R. Lisiecki

Rare earth-doped lead borate glasses and transparent glass–ceramics: Structure–property relationship

Correlation between structure and optical properties of rare earth ions in lead borate glasses and glass-ceramics was evidenced by X-ray-diffraction, Raman, FT-IR and luminescence spectroscopy. The rare earths were limited to Eu(3+) and Er(3+) ions. The observed BO(3)↔BO(4) conversion strongly depends on the relative PbO/B(2)O(3) ratios in glass composition, giving important contribution to the luminescence intensities associated to (5)D(0)-(7)F(2) and (5)D(0)-(7)F(1) transitions of Eu(3+). The near-infrared luminescence and up-conversion spectra for Er(3+) ions in lead borate glasses before and after heat treatment were measured. The more intense and narrowing luminescence lines suggest partial incorporation of Er(3+) ions into the orthorhombic PbF(2) crystalline phase, which was identified using X-ray diffraction analysis.

Conversion of infrared radiation into visible emission in YVO4 crystals doped with ytterbium and holmium

Conversion of the infrared (IR) radiation at 975 nm into the visible emission in the Czochralski grown YVO4 crystals containing several different concentrations of Yb3+ and Ho3+ has been investigated. Unlike other matrices doped with ytterbium and holmium, the YVO4:Yb,Ho system exhibits intense red upconverted emission originating from the F55 level, whereas, green upconverted emission originating from the S25 level of Ho3+ is found to be unusually weak at room temperature but dominating at 4.2K. Power dependencies of the emissions are consistent with two-step excitation process but time dependencies differ and imply that the longlived I75 level of Ho3+ is involved in the second-step excitation of red emission. Intensity distribution of σ-polarized emission band associated with the F55-I85 transition with peak value of effective stimulated emission cross section amounting to 10−20cm2 combined with the possibility of tailoring of optical pumping efficiency by appropriate choice of dopant concentrations off...

Laser spectroscopy of rare earth ions in lead borate glasses and transparent glass-ceramics

Rare earth doped lead borate glasses and transparent glass-ceramics have been studied using optical spectroscopy. Based on the absorption, emission and its decay and the Judd-Ofelt calculations, several radiative and laser parameters for Ln3+ (Ln = Pr, Nd, Eu, Dy, Er, Tm) were evaluated. The large values of luminescence lifetime, quantum efficiency of excited state and room temperature peak stimulated emission cross-section suggest efficient laser transitions of Ln3+ ions in lead borate glasses. The obtained results indicate that lead borate glasses and glass-ceramics containing Ln3+ ions are promising host matrices for solid-state laser applications.

Optical losses in YVO4: RE (RE = Nd3+, Er3+, Tm3+) laser crystals

The relevance of processes contributing to depletion of pump and upper laser levels has been assessed based on experimental data obtained during measurement of excited state absorption, steady state emission and dynamics of excited states as a function of excitation power and activator concentration. It has been concluded that the excited state absorption in YVO4: Nd and YVO4: Er is not significant except for that from the 4I11/2 level of Er3+. In these systems, the interionic processes are dominant. In particular, the reported decrease of the YVO4: Er laser slope efficiency when the Er3+ concentration increased from 0.5 to 1 at % is due mainly to the up-conversion by energy transfer from the pump level and upper laser level. Excited state absorption cannot contribute to depletion of excited states involved in the 3F4-3H6 laser operation near 1800 nm in the YVO4: Tm crystal. However, the heavy doping required to enhance the cross-relaxation process which feeds the upper laser level brings about the migration-accelerated energy transfer to energy sinks.

Energy transfer processes from Yb3＋ to Ln3＋ （Ln=Er or Tm） in heavy metal glasses

Abstract Heavy metal glasses doubly doped with Yb 3+ and Ln 3+ ions (Ln=Er or Tm) were studied. Glass host matrices were limited to lead borate glass and lead germanate glass. Efficient resonant (Yb 3+ -Er 3+ ) and non-resonant (Yb 3+ -Tm 3+ ) energy transfer was observed for the studied systems. Near-infrared luminescence spectra at 1.53 μm (Er 3+ ) and 1.9 μm (Tm 3+ ) were detected under excitation of Yb 3+ by 975 nm diode laser line. They corresponded to 4 I 13/2 → 4 I 15/2 (Er 3+ ) and 3 F 4 → 3 H 6 (Tm 3+ ) transitions of rare earth ions, respectively. The unusual large spectral linewidth nearly close to 110 nm for 4 I 13/2 → 4 I 15/2 transition of Er 3+ ions in lead borate glass was obtained, whereas long-lived near-infrared luminescence at 1.53 μm was detected in lead germanate glass. Quite different situation was observed for Yb 3+ -Tm 3+ doubly doped glasses. In contrast to lead borate glass, near-infrared ( 3 F 4 → 3 H 6 ) luminescence spectra were registered for Tm 3+ ions in lead germanate glasses, only. These phenomena strongly depended on stretching vibrations of glass host, which was confirmed by FT-IR spectroscopy.

Up-conversion processes of rare earth ions in heavy metal glasses

Abstract Heavy metal lead germanate glasses doubly doped with Yb 3+ and Ln 3+ ions (Ln=Er, Tm) were investigated. Up-conversion spectra of Er 3+ and Tm 3+ were registered under diode-laser excitation of Yb 3+ . Up-conversion luminescence bands corresponded to 4 S 3/2 → 4 I 15/2 (green) and 4 F 9/2 → 4 I 15/2 (red) transitions of Er 3+ as well as 1 G 4 → 3 H 6 (blue) and 3 H 4 → 3 H 6 (NIR) transitions of Tm 3+ , respectively.

Effect of substitution of lutetium by gadolinium on emission characteristics of (Lu x Gd 1-x ) 2 SiO 5 : Sm 3+ single crystals

Single crystals of (LuxGd1-x)2SiO5:Sm (0.5 at%) with x = 0.19 (81% Gd3+) and x = 0.11 (89% Gd3+) belonging respectively to the C2/c and P21/c space groups were grown by the Czochralski method under nitrogen atmosphere. Detailed investigation of their spectroscopic properties were performed with the aim of understanding the effect of structural modification on emission characteristics of incorporated Sm3+ ions with a special attention directed to a laser potential associated with yellow emission line. It was inferred from low temperature optical spectra that almost all emission intensity in the host with C2/c symmetry comes from one of two available Sm3+ sites, whereas two Sm3+ sites contribute to emission in the host with P21/c symmetry. Excitation spectra of Sm3+ emission recorded in the VUV-UV region between 100 nm and 350 nm made it possible to locate the energy of CT transition at about 6.11 eV and to assess the low energy limit for the 4f5→ 4f45d1 transitions of Sm3+ to about 6.81 eV. It implies that in the two systems studied these energies are advantageously high thereby preventing the contribution of intense allowed transitions to an adverse excited state absorption of both blue pump radiation and yellow emission. Experiments of optical amplification of yellow emission were performed employing a pump-and-probe technique in order to verify this implication. It was found that for a LGSO:Sm3+ crystal having the C2/c symmetry an increase of the pump power density from 20 mJ/cm2 to 50 mJ/cm2 at a constant power probe density of 150 μW/cm2 brings about a positive gain growing from about 0.25 to 2 [cm−1]. In the same conditions a maximum gain value of 1 cm−1 was measured for LGSO:Sm3+ crystal having the P21/c symmetry. It was concluded that the former system is promising for the design of all-solid-state yellow lasers.

Optical spectroscopy of Nd-doped borate glasses

Optical absorption, luminescence excitation and emission spectra as well as luminescence kinetics of the Nd³⁺ centres in glasses with Li<inf>2</inf>B<inf>4</inf>O<inf>7</inf>:Nd, LiCaBO<inf>3</inf>:Nd, and CaB<inf>4</inf>O<inf>7</inf>:Nd compositions containing 0.5 and 1.0 mol. % Nd<inf>2</inf>O<inf>3</inf> have been investigated and analyzed. Using Judd-Ofelt theory oscillator strengths (f) and phenomenological intensity parameters Ω<inf>t</inf> (Ω<inf>2</inf>, Ω<inf>4</inf>, and Ω<inf>6</inf>) for all investigated glasses were determined. Radiative transitions rates (W<inf>r</inf>), radiative lifetimes (τ<inf>rad</inf>), and branching ratios (β) for Nd³⁺ centres have been calculated. Measured lifetimes for Nd³⁺ centres in the ⁴F<inf>3/2</inf> emitting level are compared with those calculated and quantum efficiency (η) have been estimated.

Spectroscopic investigation and DFT modelling studies of Eu 3+ complex with 1-(2,6-dihydroxyphenyl)ethanone

Eu3+ complex with 1-(2,6-dihydroxyphenyl)ethanone in the solid state has been synthesized and characterized by elemental analysis, UV-visible, FT-IR and FT-Raman spectroscopies, powder X-ray diffraction, electron emission under femtosecond laser excitation. The stoichiometry and the formula of the studied complex have been proposed. Its physicochemical properties have been analyzed in terms of the structure and DFT calculations performed for the ligand. The luminescence and dynamics of the excited states depopulation have been studied using femtosecond laser excitation. Spectral and energetic transformation of femtosecond light impulses has been studied and possibility of the energy transfer between the ligand and the Eu3+ electron levels has been analyzed.

Optical properties of crystals doped with Sm3+ or Dy3+ relevant to potential InGaN/GaN laser diode-pumped visible laser operation: A comparative study

Results of detailed spectroscopic investigation of Sm3+ and Dy3+ ions incorporated in crystal structures of Yal YAl3(BO3)4, LiNbO3, Gd3Ga5O12, Gd2SiO5, Lu2SiO5 and (Gd, Lu)2SiO5 are reported and discussed. The impact of the hosts on transition intensities and excited state relaxation dynamics of incorporated luminescent ions was examined. Distribution of luminescence intensity among spectral bands in terms of luminescence branching ratios was evaluated based on numerical integration of luminescence bands. Intensities of UV and blue absorption bands potentially useful for optical pumping were determined quantitatively in units of absorption cross section. The most intense luminescence bands related to potential laser transitions 4G5/2 → 6H7/2 of Sm3+ around 600 nm and 4F9/2 → 6H13/2 of Dy3+ around 580 nm were calibrated in units of emission cross section. Evaluated peak values of emission cross section range from 0.43 × 10−20 cm2 for Sm3+ in (Gd, Lu)2SiO5 to 1.17 × 10−20 cm2 for Sm3+ in LiNbO3. Those for dysprosium-doped crystals range from 0.63 × 10−20 cm2 for LiNbO3:Dy3+ to 2.0 × 10−20 cm2 for Yal YAl3(BO3)4:Dy3+. It follows from these considerations that samarium-doped crystals show promise for laser application owing to the combination of a strong absorption that matches radiation of commercial laser diodes emitting near 405 nm and long luminescence lifetime. Major shortcoming of dysprosium-doped crystals results from a weak intensity of absorption bands available for optical pumping near 450 nm and 385 nm combined with relatively strong self-quenching of luminescence.