V. S. Khomenko

Blue Photoluminescence of Oxidized Films of Porous Silicon

It is found that the films of n+-type porous silicon of low (10–50%) porosity exhibit photoluminescence in the region 400–500 nm after a 5-month storage in an air atmosphere. The spectrum of blue photoluminescence of the least porous but strongly oxidized films has maxima at 417, 435, and 465 nm. The same spectrum structure manifests itself upon the introduction of an Er3+- and Yb3+-containing complex. The mechanisms of blue photoluminesence are discussed.

Luminescence of an erbium- and ytterbium-containing complex in porous silicon films

Er3+ and Yb3+ ions are introduced into porous silicon films, stabilized by oxidation in an oxygen plasma, in the form of a gadolinium oxychloride-based luminophor by means of thermal diffusion. An investigation is made of the luminescence and photoexcitation spectra of samples with Er3+ (10 and 30 wt.%), Yb3+ (10 wt.%), and Er3, Yb3++ (10 wt.% each). It is shown that the intense IR luminescence (1.00 and 1.54 μm) is caused by cross-relaxation effects. The most effective excitation of the luminescence has been observed in the UV absorption band of the porous silicon.

Cross-relaxation effects in the luminescence of erbium at 1.5 ?m

This paper reports on the experimental and theoretical investigation of the influence of the processes of intercenter relaxation on the /sup 4/I/sub 13/2/ ..-->../sup 4/I/sub 15/2/ luminescence of erbium in polycrystalline yttrium oxychloride under resonance excitation. The kinetics of the emission of samples with different concentrations of Er3/sup +/ ions were measured. Numerical calculations of the dependence of the lifetime of the /sup 4/I/sub 13/2/ state on the erbium concentration for different values of the stationary excitation power were carried out. The experimental dependence of the luminescence decay time on the concentration of the impurity ions constructed on the basis of data from kinetic measurements is interpreted on the basis of an examination of the cross-relaxation processes under the conditions of pairwise interactions. It is determined that the power of the exciting radiation along with the concentration of the impurity ions is the main factor determining the role of intercenter relaxation in the luminescence of erbium along the /sup 4/I/sub 13/2/ ..-->../sup 4/I/sub 15/2/ channel due to the nonlinear nature of the dependence of the rate of the cross-relaxation processes which sum the electronic excitation acts on the flux density of the IR radiation.

Concentration Effects Manifesting Themselves in the Luminescence of Tm3+ Ions in an Oxychloride Matrix

We investigated the luminescence characteristics of Tm3+ ions depending on their concentration in an oxychloride matrix. We measured luminescence spectra, luminescence excitation spectra, concentration dependences of the intensity and kinetics of various luminescence bands of rare‐earth ions of the visible and IR ranges at different excitation wavelengths. We carried out calculations of the concentration dependences of the quantum yield of luminescence: total and individual spectral bands. The cross‐relaxational nature of concentration effects in the luminescence of rare‐earth ions is discussed.

Luminescence of Tm3+ Ions in Yttrium Oxide

The concentration and temperature dependences of the blue luminescence intensity of the Tm3+ ion in yttrium oxide under UV and IR excitation have been measured. We made a proposal that the main role in the formation of these dependences is played by the interionic cross relaxation of excited states of Tm3+; the presence of admixed secondary rare‐earth ions can strongly influence the shape of the temperature dependence of the anti‐Stokes luminescence intensity, displacing the position of its maximum. It is shown that the quenching action of admixtures under Stokes and anti‐Stokes excitation shows up differently because of the differences in the mechanisms of population of the luminescent level.

Luminescence of porous silicon films with an europium-containing complex

We obtained porous silicon films modified at room temperature by an Eu3+-containing polymer complex. The most intense photoluminescence of Eu3+ implanted in the porous silicon was observed at the wavelengths of 611, 618, 691, and 704 nm. In this case, the intensity of the intrinsic photoluminescence of strongly irradiated specimens of porous silicon decreased, while the intensity of weakly emitting films multiply increased. An investigation of the photoexcitation spectra made it possible to establish the effect of Eu3+-containing complexes on the mechanism underlying the excitation of photoluminescence of porous silicon.

Temperature dependence of the antistokes luminescence of holmium in yttrium fluoride

This paper analyzes the effect of temperature on the intensity of the green and red luminescence bands of Ho/sup 3 +/ ions in yttrium fluoride excited in the absorption band of ytterbium. The relative intensity of the two luminescence components was measured in the temperature range of 77-400/sup 0/K by integrating the emission spectra in the 0.54- and 0.65-..mu..m regions. The population of the /sup 5/S/sub 2/ and /sup 5/F/sub 3/ levels of Ho/sup 3 +/ were calculated on a computer from the temperature-dependent variation of the rates of many-phonon nonradiative relaxation and electronic excitation energy transfer.

X ray phase and spectro-luminescence analyses of oxychlorides of rare-earth elements

This study conducts x-ray phase and spectroluminescence analyses and studies the thermal dependence of the intensity of anti-stokes luminescence for a series of oxychlorides of yttrium and gadolinium. For samples which differ in their ytterbium composition, the authors present the spectra for x-ray diffraction and the spectra of luminescence in the range of 0.55 and 0.67 micro for excitation at lambda - 1 micro. Measurements of x-ray diagrams for the gadolinium oxychloride samples are similar for a change in the concentration of ytterbium from 0 to 20 mol.%. The x-ray data for the yttrium oxychloride samples are presented.

Effect of ytterbium on erbium anti-stokes luminescence in the 1.5-?m radiation range

This paper describes the effect of ytterbium on the luminescence of yttrium oxychloride with erbium ions at different temperatures. The intensity of the anti-Stokes luminescence was estimated from the integrated emission spectra of erbium. The spectra were recorded with a luminescence apparatus consisting of a grating monochromator with a reciprocal dispersion of 8 A.mm/sup -1/ and an electrometric voltmeter. The authors conclude that over the whole temperature range, Yb/sup 3 +/ enhances the red anti-Stokes luminescence of erbium and has a weak quenching effect on the green component. Both enhancement and quenching effects can be described by a model based on cross-relation interactions between pairs of Er/sup 3 +/ ions, energy transfer between ytterbium and erbium, and the temperature dependence of the rate constants for all these processes. The authors also observed a strong attenuation of the green emission in the presence of ytterbium, which is caused by additional quenching due to impurities.