A. Suchocki

Photoluminescence studies of Mn4+ ions in YAlO3 crystals at ambient and high pressure

Detailed investigations of the photoluminescence properties of Mn4+ (3d3) ions in YAlO3 have been performed in the temperature range 10–600 K. The luminescence of Mn4+ ions due to the transition consists of two zero-phonon lines (R lines) at 691.3 and 692.7 nm, which became visible only at low temperature, and their vibronic sidebands that cover the range of 660–740 nm. The thermal quenching of the luminescence intensity due to the non-radiative decay occurs at temperatures above 420 K. The temperature dependence of the luminescence decay time shows a quasi-linear decrease from τ = 4.9 to 1.6 ms in the temperature range from 90 to 420 K (with a temperature coefficient −0.01 ms K−1) that makes YAlO3:Mn a potentially good phosphor for a fibre optic fluorescence thermometer in this temperature range. The high-pressure low-temperature luminescence measurements in a diamond-anvil cell reveal similar pressure coefficients for Mn4+ and Cr3+ dopant ions in YAlO3, equal to 1.16 cm−1 kbar−1 and 1.08 cm−1 kbar−1, respectively.

CdF2:In: A novel material for optically written storage of information

We demonstrate that semiconducting CdF2 crystals doped with indium is an efficient medium for optical storage of information in static and dynamic regimes. A metastable phototransformation of 1018 cm−3 In centers from a localized deep state to a hydrogenlike shallow state leads to a change of the refractive index Δn of about 10−4 for the probe beam at the wavelength of 500 nm. The diffraction efficiency is temperature dependent due to spontaneous decay of the grating caused by thermal recovery of the In impurity from the metastable hydrogenic state to the localized ground state.

Crystal structure of GdFeO3-type rare earth gallates and aluminates

Abstract The crystal structures of the lanthanum and neodymium gallates and yttrium aluminates, doped with neodymium and erbium were investigated by means of X-ray structure analysis (full profile Rietveld refinement, powder diffractometers HZG-4 and DRON-4, Cu and Co Kα-radiation). A comparative crystallochemical analysis of the studied structures was performed. All examined compounds belong to the orthorhombically distorted GdFeO3-type of structure, space group Pbnm, Z=4. It is shown that the structure deformation parameters such as the rare earth cation shift, the bond length distortion of the polyhedra, and the tilt angles of octahedra increase in the sequence: LaGaO3–NdGaO3–YAlO3:Nd–Y0.5Er0.5AlO3.

Influence of high pressure on the luminescence transitions of Mn4+-doped gadolinium gallium garnet

We present results of a high-pressure photoluminescence study of Mn- and Ca-doped gadolinium gallium garnet (GGG) crystals. Since the Mn4+ ion has the same electronic structure of the open 3d3 shell as Cr3+, its spectroscopic properties are expected to be similar to those of the Cr-doped GGG. We observed the luminescence R-lines of various Mn4+ centres in GGG. In the 0–118 kbar pressure range those R-lines shift linearly to lower energies. The pressure coefficients are of the order of 2 cm−1 kbar−1, about three times larger than that for Cr3+ ions. This fact can be explained by different strength of coupling of isoelectronic Cr3+ and Mn4+ ions with GGG host. The changes of the radiative decay times of the Mn4+ centres as a function of pressure are fitted with a theoretical model.

Laser‐induced grating spectroscopy of cadmium telluride

Laser‐induced transient gratings produced by two‐photon absorption of picosecond pulses at 1.064 μm were used to examine the room‐temperature nonlinear optical responses of CdTe crystals with different types of conductivity. Pulse‐probe degenerate four‐wave mixing measurements of grating dynamics on subnanosecond time scales were used to measure the ambipolar diffusion coefficient (Da) of charge carriers in the crystals. The value of Da =3.0 cm2 s−1 which was obtained is in very good agreement with theoretical estimates. A long‐lived contribution to the signal consistent with a trapped charge photorefractive effect was observed at large grating spacings for n‐type conductivity, and is tentatively attributed to a larger trap density in this sample. Measurements of the relative scattering efficiencies of successive diffracted orders in the Raman–Nath regime allowed for calculation of the laser‐induced change in the index of refraction, due to the creation of free carriers. The value of Δn=4×10−4 which was o...

Growth and Induced Color Centers in YAlO3-Nd Single Crystals

Color centers created during growth processes as well as formed under various external influences (UV and γ-irradiation, thermal treatments) are studied in YAP–Nd crystals obtained under different technological conditions. The role of impurity ions (including Fe and Cr) in growth and induced crystal coloration as well as models of color centers are discussed.

Influence of color centers on optical and lasing properties of the gadolinium gallium garnet single crystals doped with Nd3+ ions

The mechanisms of creation of the stable color centers generated in GGG-Nd crystals under the influence of UV light and various kind of ionizing radiation (gamma-rays and electrons) are examined. The models of stable color centers in these crystals are proposed. Influence of gamma-irradiation on the GGG-Nd crystal laser generation characteristics is studied. Absorption spectra and decay kinetics of the transient color centers, induced in GGG-Nd by pulsed UV light, are investigated.

Electronic structure of Ce3+ multicenters in yttrium aluminum garnets

Low temperature, infrared, and visible-ultraviolet absorption spectra of yttrium aluminum garnet (YAG) bulk crystals and epitaxial layers doped with Ce are presented. In the region of intra-configurational 4f–4f transitions, the spectra of the bulk YAG crystals exhibit existence of at least two different Ce3+ related centers, a major one associated with Ce in regular positions substituting yttrium and also additional center, due to so called antisite positions in the garnet host, i.e., ions in the Al positions. Crystal field analysis based on exchange charge model exhibit excellent agreement with the experimental data for major Ce3+ center.

Crystal structure of LaGaO3 and (La,Gd)GaO3 solid solutions

Abstract The LaGaO 3 crystal structure was investigated by means of X-ray structure analysis (powder diffractometer HZG-4, CuK α ): structure type GdFeO 3 , space group Pbnm, a =5.52299(8) A; b =5.49138(9) A; c =7.7725(1), A, Z =4, R I =0.098. The shortest interatomic distances (A) are: Ga–O, 1.967(3); La–O, 2.46(3) ; O–O, 2.77(4); Ga–Ga, 3.8862(1); La–Ga, 3.287(1); La–La, 3.866(5). Atoms have the following coordination numbers: La, 9 or 10; Ga, 6. Compounds formed in the LaGaO 3 –GdGaO 3 quasibinary system have been studied. An anomalous behaviour of the La 1− x Gd x GaO 3 solid solution lattice parameters has been observed.

Spectroscopic properties of alexandrite crystals II

Abstract Several aspects of the optical spectroscopic properties of alexandrite crystals not previously investigated are reported here. For Cr3+ ions occupying the Al3+ lattice sites with mirror symmetry in BeAl2O4, the positions of the zero-phonon lines for absorption transitions to the 2T1g and 4T2g levels are identified, and vibronic transition peaks in the fluorescence spectrum are compared to transitions appearing in the Raman spectrum and Stokes excitation spectrum. In addition, the effects of radiation trapping are shown to lengthen the fluorescence lifetime of the 2Eg - 4A2g transition for ions in these sites at low temperatures. For Cr3+ ions occupying the Al3+ lattice with inversion symmetry, the ground state splitting of the 2Eg - 4A2g transition is reported and the decrease of the fluorescence lifetime with temperature is shown to be due to the increase in vibronic emission probability as well as increased probability of direct radiationless decay.