Search

Judd–Ofelt (J–O) theory has been applied to a series of LiLa 1− x Eu x (PO 3 ) 4 ( x = 5%; 10%; 15%; 20% and 30%) polycrystalline powders based on their emission spectra. J–O intensity parameters Ω λ ( λ = 2, 4) and various radiative properties such as the radiative transition probability ( A ), radiative life time ( τ R ), branching ratio ( β R ) and stimulated emission cross-section ( σ e ) have been determined. The observed trend for J–O parameters ( Ω 2 < Ω 4 ) reveals the ionic character of La(Eu)–O bond as well as the symmetry environment around the Eu 3+ ion in LiLa(PO 3 ) 4 . The experimental decay curves of the 5 D 0 level in LiLa 1− x Eu x (PO 3 ) 4 have a single exponential profile. The registered long life time, low multiphonon relaxation rates ( W NR ), high quantum efficiency ( η ) and the best optical gain parameter ( σ e x τ exp ) have been discussed as function of Eu 3+ concentration, chemical composition and crystal structure of the host matrix and particle-size distribution. A comparative study reveals that LiLa 1− x Eu x (PO 3 ) 4 is promising for use in optical devices as well as for developing visible red lasers to emit at 613 nm. The optical band gap energies of LiLa 1− x Eu x (PO 3 ) 4 have been calculated from the diffuse reflection spectral measurements. The results were discussed as a function of Eu 3+ concentration and compared to reported theoretical results. [ABSTRACT FROM AUTHOR]

Highlights: [•] The fluorescence properties of 2.7μm emission and energy transfer mechanism are investigated. [•] The optimized concentration ratio of Er3+ to Ho3+ is found to be 1:1. [•] The sample possesses large emission cross section and radiative transition probability. [•] The energy transfer microparameters are calculated and discussed. [ABSTRACT FROM AUTHOR]

Abstract: The work is aimed to research of CsI:Eu single crystals’ luminescence at different excitations in the wide temperature range (from 8 to 300K) and admixture concentration from 10−4% up to 10−1% of Eu2+ ions. This study was directed to separation of different luminescence mechanisms and luminescence quenching explore. It is found that due to the temperature quenching the room temperature yield is decreased in order of magnitude even for heavy Eu doped CsI crystals. Intense low temperature luminescence band at 441–448nm connected with Eu2+ 4f 6 5d →4f 7 radiative transition is observed. The results obtained show that the excitonic mechanism plays the main role in energy transfer process to Eu2+ ions and this is the reason for relatively low light yield of this emission at RT. The nature of the additional emission bands (410, 450, 480 and 500nm) are apparently caused by the significant non-isomorphism of cations and/or by the presence of oxygen-containing admixtures. [Copyright &y& Elsevier]

Abstract: The photoluminescence and excitation spectra of Pr3+ activated LaPO4 has been investigated in the 1.6–300K temperature region. At room temperature, the luminescence of LaPO4:Pr3+ is composed of the interconfigurational 4f15d1 →4f2 emission transitions. However, in the 1.6–60K temperature range, the emission spectrum also consists of the intraconfigurational emission transitions that emanate from the 1S0 state. A radiative lifetime of 145ns is measured for the Pr3+ 1S0 → 1I6 emission transition in LaPO4. This is one of the shortest radiative lifetime observed for this transition in a solid. The energy position of the Pr3+ 1S0 state in LaPO4 is established by high-resolution emission spectrum at 46 375±5cm−1. A detailed analysis of the thermal quenching of the 1S0 lifetime and emission intensity is presented. It is proposed that the lowest energy state of the relaxed 4f15d1 configuration is situated energetically below that of the 1S0 state. [ABSTRACT FROM AUTHOR]

Abstract: Here we present the results of our theoretical study of the optical characteristics (lifetimes, IR absorption coefficient, Raman gain coefficient) for small-radius optical centers in subwavelength spherical and ellipsoidal nanocrystals embedded in a dielectric medium. [ABSTRACT FROM AUTHOR]

Abstract: The temperature dependence of the spectral positions and widths of the photoluminescence lines corresponding to the 5D0 → 7F0, 5D0 → 7F1 and 5D1 → 7F0 electronic transitions in Sm2+-doped SrFCl crystal was measured between 87 and 625K at ambient pressure. The temperature dependence of the homogeneous line width Γh (T) for all these transitions in the whole temperature range used can be described by the two-phonon Raman scattering of acoustic phonons with the Debye temperature TD ≈230K. Comparison of the temperature- and pressure-induced shifts revealed why all the emission lines studied show the blue temperature shifts. It is so because a greater part of the line shift is caused by the thermal expansion of the host crystal and not by enhancement of the electron–phonon coupling with increasing temperature. [ABSTRACT FROM AUTHOR]

Abstract: Spectroscopic characterization for optical amplification and laser application of the Er3+-doped Bi4Si3O12 glass is performed through its absorption and luminescence spectra. The spontaneous radiative transition probabilities from the first seven excited states to the ending states are calculated to obtain the luminescence branching ratios and radiative lifetimes. Intense infrared to visible luminescence of the Er3+ ion is observed with 4I9/2 state excitation (800nm) under a 200mW laser excitation power. The value obtained for the ratio of the 4I11/2 → 4F7/2 excited-state absorption oscillator strength to the 4I15/2 → 4I11/2 ground state absorption oscillator strength is in accordance with those reported for Er3+-doped materials pumped efficiently at 4I11/2 level excitation wavelengths. Gain cross-section spectra as a function of the inverted population rate and the stimulated emission cross-section spectrum were determined for the 4I13/2 → 4I15/2 infrared (IR) laser transition. The large gain bandwidth of the 4I13/2 → 4I15/2 IR emission has resulted in being close to those reported for Er3+-doped oxide glasses suitable for broadband amplifiers. [Copyright &y& Elsevier]

Abstract: Fluorophosphates glasses YF3–BaF2–Ba(PO3)2 doped with Er3+ and Er3+–Yb3+ were prepared and the structures of the samples were briefly investigated. The experimental intensity parameters were calculated according to the Judd–Ofelt theory, from which the radiative transition probabilities, fluorescence branching ratios, and radiative lifetimes of Er3+ were obtained. Bright green and red upconversion emissions was observed in Er3+–Yb3+ co-doped samples excited by 980nm laser diode, and two-photons absorption processes were determined for the emissions by examining the dependence of the emission intensity on the excitation power. The concentration effects on the intensity and decay time of the upconversion emission revealed that growing Er3+ concentration declined the probability of sequential energy transfer from Yb3+ to Er3+, and thus increasing the intensity ratio of the red emission to the green ones. The temperature effects on the intensity ratios of different emission bands showed that the maximum transducer sensitivity based on the fluorescence intensity ratio (FIR) was calculated to be 0.0015/°C at 6°C. [Copyright &y& Elsevier]

Abstract: Structural and spectroscopic properties of neodymium doped sodium borate and fluoroborate glasses of composition (in mol%) (99− X) B2O3 + XNa2O+1Nd2O3, X =49.5, 39.5 and 29.5 and 49.5B2O3 + XNa2O+(49.5− X) NaF+1Nd2O3, X =0 and 24.75 have been investigated using XRD, FTIR, absorption and emission spectra and decay curve. The XRD of the glasses confirm their glassy nature and the FTIR spectra reveal the presence of BO3 and BO4 units along with the strong OH− groups in the glasses. The UV–vis-NIR absorption spectra were used to calculate the bonding parameters ( and δ), to identify the ionic/covalent nature of the glasses. The spectral intensities have been calculated by using Judd–Ofelt analysis and inturn used to estimate radiative properties such as radiative transition probabilities, radiative lifetimes, branching ratios, peak stimulated emission cross-sections. Branching ratios and stimulated emission cross-sections show that the 4F3/2 → 4I11/2 transition of the glasses under investigation has the strong emission around 1060nm. The decay from the 4F3/2 level of Nd3+ ions is found to be single exponential. Multiphonon relaxation and quenching due to OH− groups play a governing role in the luminescence quenching of 4F3/2 level of Nd3+ ions in the titled glasses. The results obtained are compared with reports on similar glasses. [Copyright &y& Elsevier]

Abstract: 53.3BiO1.5–33.3GeO2–13.4NaO0.5 (cation%) glasses with various Tm3+ concentration were prepared by melt-quenching method. These glasses show high density, high refractive index, low phonon energy and good stability against crystallization. Absorption spectra of Tm3+-doped bismuthate glass were measured to obtain the radiative lifetimes by Judd-Ofelt theory. The absorption (4.5×10−21 cm2) and emission (6.7×10−21 cm2) cross-sections were calculated by Beer–Lambert and McCumber theory. The results show that the Tm3+ (3F4 → 3H6) in these glasses have high spontaneous radiative transition probabilities and large stimulated emission cross-section. Then the fluorescence emission spectra were measured under 808nm excitation and the maximum emission intensity at 1.8μm is obtained at 0.9mol% Tm2O3 in the glasses. [Copyright &y& Elsevier]

Abstract: Evidence of a positive optical gain has been observed in an Er3+-doped LuVO4 crystal in a pump and probe experiment. The radiative transition from the 4S3/2(2H11/2) level to the 4I13/2 metastable level of the Er3+ ion gives rise to an intense emission centred at 850nm. The 4S3/2(2H11/2) level of Er3+ ions is populated with high power laser pulses at 532nm due to the 4I15/2 → 4S3/2(2H11/2) ground state absorption. The 4S3/2(2H11/2)→ 4I13/2 electronic transition is stimulated with a low signal cw beam at 850nm. Under these conditions, the high power pump pulses allowed to reach the population inversion necessary between the Er3+ levels of the transition 4S3/2(2H11/2)→ 4I13/2. An increase of the emission intensity of the sample is observed at the signal wavelength, due to the stimulated emission. Positive optical gain around 2cm−1 (8.6dB/cm) has been measured in Er3+-doped LuVO4 crystal. [Copyright &y& Elsevier]

Abstract: From radiative transitions rates in praseodymium, neodymium, erbium, holmium and thulium ions doped LaAlO3 and measured emission decay times multiphonon nonradiative transitions rates W MNR have been calculated. Radiative transition rates were determined in the frame of Judd–Ofelt theory. The data obtained were plotted in the function of energy gap ΔE and fitted by exponential function W MNR =B·exp(−α ·ΔE), where B =1.02×109 and α =3.61×10−3. Fitting results show that multiphonon nonradiative transition rates are low comparing to other oxide crystals being similar to those of YAG. [Copyright &y& Elsevier]