S. E. Ivanova

Spectroscopic studies of erbium-doped potassium-lead double chloride crystals KPb2Cl5:Er3+: 1. Optical spectra and relaxation of excited states of the erbium ion in potassium-lead double chloride crystals

Optical spectra, intensities of radiative and nonradiative transitions, and luminescence kinetics in erbium-doped potassium-lead double chloride crystals KPb2Cl5:Er3+s(KPC:Er3+) were investigated. The crystals were grown by the Bridgman-Stockbarger method. Their absorption and luminescence spectra were studied experimentally. The crystal-matrix absorption edge was determined at 80 and 300 K. Intensity parameters, radiative transition probabilities, branching ratios, and nonradiative relaxation rates were estimated by the Judd-Ofelt method. The luminescence kinetics from the emitting levels 4G11/2, 2G9/2, 4S3/2, and 4F9/2 upon selective excitation was studied.

New low-phonon frequency crystals based on rare-earth-doped double halogenides for multiwavelength diode-pumped solid state lasers

Energy (frequency) of phonons is the main parameter which determines ratio between probabilities of radiative and radiationless transitions in luminescence. Single crystals of double chlorides KPb2C15 and bromides KPb2Br5 , which are formed by heavy ions and have a low energy phonon spectrum (h? <200 and 150 cm-1, respectively), of optical quality were obtained using the Bridgmen-Stockbarger technique. We studied the optical spectra and luminescence kinetics of RE —doped crystals (RE= Pr3+, Nd3+, Tb3+, Ho3+, Er3+ etc). Intensity parameters were determined by the Judd-Ofelt method, radiative and non-radiative transition probabilities were calculated. It was shown that low multiphonon relaxation rate in these crystals together with high values of radiative probabilities leads to the evidence of high intensity luminescence in spectral domain from 360 to 9000 nm. These features make these crystals promising for practical applications as active media for UV, VIS and mid-IR solid state lasers and amplifiers with laser diode pumping.

Spectroscopic study of neodymium-doped potassium-lead double chloride Nd3+:KPb2Cl5 crystals

Optical spectra, radiative and nonradiative transition intensities, and luminescence kinetics of neodymium-doped potassium-lead double chloride crystals Nd3+:KPb2Cl5, (Nd3+:KPC) are investigated. Crystals were grown by the Stockbarger-Bridgman technique. Experimental studies of absorption and luminescence spectra are performed, intensity parameters are obtained by the Judd-Ofelt method, radiative transition probabilities and branching ratios are calculated, and nonradiative transition probabilities are estimated. Luminescence kinetics of 2K13/2, 2P3/2, and 4D3/2 radiative levels of neodymium under selective excitation in the 355-nm region are studied.

Spectroscopic study of thulium-activated double sodium yttrium fluoride Na0.4Y0.6F2.2:Tm3+ crystals: I. Intensity of spectra and luminescence kinetics

Na0.4Y0.6F2.2:Tm3+ crystals with a thulium content from 1 to 100 at % have been grown by the Stockbarger-Bridgman method. The optical spectra of Na0.4Y0.6F2.2:Tm3+ crystals were investigated in detail at room and low (10 K) temperatures, and the luminescence kinetics was analyzed using different excitation methods. The structure of the Stark splitting of thulium levels as “quasi-centers,” characterized by inhomogeneous broadening of the Stark components, is determined from analysis of the absorption spectrum at 10 K. The oscillator strengths of the transitions from the ground state to excited multiplets are determined from the absorption cross-section spectra at 300 K for ten transitions in the range 5000–38 500 cm−1 and seven transitions in the range 5000–28 500 cm−1. The transition intensity parameters Ωt, obtained by the Judd-Ofelt method from the spectra due to the transitions to ten and seven excited levels, were found to be, respectively, (i) Ω2 = 1.89 × 10−20, Ω4 = 2.16 × 10−20, and Ω6 = 1.40 × 10−20 cm2 and (ii) Ω2 = 2.04 × 10−20, Ω4 = 2.01 × 10−20, and Ω6 = 1.44 × 10−20 cm2. These values of the intensity parameters were used to calculate the radiative transition probabilities and branching ratios and to estimate the multiphonon nonradiative transition probabilities for NYF:Tm. The luminescence decay kinetics from thulium radiative levels upon their selective excitation by nanosecond laser pulses has been studied and the lifetimes of thulium radiative levels in NYF crystals have been found.

Spectroscopic properties of TR3+ -doped double chloride crystals

We studied the optical spectra and luminescence kinetics of double chloride Kpb2Cl5:TR3+ crystals as a new luminescent material promising for UV, VIS and mid-IR lasers, pumped with laser diodes. Intensity parameters were determined by the Judd-Ofelt method, radiative and non- radiative transition probabilities were calculated. It is shown that low multiphoton relaxation rate in the se crystal together with high values of radiative probabilities leads to the evidence of high intensive luminescence in spectral domain from 360 to 5000 nm. These features make these crystals promising for practical applications as active media for UV, VIS and mid-IR solid state lasers and amplifiers.

Study of spectroscopic characteristics of holmium-doped double sodium-yttrium fluoride crystals Na0.4Y0.6F2.2:Ho3+

We have grown crystals Na0.4Y0.6F2.2:Ho3+ (NYF:Ho3+) by the Bridgman-Stockbarger method. The optical spectra and luminescence kinetics of NYF:Ho3+ crystals have been studied. Based on the analysis of low-temperature absorption spectra, we determine the structure of the Stark splitting of holmium levels in NYF:Ho3+ crystals. From absorption spectra examined at T = 300 K, we calculate absorption cross-section spectra and oscillator strengths of transitions from the ground state of holmium to excited multiplets. We show that the absorption spectra of NYF:Ho3+ crystals consist of broad bands that lie in the UV, visible, and near-IR ranges. The most intense bands are observed in the visible range, they correspond to transitions 5I8 → (5F1, 5G6) and 5I8 → (5F4, 5S2), and their maximal absorption cross sections are σabsmax (λ = 450.3 nm) = 1.16 × 10−20 cm2 and σabsmax (λ = 535.1 nm) = 0.9 × 10−20 cm2. The intensity parameters Ωt have been calculated by the Judd-Ofelt method taking into account 10, 12, and 20 transitions from the 5I8 ground state to excited multiplets. We show that, with an increasing number of transitions taken into account in the calculation, the parameters Ωt somewhat increase. For 20 transitions, we have obtained the following intensity parameters: Ω2 = 0.97 × 10−20, Ω4 = 1.74 × 10−20, and Ω6 = 1.15 × 10−20 cm2. With these parameters, we have calculated the probabilities of radiative transitions, the radiative lifetimes, and the branching ratios. The rates of multiphoton nonradiative transitions have been estimated. The luminescence decay kinetics from excited holmium levels 5F3 (5F4, 5S2) and 5F5 have been studied upon selective excitation in the range of 490 nm, and the lifetimes of these levels have been experimentally determined. We find that the calculated and experimental rates of radiative and nonradiative relaxation from excited holmium levels agree well with each other. We show that, upon pumping in the range of 490 nm, the multiplet (5F4, 5S2) is populated as a result of the radiative and nonradiative excitation relaxation from the 5F3 level, while the lower-lying 5F5 level is populated due to direct radiative transitions 5F3, 2 → 5F5, obviating the cascade scheme 5F3 → (5F4, 5S2) ↝ 5F5. We conclude that NYF:Ho3+ crystals are processable; admit doping by holmium in high concentrations (up to 100%); and, with respect to all their radiative characteristics, can be considered as potential active media for solid-state continuously tunable lasers in the IR and visible ranges.

Spectroscopic study of erbium-activated crystals of double calcium yttrium fluoride Ca0.89Y0.11F2.11:Er3+: I. Intensity of spectra and luminescence kinetics

Ca0.89Y0.11F2.11:Er3+ (CYF:Er) crystals with an erbium content of 1–15 at % have been grown. The optical spectra and luminescence kinetics of CYF:Er crystals have been investigated at low (∼5 K) and room temperatures. Based on an analysis of the absorption spectra at low temperature, the structure of Stark splitting of erbium levels in CYF:Er crystals is determined. Room-temperature absorption spectra are used to calculate the spectra of absorption cross sections and oscillator strengths of transitions from the erbium ground state to excited multiplets. It is shown that the absorption spectrum of CYF:Er crystals contains broad bands in the ranges of 790–815 and 965–980 nm, which correspond to the range of emission of laser diodes. For the band peaking near 967 nm, the peak absorption cross section is σabsmax = 2.7 × 10−21 cm2. The intensity parameters are determined by the Judd-Ofelt method to be Ω2 = 1.39 × 10−20, Ω4 = 1.34 × 10−20, and Ω6 = 2.24 × 10−20 cm2. The radiative transition probabilities, radiative lifetimes, and branching ratios are calculated with these values. The luminescence decay kinetics from excited erbium levels upon selective excitation is investigated and the experimental lifetimes of the 4F9/2, 4S3/2, and 4G11/2 radiative erbium levels are determined. The dependences of multiphonon relaxation rates on the energy gap in CYF:Er crystals are obtained. The rates of nonradiative multiphonon relaxation from radiative erbium levels are determined.

Spectroscopic Study of Neodymium-Doped Sodium–Yttrium Double Fluoride Nd3+:Na0.4Y0.6F2.2 crystals

Nd3+:Na0.4Y0.6F2.2 (Nd3+:NYF) crystals are grown by the Stockbarger–Bridgman method for a stoichiometric mixture prepared by the solid-phase method and containing neodymium up to 20 at. %. The absorption spectrum of Nd3+:NYF crystals exhibits bands located in the emission region of laser diodes. The peak absorption cross section of the 796.8-nm band is σa = 0.96 × 10–20 cm2 and the bandwidth is Δλ = 17.5 nm. The most intense luminescence band is located at 1.05 μ m and the radiative time of the 4F3/2 level is τ0 = τexp ~ 960 μ s. It is shown that the 2P3/2 and 4D3/2 levels of Nd3+:NYF crystals are also radiative with lifetimes τ exp equal to ~110 and 9.5 μ s, respectively. However, these radiative transitions are partially quenched due to nonradiative relaxation. The intensity parameters Ω t are determined by the Judd–Ofelt method to be Ω2 = 1.18 × 10–20, Ω4 = 1.55 × 10–20, and Ω 6 = 2.85 × 10–20 cm 2. Using these parameters, the probabilities of radiative transitions and branching ratios are calculated, and the probabilities of nonradiative transitions are estimated. A conclusion is made that Nd3+:NYF crystals are promising as active media for diode-pumped tunable lasers, in particular, up-conversion-pumped lasers.

New materials for UV, VIS and mid-IR solid state lasers based on the rare earth doped double chloride crystals (TR/sup 3+/:KPb/sub 2/Cl/sub 5/)

Laser action of the TR:KPC (KPb/sub 2/Cl/sub 5/) crystals was achieved with Dy at 2.4 /spl mu/m. In the present work we continued studying this new systems based on TR/sup 3+/ doped chloride matrix suitable for diode-pumped lasers. We studied the optical spectra and luminescence kinetics, calculated radiative and nonradiative transition probabilities, considered up-conversion processes and possibility of energy transfer from exciton matrix band to TR/sup 3+/ ions. Intensive absorption band in UV spectral range (/spl lambda/<340 nm) associated with excitonic absorption formed by 6s/spl rarr/6p transitions in Pb/sup 2+/ ion. TR/sup 3+/ doped KPC crystals exhibit strong absorption bands in UV and IR.

Spectroscopic study of Na/sub 0.4/Y/sub 0.6/F/sub 22/:Nd/sup 3+/ crystals

Summary from only given. Compact upconversion pumped solid state lasers are one of the most active areas of laser research and development today. The efficiency of upconversion mechanisms was successfully demonstrated on a number of rare earth doped crystals with metastable levels including Nd-doped laser crystals.