitting) leads to three electron spin terms Tx, Ty and Tz in the absence of the external magnetic field. We have observed the magnetically induced anti-crossing of the terms Ty and Tz.We show that in the vicinity of energy level anti-crossing the linewidths and positions of the resonance lines depend on temperature.

Plasma-enhanced CVD (PECVD) deposited alumina (A12O3) thin films and single sapphire crystals were co-doped with both erbium and ytterbium using ion implantation. Yb3+ and Er3+ concentrations ranged from 2.4At% to 8At% and from 0.4At% to 0.8At%, respectively. The samples show relatively strong, broad, room-temperature photoluminescence (PL) at λ=11.53µm corresponding to the intra-4f transitions between the 4I13/2 (first excited) and the 4I15/2 (ground) state of Er3+. The full width at half maximum (FWHM) of the emission spectrum is as high as 67nm for the A12O3 thin films; for the sapphire crystals it is 45nm. The fluorescence lifetime of the samples has been measured to be as high as 4.2ms at 50mW laser pump power. The indirect pumping of erbium through the transfer of energy from ytterbium has been demonstrated and the PL peak intensity has been studied as a function of the Yb3+/Er3+ concentration ratio when the samples are pumped at 514nm and 850nm; the PL excitation spectrum (PL at 1.53gm as a function of pump wavelength) of an Er3+/Yb3+ co-implanted sample is also presented. Both the PL peak intensity at 1.53µm and the fluorescence lifetime have been studied as functions of annealing temperature. Luminescence spectra attributed to defects in the alumina matrix are presented for as-implanted samples and following thermal annealing.

Ce3+ luminescence in yttrium cerium aluminium borates was studied. A substantial red shift in photoluminescence and low-voltage cathodoluminescence spectra was found to be induced by Ce concentration increase. Complicated concentration dependence of emission intensity and strong influence of cerium content on emission wavelength suggest strong activator-host interaction in rare earth borates.

For white light generation with LUCOLEDs the phosphors on the base of YAG:Ce are ideally suited. The variation of the phosphor composition were performed. Powder Ga-substituted phosphors as well as Lu,Y,La,Sc- substituted epitaxial films were investigated. The effects on luminescence and excitation spectra, which is relevant for luminescence conversion, are reported.

A number of groups have demonstrated an efficient excitation transfer mechanism in erbium-doped crystalline and porous silicon. It has been postulated that this is a carrier-mediated transfer, which points to the possibility of fabricating efficient silicon-based 1.5 µm emitters.

We have previously reported the existence of a similar transfer mechanism in silicon-rich silica. In this paper we extend this study to include silicon nanopowders and demonstrate the existence of the same mechanism. Comparing the photoluminescence excitation spectra of erbium doped silica, silicon-rich silica and silicon nanopowders we show that the coupling mechanism enables broad-band pumping of the rare-earth ion.

We have also measured carrier lifetimes in the nanoclustered silicon materials using photoinduced free carrier decay. The measured lifetimes are surprisingly long (in the 2-10 millisecond regime), and we discuss the effect of this on the transfer mechanism.

As the ultra-violet/blue luminescent material, we will introduce the thermal treated cerium oxide on silicon. It has been confirmed a violet/blue luminescence ranging from 358 rim to 450 rnm at room temperature from the thermally treated cerium-dioxide thin films on silicon. As a results of AES and HR-TEM measurement, it was confirmed that cerium silicates were generated by thermal treatment. These cerium silicates such as Ce4.667(SiO4)3O and Ce2Si2O7 are the source of the ultra-violet (UV) emission ranging from 358 nim to 450 nm (maximum at 388 rim).

The results of a photoluminescence (PL) study of synthetic diamonds annealed over the temperature range 1500-2500°C are presented. For nickel- and nitrogen-containing diamonds a number of new, previously undocumented PL systems with zero-phonon lines (ZPLs) at 598.5, 622.6, 638.9, 752.1 and 877.2 nm has been found. Photoluminescence excitation (PLE) spectra for PL systems with ZPLs at 727.1 and 746.6 nm have been measured for the first time. Preliminary results on annealing behavior of the PL centers have been obtained. Of all the PL systems observed only that ones with ZPLs at 752.1 and 793.0 nm together with the S2 and S3 optical centers are present in diamonds annealed at temperatures higher than 2200°C.

The electric field dependence of emission of carriers from deep impurities in semiconductors has been investigated applying static and terahertz electric fields. It is shown that at high electric field strengths carrier emission is dominated by phonon assisted tunneling which may easily be recognized by plotting the emission rate as a function of the square of the electric field strength in a log-lin plot giving a straight line. For charged impurities the transition from phonon assisted tunneling to Poole-Frenkel effect at low fields can be traced back.

Cathodoluminescence and its temperature-dose behaviour of different modifications of SiO2 are presented. The detected luminescence bands are attributed to three optical active luminescence centers: the twofold coordinated silicon center (=Si:), the non-bridging oxygen hole center (NBOHC) and the self-trapped exciton (STE). The experiments are correlated with infrared absorption measurements. Existing structural models are discussed with reference to our results.

We have studied the effect of level mixing on the optical properties of Er in Si by calculating the radiative cross sections of Er in Si under external pressure, and the possibility of enhancing in this way both the luminescence and the excitation efficiency.