Correction for ‘A roadmap for laser optimization of Yb:Ca3(NbGa)5O12-CNGG-type single crystal garnets’ by J. O. Álvarez-Pérez et al., J. Mater. Chem. C, 2021, 9, 4628–4642, DOI: 10.1039/d0tc05718e.

Correction for 'A roadmap for laser optimization of Yb:Ca-3(NbGa)(5)O-12-CNGG-type single crystal garnets' by J. O. alvarez-Perez et al., J. Mater. Chem. C, 2021, 9, 4628-4642, DOI: 10.1039/d0tc05718e.

Magnetic-dipole photoluminescence from octahedral Yb3+ in CaNbGa garnet is proposed for sensing the magnetic component of plasmonic radiated fields.

Yb and Er codoped NaT(XO4)2 (T = Y, La, Gd, Lu and X = Mo, W) disordered oxides show a green (Er3+ related) up-conversion (UC) efficiency comparable to that of Yb:Er:β-NaYF4 compound and unless 3 times larger UC ratiometric thermal sensitivity. The similar UC efficiency of Yb:Er doped NaT(XO4)2 and β-NaYF4 compounds allowed testing equal subcutaneous depths of ex-vivo chicken tissue in both cases. This extraordinary behavior for NaT(XO4)2 oxides with large cutoff phonon energy (ħω≈ 920 cm-1) is ascribed to 4F9/2 electron population recycling to higher energy 4G11/2 level by a phonon assisted transition. Crystalline nanoparticles of Yb:Er:NaLu(MoO4)2 have been synthesized by sol-gel with sizes most commonly in the 50-80 nm range, showing a relatively small reduction of the UC efficiency with regards to bulk materials. Fluorescence lifetime and multiphoton imaging microscopies show that these nanoparticles can be efficiently distributed to all body organs of a perfused mouse.

Yb and Er codoped NaT(XO4)2 (T = Y, La, Gd, Lu and X = Mo, W) disordered oxides show a green (Er3+ related) up-conversion (UC) efficiency comparable to that of Yb:Er:β-NaYF4 compound and unless 3 times larger UC ratiometric thermal sensitivity. The similar UC efficiency of Yb:Er doped NaT(XO4)2 and β-NaYF4 compounds allowed testing equal subcutaneous depths of ex-vivo chicken tissue in both cases. This extraordinary behavior for NaT(XO4)2 oxides with large cutoff phonon energy (ħω≈ 920 cm-1) is ascribed to 4F9/2 electron population recycling to higher energy 4G11/2 level by a phonon assisted transition. Crystalline nanoparticles of Yb:Er:NaLu(MoO4)2 have been synthesized by sol-gel with sizes most commonly in the 50–80 nm range, showing a relatively small reduction of the UC efficiency with regards to bulk materials. Fluorescence lifetime and multiphoton imaging microscopies show that these nanoparticles can be efficiently distributed to all body organs of a perfused mouse.

The spectral contributions to the Yb3+ bandwidth in CNGG-type laser crystals have been disclosed by combining 6 K spectroscopy, knowledge of their crystal structures and CF modeling of Yb3+ energy levels.

Yb and Er codoped NaT(XO4)2 (T = Y, La, Gd, Lu and X = Mo, W) disordered oxides show a green (Er3+ related) up-conversion (UC) efficiency comparable to that of Yb:Er:β-NaYF4 compound and unless 3 times larger UC ratiometric thermal sensitivity. The similar UC efficiency of Yb:Er doped NaT(XO4)2 and β-NaYF4 compounds allowed testing equal subcutaneous depths of ex-vivo chicken tissue in both cases. This extraordinary behavior for NaT(XO4)2 oxides with large cutoff phonon energy (ħω≈ 920 cm-1) is ascribed to 4F9/2 electron population recycling to higher energy 4G11/2 level by a phonon assisted transition. Crystalline nanoparticles of Yb:Er:NaLu(MoO4)2 have been synthesized by sol-gel with sizes most commonly in the 50-80 nm range, showing a relatively small reduction of the UC efficiency with regards to bulk materials. Fluorescence lifetime and multiphoton imaging microscopies show that these nanoparticles can be efficiently distributed to all body organs of a perfused mouse.

Yb and Er codoped NaT(XO4)(2) (T = Y, La, Gd, Lu and X = Mo, W) disordered oxides show a green (Er3+ related) up-conversion (UC) efficiency comparable to that of Yb:Er:beta-NaYF4 compound and unless 3 times larger UC ratiometric thermal sensitivity. The similar UC efficiency of Yb:Er doped NaT(XO4)(2) and beta-NaYF4 compounds allowed testing equal subcutaneous depths of ex-vivo chicken tissue in both cases. This extraordinary behavior for NaT (XO4)(2) oxides with large cutoff phonon energy (h omega approximate to 920 cm(-1)) is ascribed to F-4(9/2) electron population recycling to higher energy (4)G(11/2) level by a phonon assisted transition. Crystalline nanoparticles of Yb:Er:NaLu(MoO4)(2) have been synthesized by sol-gel with sizes most commonly in the 50-80 nm range, showing a relatively small reduction of the UC efficiency with regards to bulk materials. Fluorescence lifetime and multiphoton imaging microscopies show that these nanoparticles can be efficiently distributed to all body organs of a perfused mouse.

The Na+-Yb+ (or Er3+) co-substitution of Ca2+ in Ca(3)Nb(1.)5Ga(3.5)O(12) (CNGG) laser crystal is studied. In contrast to other garnets whose structural disorder is exclusively based on the presence of differently sized cations on the same crystal sites, Na+ incorporated in the dodecahedral site (a site also shared by Ca2+ and trivalent lanthanides) creates diverse electric charge distributions over the dodecahedral sublattice, which adds to the disorder associated with Nb5+ and Ga3+ simultaneous occupation of the octahedral and tetrahedral sites. The currently determined cationic compositions of Czochralski grown congruent CNGG and Na-modified CNGG crystals show that Na+ incorporation reduces the cationic vacancy concentration on dodecahedral and octahedral sites but does not affect that in tetrahedral sites. Physical properties of interest for laser design (optical transmission, elastic constants, hardness, specific heat, thermal conductivity, thermal expansion, refractive index dispersion, group velocity dispersion, and thermo optic coefficients) have been systematically determined at cryogenic temperatures and above room temperature. Na+ incorporation into CNGG decreases the crystal growth temperature, promotes Yb3+ doping, and importantly, increases the Yb3+ optical bandwidth, offering good prospects for the implementation of ultrashort pulses in mode-locked laser oscillators.

Thermo-optic coefficients dn o/dT and dn e/dT were measured in tetragonal double tungstate and double molybdate crystals NaT(XO4)2 (where T = Y, La, Gd or Bi and X = W or Mo) by a laser beam deviation method in the spectral range 0.4–1.1 μm. Thermal expansion coefficients in the directions of a and c crystallographic axes were also measured. Analytical expressions for thermo-optic dispersion formulas were derived as series in 1/λ 2. All dn/dT values for NaT(XO4)2 crystals were found to be negative. Their absolute values satisfy the relation |dn e/dT| > |dn o/dT| for crystals without Bi and |dn o/dT| > |dn e/dT| for crystals with Bi. A clear tendency for dn/dT values to decrease with the increase of the volumetric thermal expansion coefficient α vol of the crystal was observed. This is related with dominant contribution of volumetric thermal expansion effect to the temperature dependence of the refractive index. Thermal coefficients of the optical path W = dn/dT + (n − 1)α T governing thermal lensing effect were calculated for different light propagation directions and polarizations as well as crystal athermal directions.

Undoped and Er-doped NaY(WO4)2 disordered single crystals have been grown by the Czochralski technique. The specific heat and thermal conductivity (κ) of these crystals have been characterized from T = 4 K to 700 K and 360 K, respectively. It is shown that κ exhibits anisotropy characteristic of single crystals as well as a κ(T) behavior observed in glasses, with a saturation mean free phonon path of 3.6 Å and 4.5 Å for propagation along a and c crystal axes, respectively. The relative energy positions and irreducible representations of Stark Er(3+) levels up to (4)G(7/2) multiplet have been determined by the combination of experimental low (<10 K) temperature optical absorption and photoluminescence measurements and simulations with a single-electron Hamiltonian including both free-ion and crystal field interactions. Absorption, emission and gain cross sections of the (4)I(13/2)↔(4)I(15/2) laser related transition have been determined at 77 K. The (4)I(13/2) Er(3+) lifetime (τ) was measured in the temperature range of 77-300 K, and was found to change from τ (77K) ≈ 4.5 ms to τ (300K) ≈ 3.5 ms. Laser operation is demonstrated at 77 K and 300 K by resonantly pumping the (4)I(13/2) multiplet at λ≈1500 nm with a broadband (FWHM≈20 nm) diode laser source perfectly matching the 77 K crystal (4)I(15/2) → (4)I(13/2) absorption profile. At 77 K as much as 5.5 W of output power were obtained in π-polarized configuration with a slope efficiency versus absorbed pump power of 57%, the free running laser wavelength in air was λ≈1611 nm with the laser output bandwidth of 3.5 nm. The laser emission was tunable over 30.7 nm, from 1590.7 nm to 1621.4 nm, for the same π-polarized configuration.

Color-defect-free 5 at.% Tm:NaGd(MoO4)(2) crystals have been grown in a Na2MoO4/Na2Mo2O7 flux. Using a hemispherical optical cavity and pumping at lambda = 794.5 nm with a Ti-sapphire laser, up to 850 mW of output power at lambda approximate to 1900 nm was obtained at 300 K with an output coupler transmission of 8%. In the cw regime, the slope efficiency versus absorbed power was eta = 45% and the pump power laser threshold was approximate to 180 mW. The laser was tunable from 1875 to 1975 nm and the emission had a FWHM bandwidth approximate to 20 nm, indicating the potential for ultrashort laser pulse generation.

We report crystal growth, spectroscopy and eye-safe laser operation of Er3+-doped disordered NaY(WO4)2 crystal. It is shown that crystalline disorder facilitates efficient direct resonant pumping around 1500 nm by the wideband InGaAsP/InP laser diode sources.

Sellmeier parameters of thirteen tetragonal (space group \(I\overline{4}\)) double tungstate and double molybdate laser crystals with M+T3+(X6+O4)2 composition have been calculated using the room temperature refractive indices determined from the ultraviolet band gap of the crystals to λ≈2 μm. All considered crystals are uniaxial but only crystals with Bi in their composition show a significant birefringence (Δn>10−2). The refractive index value increases for the sequence T3+=La, Y, Gd, Lu, and Bi independently of the M+ and X6+ cation pair. Implications for the design of laser waveguides and laser pulse dispersion are discussed.

5 at% Tm-doped NaGd(MoO4)2 laser crystal operated in CW conditions provided up to 641 mW of output power at λ ≈ 1910 nm with a slope efficiency of 50.8% and a pump power laser threshold of 166 mW. 10 at% Tm-doped Li3Ba2Lu3(MoO4)8 laser operated in quasi-CW conditions provided up to 510 mW of output power at λ ≈ 1950 nm with a slope efficiency of 71.4% and a pump power laser threshold of 125 mW. Both crystals were grown by the Top Seeded Solution Growth method at about two hundreds degrees below their melting points. The structural disorder of these crystals confers inhomogenous broadening to the Tm3+ electronic transitions. Slightly broader laser tuning range and laser emission bandwidths are observed in the Li3Ba2Lu3(MoO4)8 crystal despite of the lower expected degree of crystalline disorder. The crystals are promising for the development of mode locked ultrafast (fs) lasers with emission close to λ = 2 μm.

Tetragonal double tungstate single crystals with formula NaT(WO4)(2) have been grown by the Czochralski (T = Gd, La, Y) or by the top-seeded solution growth (T = Lu) methods with Tm concentration between 8 x 10(18) and 7.85 x 10(20) cm(-3). The spectroscopic properties of Tm3+ in these crystals are related with the peculiarities of their I (4) over bar crystalline structure. Sixty-five percent of La ions in NaLa(WO4)(2) are in the 2d site, while in the other crystal hosts, the lanthanide occupies preferentially the 2b site (59% in T = Gd, 74% in T = Y, and 58% in T = Lu). As a consequence, the linewidths of spectral bands associated with the electronic transitions are significantly narrower in NaLa(WO4)(2) than in the rest of the isostructural crystals considered. Polarized spectroscopic measurements at 5 K and at higher temperatures, along with energy level simulation of the 4f(12) configuration using a single-electron Hamiltonian, including free-ion and crystal field interactions, allowed us to determine the irreducible representation and energy of Stark levels up to the P-3(0) multiplet and thus to obtain realistic partition functions (Z) used for emission cross-section calculations. In particular, for the F-3(4)(u) -> H-3(6)(l) laser transition at lambda approximate to 2 mu m, this provides: Z(l)/Z(u) = 1.436 (T = Gd), 1.464 (T = La), 1.448 (T = Y), and 1.471 (T = Lu). Radiative lifetimes calculated by the Judd-Ofelt and Fuchtbauer-Ladenburg methods are in agreement and decrease in the following order T = Gd, La, Y, and Lu, however, nonradiative losses are stronger for T = Gd and La crystals; therefore, experimental lifetimes of D-1(2), (1)G(4), H-3(4), and F-3(4) Tm3+ multiplets do not change too much with crystal host. For 4.68 at.% Tm:NaY(WO4)(2) crystal continuous-wave laser operation is obtained with approximate to 42% of slope efficiency and a record (for this crystal class) tuning capability of lambda = 1847-2069 nm. The broad bandwidths, Delta lambda(FWHM) > 20 nm, of the free-running laser emission are promising for ultrafast (fs) mode-locked laser operation near lambda approximate to 2 mu m.

The Tm3+ laser efficiency of NaGd(MoO4)2 crystals (η=50.8%, Pout=641mW) grown in Na2MoO4/Na2Mo2O7 flux is larger than that obtained in similar Czochralski-grown crystals annealed to eliminate color centers.

Liquid-phase epitaxial growth of Yb3+ doped NaGd (WO4)(2) crystalline layers has been obtained on Y modified NaGd(WO4)(2) Czochralski grown single crystal substrates. It is shown that the lattice parameter of the layer and substrate can be equalized by proper selection of the Yb and Y compositions. The epitaxial layers obtained are highly transparent, with thicknesses in the range 10-70 mu m, and with crystallographic quality close to that of the used substrates. The spectroscopic properties of Yb3+ in the layer are anisotropic and similar to those of Yb-doped NaGd(WO4)(2) single crystals. The layers are envisaged as optical gain media for the design of ultrafast mode-locked thin disk lasers.

We report what is believed to be the first resonantly pumped laser operation based on Er(3+)-doped disordered double tungstate single crystal. Efficient laser operation of an Er(3+):NaY(WO(4))(2) laser at ∼1609.6 nm was demonstrated with the naturally wideband, ∼20 nm, InGaAsP/InP laser diode pumping at ∼1501 nm. Laser wavelength tunability of ∼34 nm was also demonstrated based on disorder-broadened emission features of Er(3+):NaY(WO(4))(2) single crystal.