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We report on a detailed spectroscopic study of Eu 3+ ions in the monoclinic KYb(WO 4 ) 2 crystal. The polarized room and low-temperature absorption spectra are measured. The maximum σ abs corresponding to the 7 F 1 → 5 D 1 transition is 1.32×10 –20 cm 2 at 534.2 nm with a bandwidth of 0.7 nm (for E || N m ). The Stark sub-levels of the excited mulitplets are determined. A Judd-Ofelt analysis is applied to the Eu 3+ :KYb(WO 4 ) 2 crystal to determine the probability of spontaneous transitions, radiative lifetimes and luminescence branching ratios. Within the strong configuration interaction (SCI) approximation, the intensity parameters are Ω 2 =4.757, Ω 4 =2.295, Ω 6 =1.644 [10 –20 cm 2 ] and Δ f =50160 cm –1 . The radiative lifetime of the 5 D 0 state is 351 µs. The maximum stimulated-emission cross-section corresponding to the 7 F 1 → 5 D 1 transition is 1.44×10 –20 cm 2 at 703.2 nm (for E || N m ). Under UV excitation, the Eu 3+ :KYb(WO 4 ) 2 crystal provides intense red photoluminescence with CIE coordinates, x=0.675, y=0.325. [ABSTRACT FROM AUTHOR]

We report on growth and detailed spectroscopic study of Eu 3+ -doped tetragonal sodium gadolinium double tungstate, Eu:NaGd(WO 4 ) 2 , a new promising crystal for deep-red lasers. Large-volume crystal doped with 4.9 at.% Eu is grown by Czochralski method along the [001] crystallographic direction. Absorption of Eu 3+ ions is studied at room temperature (RT) and at 6 K. For the absorption band related to the 7 F 1 → 5 D 1 transition suitable for pumping of Eu:NaGd(WO 4 ) 2 , the maximum cross-section is σ abs = 1.2 × 10 −21 cm 2 at 535.5 nm with the full width at half maximum (FWHM) of 3.1 nm (at RT, for E || a polarization). For the 5 D 0 → 7 F 4 transition, the maximum stimulated-emission cross-section is σ SE = 1.6 × 10 −21 cm 2 at 698.3 nm (RT, E || c polarization). Lifetime of the 5 D 0 state is 490 ± 10 μs (at RT). Under UV excitation, Eu:NaGd(WO 4 ) 2 provides intense red emission with CIE coordinates ( x = 0.671, y = 0.329). [ABSTRACT FROM AUTHOR]

We report on a comprehensive spectroscopic and laser characterization of monoclinic Yb,Tm:KLu(WO 4 ) 2 crystals. Stimulated-emission cross-section spectra corresponding to the 3 F 4 → 3 H 6 transition of Tm 3+ ions are determined. The radiative lifetime of the 3 F 4 state of Tm 3+ ions is 0.82 ms. The maximum Yb 3+ → Tm 3+ energy transfer efficiency is 83.9% for 5 at.% Yb – 8 at.% Tm doping. The fractional heat loading for Yb,Tm:KLu(WO 4 ) 2 is 0.45 ± 0.05. Using a hemispherical cavity and 5 at.% Yb – 6 at.% Tm doped crystal, a maximum CW power of 227 mW is achieved at 1.983–2.011 μm with a maximum slope efficiency η = 14%. In the microchip laser set-up, the highest slope efficiency is 20% for a 5 at.% Yb– 8 at.% Tm doped crystal with a maximum output power of 201 mW at 1.99–2.007 μm. Operation of Yb,Tm:KLu(WO 4 ) 2 as a vibronic laser emitting at 2.081–2.093 μm is also demonstrated. [ABSTRACT FROM AUTHOR]

We report on a comprehensive spectroscopic study of monoclinic Eu:KLu(WO 4 ) 2 crystal concerning its potential applications in red lasers. Optical absorption and stimulated-emission cross-section spectra are determined for this crystal for the principal light polarizations, E || N p , N m and N g . The maximum σ SE corresponding to the 5 D 0 → 7 F 4 transition is 1.78×10 −2 0 cm 2 at 703.5 nm (for E || N m ). Spectroscopic properties of Eu:KLu(WO 4 ) 2 are modeled within the conventional Judd–Ofelt theory, as well as its modification for systems with an anomalously strong configuration interaction (ASCI), yielding absorption oscillator strengths, luminescence branching ratios for 5 D J → 7 F J ' transitions and radiative lifetimes of the 5 D J states. Photoluminescent properties of Eu:KLu(WO 4 ) 2 are studied under UV/visible excitation. Polarized Raman spectra are measured for Eu:KLu(WO 4 ) 2 . [ABSTRACT FROM AUTHOR]

Abstract: The analytical expressions for thermo-optic coefficients, dn/dT, for “fast” and “slow” light waves propagating along the arbitrary direction in a biaxial crystal are derived. On the basis of these expressions, the all-space analysis of existence of athermal directions is performed for monoclinic and biaxial KY(WO4)2 at 1.03μm. The calculations are performed for an arbitrary light propagation direction and polarization (not restricted to the principal planes). The appearance of directions that can be athermal for both “fast” and “slow” waves is predicted. The dispersion of athermal directions is analyzed for visible and near-IR. The existence of upper and lower dispersion limits for athermal behavior of KY(WO4)2 is shown. It is shown that the optical indicatrix axes can be athermal itself at some light wavelengths. Wavelength- and temperature-dependent position of the optical axes of KY(WO4)2 is also determined. [Copyright &y& Elsevier]

Abstract: Monoclinic 2at% Eu-doped KY(WO4)2 is grown by top-seeded solution growth method. Polarization-resolved absorption and stimulated-emission cross-section spectra are determined for this crystal. Spectroscopic properties of Eu:KY(WO4)2 are modeled within conventional Judd–Ofelt theory, as well as theory of f–f transition intensities for systems with anomalously strong configuration interaction, yielding absorption oscillator strengths, luminescence branching ratios and radiative lifetime of 5D0 state. The impact of excited-state absorption from this state on possibility of laser operation is discussed. Photoluminescent properties of Eu:KY(WO4)2 are determined. This crystal provides intense red emission with CIE coordinates x=0.670, y=0.329. [Copyright &y& Elsevier]

Monoclinic Ho:KY(WO 4 ) 2 crystals doped with up to 7.5 at.% Ho are grown by the Top Seeded Solution Growth-Slow Cooling method. The evolution of their unit cell parameters in dependence on the Ho doping and temperature is studied. The polarized low-temperature (6 K) optical absorption of the Ho 3+ ion is investigated in detail to determine the energy of the Stark sub-levels. Room-temperature absorption, stimulated-emission and gain cross-section spectra of Ho:KY(WO 4 ) 2 crystals are derived for polarizations parallel to the principal optical axes, E || N p , N m and N g . The maximum absorption cross-section for the 5 I 8 → 5 I 7 transition is 1.60×10 −20 cm 2 at 1961.0 nm and the maximum stimulated-emission cross-section for the 5 I 7 → 5 I 8 transition is 2.65×10 −20 cm 2 at 2056.3 nm (for E || N m ). The radiative lifetime of the upper laser level of the Ho 3+ ion ( 5 I 7 ) amounts to 4.8 ms. Continuous-wave Ho 3+ laser operation is achieved under in-band pumping by a Tm laser at 1946 nm. In the microchip configuration, the maximum output power reached 205 mW at 2105 nm with a slope efficiency as high as 85%. [ABSTRACT FROM AUTHOR]