Ni2+ emission in MgO,KMgF3, KZnF3 and MgF2

The emission of Ni²⁺ ions in MgO, KMgF₃, KZnF₃ and MgF₂ crystals has been investigated. The fine structure on the bands at about 20 000 cm^-1 and 13 000 cm^-1 has been studied in detail and from this and the excitation spectra these bands are assigned to ${}^1\text{T}{}_{\mathrm{2g}}\text{→}{}^3\text{A}{}_{\mathrm{2g}}$ and ${}^1\text{T}{}_{\mathrm{2g}}\text{→}{}^3\text{T}{}_{\mathrm{2g}}$ transitions respectively.     

Ni2+:BeAl2O4晶体发光性质的研究

用时间分辨的激光诱导荧光光谱方法测量了10—300K温度范围内Ni²⁺:BeAl₂O₄晶体的红外荧光光谱和荧光寿命。通过荧光寿命的温度变化特性分析,得出³T_2g态的内禀辐射衰减寿命为123±7.2μs。无辐射弛豫的Mott激活能为1147cm^-1,并导出了此晶体发光量子效率随温度的变化关系式。Ni²⁺:BeAl₂O_{4关键词：}     

Fluorescence of Mn2+ in CaCO3

The fluorescence of Mn²⁺ ion as impurity in CaCO₃ has been investigated. Emission bands from the ⁴D(E_g), ⁴D(T_2g) and ⁴G(T_1g) levels have been observed. The analysis of excitation and emission spectra has allowed to obtain the values of field strength (Dq) for the excited energy levels of Mn²⁺ in CaCO₃ lattice. The temperature dependence of excitation and emission spectra yield an activation energy for thermal quenching of luminescence very close to theoretical calculation. The behaviour of luminescence lifetime with temperature has also been obtained.     

Electronic pair excitations of Mn2+ and Ni2+ in perovskite fluorides: involvement of the 3 T 1g a state of Ni2+

Crystals of KZnF₃ and KMgF₃ doped with Mn²⁺ and Ni²⁺ were used to study the spectroscopic properties of Mn²⁺-F^--Ni²⁺ pairs. Pair transitions to the doubly excited states ⁴ E_g ^a , ⁴ A _1g (Mn)³ T _1g ^a (Ni) and ⁴ E_g ^b (Mn)³ T _1g ^a (Ni) were observed. The participation of the spin-allowed ³ A _2g →³ T _1g ^a excitation on Ni²⁺ in the pair transition is explained by spin-orbit mixing between ³ T _1g ^a and ¹ E_g . The prominent electronic origins are assigned to the double spin-flip transitions ⁶ A _1g (Mn)³ A _2g (Ni) →⁴ E_gu(Mn)³ T _1g ^a (Γ₃)v(Ni) and ⁴ A _1g (Mn)³ T _1g ^a (Γ₃)v(Ni). The former lie at lower energy and are more intense than the corresponding ⁶ A _1g (Mn)³ A _2g (Ni) →⁴ E_gv(Mn)³ T _1g ^a (Γ₃)u(Ni) transitions involving two orbital jumps. The well-resolved vibronic structure is composed of three basic vibrations of ～ 150 cm^-1, ～ 294 cm^-1 and ～ 508 cm^-1 in the KZnF₃ host.     

Excited-state absorption of Co2+ in MgF2 and KZnF3

We report on measurements of excited-state absorption spectra and absolute cross-sections in Co²⁺-doped KZnF₃ and MgF₂ at room temperature in the near-infrared domain. The data are compared with the predictions of the single-configuration co-ordinate model.     

Broadband infrared luminescence from transparent glass–ceramics containing Ni<Superscript>2+</Superscript>-doped <Emphasis Type="BoldItalic">β</Emphasis> -Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocrystals

Transparent Ni²⁺-doped β-Ga₂O₃ glass–ceramics were synthesized. The nanocrystal phase in the glass–ceramics was identified to be β-Ga₂O₃ and its size was about 3.6 nm. It was confirmed from the absorption spectra that the ligand environment of Ni²⁺ ions changed from the trigonal bi-pyramid fivefold sites in the as-cast glass to the octahedral sites in the glass–ceramics. The broadband infrared emission centering at 1270 nm with full width at half maximum (FWHM) of more than 250 nm was observed. The fluorescence lifetime was about 1.1 μs at room temperature. The observed infrared emission could be attributed to the ³ T _2g (³ F )→³ A _2g (³ F ) transition of octahedral Ni²⁺ ions. It is suggested that the Ni²⁺-doped transparent β-Ga₂O₃ glass–ceramics with broad bandwidth and long lifetime have a potential as a broadband amplification medium. PACS 42.70.-a; 42.70.Ce; 81.40.Tv     

Optical spectra of nearest neighbour nickel pairs in KMgF3 and KZnF3 crystals

The absorption, MCD, and emission spectra associated with the nearest neighbour Ni²⁺ pairs in KMgF₃ and KZnF₃ have been studied and analysed on the basis of the theory which includes spin dependent excitation transfer as well as spin independent transfer. It is shown that excitation transfers are important in determining the pair energy levels for the case where the singleion states involve orbital degeneracy. The antiferromagnetic J value of the ground state is determined to be 68 cm^-1.     

Excited-state absorption of Co2+ in MgF2 and KZnF3

We report on measurements of excited-state absorption spectra and absolute cross-sections in Co²⁺-doped KZnF₃ and MgF₂ at room temperature in the near-infrared domain. The data are compared with the predictions of the single-configuration co-ordinate model.     

Spectroscopic properties of alexandrite crystals II

Several aspects of the optical spectroscopic properties of alexandrite crystals not previously investigated are reported here. For Cr³⁺ ions occupying the Al³⁺ lattice sites with mirror symmetry in BeAl₂O₄, the positions of the zero-phonon lines for absorption transitions to the ²T_1g and ⁴T_2g levels are identified, and vibronic transition peaks in the fluorescence spectrum are compared to transitions appearing in the Raman spectrum and Stokes excitation spectrum. In addition, the effects of radiation trapping are shown to lengthen the fluorescence lifetime of the ²E_g - ⁴A_2g transition for ions in these sites at low temperatures. For Cr³⁺ ions occupying the Al³⁺ lattice with inversion symmetry, the ground state splitting of the ²E_g - ⁴A_2g transition is reported and the decrease of the fluorescence lifetime with temperature is shown to be due to the increase in vibronic emission probability as well as increased probability of direct radiationless decay.     

Excitation spectra and fluorescent lifetime measurements of Mn2+ in CaF2 and CdF2

The excitation spectrum of the Mn²⁺ emission has been measured in CaF₂ and CdF₂. The observed excitation bands have been assigned to transitions of the Mn²⁺ ions in a cubic environment. The calculated values for the crystal field (Dq) and Racah parameters (B,C) are Dq = 425 cm^-1 for CaF₂, Dq = 500 cm^-1 for CdF₂ and, B = 770 cm^-1 and C / B = 4.48 for both compounds. The lifetime of the fluorescent level ⁴T_1g(⁴G) has been measured in both compounds at different temperatures in the range from 10 to 500 K. The lifetime thermal dependence is explained taking into account different mechanisms (purely radiative, phonon assisted, and radiationless transitions) for the decay of excited Mn²⁺ ions.     

Crystal-field hamiltonian and spin-orbit interaction for d and d ions at low C3 symmetry sites: V:Al2O3 and Ni:LiNbO3

The experimental studies have provided evidence of the occurrence of transitions from the ³T_1g(³F) ground state to the crystal-field levels ³T_2g(³F), ³T_1g(³P) and ³A_2g(³F) for the V³⁺ centres in Al₂O₃ crystal; and from the ³A_2g(³F) ground state to the crystal-field levels ³T_2g(³F), ³T_1g(³F) and ³T_1g(³P) for the Ni²⁺ centres in LiNbO₃ crystal (levels are assigned to irreps of the O_h point symmetry group). Using the experimental spectroscopic data, theoretical calculations of the crystal-field levels of V³⁺:Al₂O₃ and Ni²⁺:LiNbO₃ are carried out based on the Racah theory. The observed crystalline-field splittings of the V³⁺ and Ni²⁺ terms were accounted for using a C₃ symmetry Hamiltonian. The spin-orbit interaction was taken into account in this work. The Racah, crystal-field and spin-orbit parameters, which fit experimental and theoretical energy levels, have been reliably obtained. A good agreement between the theoretical and experimental results for the energy levels of V³⁺:Al₂O₃ and Ni²⁺:LiNbO₃ has been obtained.     

CW infrared laseraction of optically pumped Co2+:KZnF3

The optical properties of KZnF₃:Co²⁺ were investigated by means of absorption and emission spectroscopy in the visible and infrared spectral region. This system is suitable for laseraction between the lowest ⁴T₁(⁴F)-⁴T₂(⁴F) Co²⁺ phonon sidebands. CW laseraction of more than 20 mW (85K) was observed at 1.95 μm when pumped with an Ar⁺-laser at 514 μm (1.5W). The system is at least tunable between 2.05 μm to 1.85 μm.     

X-ray stimulated luminescence in MgO

Studies have been made of the emission spectrum of MgO crystals induced by X-irradiation at 90 K. Two bands (half-widths ～0.8 eV) were observed to peak at 4.95 and 3.2 eV, respectively, in high purity crystals. Doping with 100 ppm or greater of Fe, Co, Cr, Cu, Mn, and Ni suppressed the luminescence, though in the MgO:Ni crystal the 2.3 eV Ni²⁺ band due to the ¹T_2g→³A_2g transition was observed. In deuterium-doped crystals the ratio of the intensity of 3.2–4.95 eV emission was found to be 1.2 as compared to 8 for the undoped crystals. Prior exposure of the pure crystals to ionizing radiation enhances the 4.95 eV band by a factor of three while not affecting the 3.2 eV band. This enhancement of intensity decays in several stages upon standing at room temperature in a way that reflects the thermal stability of the various components of the composite V-band absorption. These facts together with the observation that the 210 K thermoluminescence peak is composed entirely of 4.95 eV emission indicate that this luminescence band is associated with the recombination of an electron with a hole located in a V-type center, i.e. O?□ + e → (O²?□)1 → O²?□ + 4.95 eV, where the square indicates that the perturbing positive ion vacancy is adjacent to the oxugen ion which has captured the hole. In MgO:Li⁺, which exhibits no V-type centers upon irradiation, the 4.95 eV band was absent and a 2.9 eV emission which may be associated with recombination at the [Li]⁰ center was observe.     

Absorption and emission spectra of yttria-stabilized zirconia and magnesium oxide

We have investigated the luminescence and absorption spectra of doped and undoped ZrO₂-Y₂O₃ and MgO crystals at room- and low temperatures. The crystals used are partly doped with the transition metals Ni, Co, Cr and the rare earth Pr. The emission spectra were obtained under laser excitation at different wavelengths. The observed optical emission and absorption bands of the MgO crystals doped with Ni, Co and Cr correspond to transitions between spin-orbit split crystal field levels of the transition metals. Luminescence and absorption bands of undoped yttria-stabilized zirconia (YSZ) crystals are due to color centers, absorption bands of the doped YSZ correspond to the well known transitions of the Ni²⁺, Co²⁺ and Pr³⁺ ions, respectively. The emission spectra of the doped YSZ obtained under various laser excitations can be explained by an energy transfer process between the color center and the doping materials. The influence of annealing on the absorption and emission of Pr³⁺/Pr⁴⁺ is investigated.     

Ni2+ doped LaMgAl11O19: A potential vibronic laser system near 1.1 μm

We report here the optical absorption and fluorescence characteristics of the Ni²⁺ ions in lanthanum hexa-aluminate LaMgAl₁₁O₁₉. It shows the existence of a broad-band emission extending from 0.95 up to 1.4 μm associated with the lower energy downward vibronic transition ³T₂(³F) → ³A₂(³F) of Ni²⁺ ions in quasi-octahedral symmetry sites. The lifetime of t his infrared emission has been measured at different temperatures from 14 up to 600 K and as a function of Ni²⁺ ion concentration. The results indicate that LaMgAl₁₁O₁₉:Ni²⁺ could be a solid-state laser material of great interest, since it would work at room temperature in a large spectral domain, provided that one uses pumping wavelengths which correspond to regions of minimal absorption by tetrahedrally coordinated Ni²⁺ ions, and also if one favours the relative occupancy of the Ni²⁺ ions in the octahedral sites by appropriate chemical treatments.     

Er3+/Yb3+共掺碲硼硅酸盐玻璃的光谱性质和热稳定性研究

制备了系列Er³⁺/Yb³⁺共掺碲硼硅酸盐玻璃样品(85-x)TeO₂-15B₂O₃-xSiO₂ (TBS x=0,5,10,15,20 mol%).测试和分析了样品的吸收光谱、荧光光谱、能级寿命、红外透射光谱及差热特性.并通过对Er³⁺离子⁴I_13/2→⁴I_15/2跃迁发射谱线的高斯拟合，设计了一个简单的四能级结构估算了Er³⁺离子⁴I_13/2和⁴I_15/2能级在碲硼硅酸盐中的Stark分裂情况.研究表明SiO₂的引入能有效地改善玻璃的热稳定性和光谱性能，玻璃析晶温度T_x与玻璃转变温度T_g之差(ΔT=T_x-T_g)可达178℃，说明碲硼硅酸盐是一种适合于光纤拉制的玻璃基质材料.比较了不同基质玻璃中Er³⁺离子的荧光半高宽和受激发射截面，结果表明TBS玻璃系统具有较好的带宽性能，是一种优良的宽带光纤放大器候选基质材料. 关键词： 碲硼硅酸盐 热稳定性 高斯拟合 -基')" href="#">OH^-基     

Electron-vibration splitting of the vibronic levels of the 1T2g state of MgO:Ni2+

Magnetic circular dichroism (MCD) and magnetic linear dichroism (MLD) measurements of the ${}^3\text{A}{}_{\mathrm{2g}}\text{→}{}^1\text{T}{}_{\mathrm{2g}}$ absorption band in MgO:Ni²⁺ are reported. It is shown that for the lowest energy vibrational peak there is considerable evidence of splitting of the T_2g × T_1u vibronic levels by the electron-vibration interaction.     

High resolution MCD spectroscopy of transition metal ions in fluoride crystals

Measurements of the MCD spectra of Ni²⁺ in KMgF₃ and KZnF₃ have confirmed and extended previous assignments of spin-orbit structure based on similarities of vibrational patterns. The measurements also reveal the presence of a ¹ A _1g (¹ G) state which interacts strongly with the ³ T _1g ^b (³ P) state. The MCD spectra of the tetragonal crystals K₃Ni₂F₇ and K₂NiF₄ have been measured for the transitions ³ A _2g →³ T _1g ^a , ¹ E_g . The spectrum of K₃Ni₂F₇ is characterized by the appearance of electric dipole zero phonon lines, consistent with the C _4v site symmetry of the Ni²⁺ in the paramagnetic phase. An analysis of the MCD spectrum allows a positive assignment of six of the seven states (from ³ T _1g ^a and ¹ E_g ) to which transitions are allowed by symmetry in the axial spectrum. A complete tetragonal crystal-field analysis has been made which shows that the distortion is an axial compression of the fluoride octahedron. The absorption spectrum of K₂NiF₄ shows much less vibrational structure, but the MCD spectrum allows a definitive assignment of six states (from ³ T _1g ^a and ¹ E_g ) through a _2u vibrations in the usual vibronic mechanism. False origins based on e_u phonons have not been identified. The tetragonal field is larger than for K₃Ni₂F₇ and corresponds to an axial compression, in agreement with the known crystal structure.     

Indirect measurements of the Jahn-Teller quenched spin-orbit splitting in the 5T2g-state of KMgF3:Fe2+

The energy separation of the first excited spin-orbit States Γ_3g, Γ_4g from the Γ_5g ground state, in the orbital ⁵T_2g triplet state of Fe²⁺ in KMgF₃, has been estimated from temperature dependence measurements on the 7860 cm^-1 zero-phonon-line (ZPL) transition from Γ_5g to the orbital ⁵E_g doublet state. Using a simplified crystal field energy level model, we find the Γ_5g Γ_3g, Γ_4g separation to be ～30 cm^-1, indicating that the vibronic Jahn-Teller coupling is considerably stronger in KMgF₃:Fe²⁺ than in MgO:Fe²⁺. Far infrared absorption data on KMgF₃:Fe²⁺ in magnetic fields up to 6T, are found to be consistent with this interpretation.     

UV-violet emission properties of 2F(2)5/2 energy level of Nd3+ ions in ZBLAN glass

In this work the short-wavelength emission properties are investigated for the highest observed 4f metastable energy level ²F(2)_5/2 of Nd³⁺ ions in fluorozirconate ZBLAN glass. Various dopant concentrations, ambient temperatures and excitation conditions have been considered throughout the study. Distinct spectral features were observed under pulsed and cw excitation at 514 nm. In particular, pulsed pumping enabled recording of ²F(2)_5/2 emission spectra, not observable under CW excitation, as well as the level’s fluorescence decay dynamics and its evolution with temperature and dopant concentration. According to the best of the authors’ knowledge, neither the fluorescence lifetime of ²F(2)_5/2 of Nd³⁺ in ZBLAN, nor its concentration dependent evolution were reported before.