S. Golab

Spectroscopy of crystals

The polarized absorption spectra, time-resolved emission spectra, and emission lifetimes of doped crystals were measured. An intense emission from the level was observed. The positions of the levels, experimental oscillator strengths, and branching ratios from the and levels were determined. The results are discussed in terms of the Judd - Ofelt parameters.

Conversion of infrared radiation into red emission in YVO4:Yb,Ho

Upon continuous wave excitation around 1 μm, a YVO4 crystal codoped with ytterbium and holmium exhibits intense red emission originating in the 5F5 level and considerably weaker green emission originating in the 5S2 level of Ho3+. The ratio of the red to green emission intensities is 17:1 at 300 K. The dependence of the intensity of both emissions on the pump power is nearly the same but the mechanisms determined on the basis of short pulse excitation are found to be different. It is concluded that the green emission is excited by two consecutive energy transfers from Yb3+ to Ho3+, whereas excited state absorption is involved in the excitation of red emission.

Optical spectra of a LaGaO3 crystal singly doped with chromium, vanadium and cobalt

Abstract Crystals of lanthanum orthogallate containing chromium, vanadium or cobalt were grown by the Czochralski method and their optical spectra were measured at room and 5K temperature. Recorded absorption and luminescence spectra of chromium ions which are convenient probes of number and type of available sites revealed that Cr3+ ions in LaGaO3 occupy identical sites with distorted octahedral symmetry and consistent with a strong crystal field case. Absorption spectra of vanadium doped LaGaO3 have been attributed to V4+ and V3+ ions coexistent in the matrix whereas a short lived and broad band luminescence recorded in the 12000–15000 cm−1 region has been attributed to the 2E–2T2 transition of V4+ ions. Absorption spectra of LaGaO3 doped with cobalt were found to be consistent with a mixed valency system containing Co2+ and Co3+. This activator–host combination did not show luminescence strong enough to be recorded with our detection systems.

Effect of temperature on excitation energy transfer and upconversion phenomena in Er:YVO4 single crystals

Abstract Investigation of excitation and decay of Er 3+ in YVO 4 single crystals has been carried out at temperature range from 5 to 500 K. In the limit of low Er 3+ content, the temperature dependence of the 4 S 3/2 decay is not consistent with predictions of multiphonon relaxation model. In heavily doped crystals the 4 S 3/2 decay is governed by cross relaxation process, whose rate grows steadily with increasing temperature. An efficient upconverted luminescence near 550 nm following a cw and short pulse (5 ns) excitation of the 4 I 9/2 level in the system under study has been recorded and analysed. Contribution of the excited state absorption to these phenomena has been considered.

Influence of temperature on luminescence of terbium ions in LiNbO3

Single crystals of LiNbO3 doped with terbium were grown by the Czochralski method and their optical properties were examined. It has been found that, in contrast to isostructural LiTaO3:Tb, the terbium ions in LiNbO3 exhibit intense luminescence at low temperatures only, up to about 150 K. At this temperature, a luminescence quenching mechanism with activation energy of 0.22 eV is switched on. As a consequence, the luminescence of LiNbO3:Tb is reduced to a negligible level at room temperature.

Passive mode locking of a Nd3+:SrLaGa3O7 laser

A Nd3+:SrLaGa3O7 laser with a pentacarbocyanine dye cell produced regular 25–30 ps pulses over the period of the flash lamp. Output energy as a function of mirror reflectivity and lamp energy was also determined.

Thulium-doped Ca4GdO(BO3)3 crystals. An investigation of radiative and non-radiative processes

An extensive investigation of optical properties was carried out for Tm3+-doped Ca4GdO(BO3)3 crystals in the 5-300 K temperature range. Based on absorption and emission spectra at 5 K, crystal field levels of active ions have been located. Non-equivalent sites for Tm3+ in the Ca4GdO(BO3)3 matrix have been demonstrated. Lifetimes and the fluorescence dynamics were studied as a function of temperature and concentration of thulium ions. The Judd-Ofelt analysis of absorption spectra and the Inokuti-Hirayama model for energy transfer between activator ions provided information on radiative processes and non-radiative relaxation of excited states. Additionally, multiphonon emission was taken into account to explain a very strong quenching of the 3H4 and the 3F4 fluorescence.

K5LaLi2F10:Er3+ crystals. Growth, structure and optical properties

Single crystals of K5LaLi2F10:Er3+ and K5LaLi2F10 were synthesized and the structural determination was made by x-ray diffraction analysis. The structure is orthorhombic with space group Pnma. The unit cell parameters are: a = 20.775, b = 7.822 and c = 6.963 A. The infrared transmission and Raman scattering spectra of oriented single crystals were measured and discussed in terms of factor group analysis and x-ray structure. A vibrational assignment is proposed. Preliminary optical properties of Er3+ ions in K5LaLi2F10 crystals have been investigated using absorption, luminescence and lifetime measurements in the 5-300 K temperature range. The low temperature absorption and luminescence spectra of Er3+ have allowed us to identify the Stark levels of low-lying multiplets. The luminescence observed at 5 K has been attributed to the 4S3/24I15/2 (18 300 cm-1), 4F9/24I15/2 (15 000 cm-1), 4S3/24I13/2 (11800 cm-1) and 4I11/24I15/2 (10000 cm-1) transitions. The lifetimes of selected excited states were measured at 5 and 300 K temperature. The obtained data gave the first insight into the luminescent properties of Er3+ ions in the fluorine surroundings in K5LaLi2F10 crystals.

Spectroscopic properties of holmium doped crystals

The spectroscopic properties of ions in crystals have been investigated using optical absorption, luminescence and lifetime measurements in the 5-300 K temperature range. The low temperature, polarized absorption spectra of in this matrix have allowed us to identify the Stark levels of the different multiplets up to 30 000 . The results are consistent with symmetry for the rare-earth ions and a singlet A character for the lowest Stark level of the ground state. Several transitions show additional structure which indicates multi-site occupancy for the ions. The measured oscillator strengths of the transitions between the J manifolds at 300 K are compared with those derived from the Judd-Ofelt theory. The radiative transition rates and radiative lifetimes have been calculated. The luminescence observed at 5 K has been attributed to (18 100 ), (15 060 ) and (13 150 ) transitions. The obtained data are used to discuss the radiative properties for luminescent levels of ions in the matrix. The emission cross-section of a potential laser line at 2 m connected with the transition is estimated.

Investigation of infrared-to-visible conversion in cubic Cs2NaErCl6 crystals

Efficient conversion of infrared radiation centred at 1 mu m into visible luminescence has been observed in cubic Cs2NaErCl6 crystals in which electric dipole transitions are forbidden by symmetry selection rules. Luminescence originating from the 4F9/2 and 4T9/1 levels of Er3+ increases strongly with increasing temperature in the 100-300 K region whereas the 4S3/2 luminescence appears to be independent of temperature. Experimental results are found to be consistent with non-resonant two-ion mechanisms involved in up-conversion and cross relaxation processes, the multiphonon decay being negligible.