Piotr Solarz

Dysprosium-doped YAl3(BO3)4 (YAB) crystals: an investigation of radiative and non-radiative processes

Abstract The absorption, emission spectra and lifetime of the 4F9/2 fluorescent level of Dy3+ in YAl3(BO3)4 crystal were investigated. Energy level structure was constructed from absorption and emission spectra recorded at 5 K. The measured oscillator strengths of the transitions between the J manifolds at 300 K were compared with those derived from the Judd–Ofelt theory. The radiative transition rates and radiative lifetimes were calculated. Although there are several transitions originating in the 4F9/2 level a major part of emission intensity is contained in the 4F9/2→6H13/2 transition. Measurement of selfquenching of the 4F9/2 luminescence provided a parameter characterizing an activator–activator interaction, which may be used to predict an optimal Dy3+ concentration. The narrow and polarization dependent emission lines, relatively long lifetime of the 4F9/2 metastable level (τ=520 μs) and its high quantum efficiency are advantageous for low threshold laser action in both CW and pulsed operation. The emission cross-section of a potential laser line at 570 nm connected with 4F9/2→6H13/2 transition was estimated.

Near-infrared ultrabroadband luminescence spectra properties of subvalent bismuth in CsI halide crystals

We observed two ultrabroadband near-infrared (NIR) luminescence bands around 1.2 and 1.5 μm in as-grown bismuth-doped CsI halide crystals, without additional aftertreatment. Dependence of the NIR emission properties on the excitation wavelength and measurement temperature was studied. Two kinds of NIR active centers of subvalent bismuth and color centers were demonstrated to coexist in Bi:CsI crystal. The eye-safe 1.5 μm emission band with an FWHM of 140 nm and lifetime of 213 μs at room temperature makes Bi:CsI crystal promising in the applications of the ultrafast laser and ultrabroadband amplifier.

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.

Near-infrared photoluminescence spectra in Bi-doped CsI crystal: evidence for Bi-valence conversions and Bi ion aggregation

Bi-doped CsI crystals exhibited near-infrared ultra-broadband photoluminescence around 1216 nm and 1560 nm, depending on the bismuth doping levels, which were ascribed to Bi+ and Bi2+ centers, respectively. The crystal chemistry of the Bi3+ to Bi+ reduction and Bi2+ dimer formation in CsI lattice were investigated. Thermal treatments including annealing and quenching were carried out to study the thermal behaviors of the two emission bands. The evolution of absorption and emission spectra of Bi:CsI crystals indicating the Bi-aggregation and valence conversions under thermal activation. The process of Bi aggregation was observed to be a second-order reaction with activation energy of 0.33 eV. Bi2+ was identified as the origin of the 1560 nm emission band with ESR spectra. A simple lattice structure diagram was developed to illustrate the physical processes in Bi:CsI crystals induced by thermal activation.

Crystal structure and optical study of Tm:Sc2SiO5 single crystal

Sc2SiO5:4 at. %Tm crystal was obtained by the Czochralski method and the crystal cell parameters were calculated. Sixfold coordinated Sc-ions occupied two different crystallographic sites but the low temperature optical spectra only represented energy transitions originating from Tm ions residing in one site. Room temperature absorption spectrum was analyzed in the framework of Judd–Ofelt theory and the calculated absorption coefficient and cross section were 10.47 cm−1 and 5.55×10−21 cm2 at 791 nm respectively. Stimulated emission cross sections for the F34–H36 transition near 1900 nm were evaluated using the reciprocity method while the luminescence F34 lifetime was measured to be 1.14 ms. We conclude that Tm:Sc2SiO5 is promising for diode-pumped infrared lasers.

Optical properties of YVO4 crystals singly doped with Er3+, Ho3+, Tm3+

In this work the spectroscopic properties of YVO 4 singly doped with erbium, holmium and thulium are considered. Multiphonon relaxation rates have been estimated. Stimulated emission cross sections for laser transitions in the near IR region have been assessed.

Optical study of erbium-doped La3Ga5.5Ta0.5O14 single crystal

Single crystals of erbium-doped La3Ga5.5 Ta0.5O14, grown by the Czochralski method, have been investigated using methods of optical spectroscopy. Room-temperature absorption spectra were analysed in the framework of the Judd-Ofelt theory. Radiative transition rates, radiative lifetimes and luminescence branching ratios for luminescent levels of Er3+ have been evaluated and compared to measured luminescence intensities and lifetimes. The laser potential associated with the 4I13/2-4I15/2 transition near 1.55 μm has been assessed. It has been concluded that La3Ga5.5 Ta0.5,O14:Er crystal is an intermediate gain laser material exhibiting strong inhomogeneous broadening of absorption bands, advantageous for optical pumping with laser diodes.

Anti-Stokes emission in undoped YVO4

Single crystal of nominally undoped YVO4 exhibits a broad-band emission centered at 450 nm when excited at any wavelength between 620–440 nm with short pulses delivered by an optical parametric oscillator. The broad-band emission has been assigned to the transition from the lowest energy excited states 3T1, 3T2 to the ground 1A1 state of the VO43−, whereas the excitation mechanism is supposed to be an excited state absorption from a hitherto unidentified intermediate state. This state is likely to be related with V4+ and/or V3+ ions whose presence in YVO4 is generally recognized. The material may have a potential as a tunable source of blue radiation provided a way is found to increase the ground state absorption.

Effect of temperature on spectroscopic features relevant to laser performance of YVO_4:Er^3+ and GdVO_4:Er^3+ crystals

Optical spectra and luminescence decay curves were measured for erbium-doped YVO(4) and GdVO(4) single crystals as a function of temperature in the 300 K-670 K temperature region. In spite of structural similarity the two systems studied display significantly different transition intensities and nonradiative relaxation rates. It was found in particular that the intensity of parasitic upconverted emission excited at 978 nm depends weakly on temperature for YVO(4):Er(3+), whereas it decreases monotonously with increasing temperature for GdVO(4):Er(3+) and becomes negligibly small at 670 K. It was concluded that GdVO(4):Er(3+) may be a promising laser active material operating at high thermal loading conditions encountered in high-power diode-pumped IR lasers.

Spectroscopic properties of Yb-doped CaF2–YF3 solid-solution laser crystal

The spectroscopic properties of Yb:CaF2–YF3 disordered crystals obtained by the vertical Bridgman method were studied. The 3 at.% Yb, 3 at.% Y:CaF2 crystal absorption cross section σabs centered at 974 nm reached 7.2 × 10−21 cm2 and the fluorescence lifetime was 3.54 ms at room temperature. Experimental results show that co-doping Y3+ ions at different Y:Yb ratios can modulate the spectroscopy and lengthen the luminescence lifetime of Yb3+ ions in the CaF2 lattice. There are three main kinds of lattice in the 3 at.% Yb, 3 at.% Y:CaF2 crystal, as concluded from the low-temperature spectra.