M. J. Weber

Luminescence of Bi4 Ge3 O12 : Spectral and decay properties

Intense broadband emission in the visible is observed from crystals of Bi4Ge3O12 under optical and x‐ray excitation. From measurements of absorption, reflection, fluorescence, and excitation spectra, the emission is assigned to 3P1 → 1S0 transitions of Bi3+. The Stokes shift is large, [inverted lazy s]14 000 cm−1. The temperature dependences of the fluorescence intensity and lifetime in the range 77–400 °K establish that nonradiative decay becomes significant at temperatures ⪞250°K. Comparison of the properties of Bi4Ge3O12 with those of Bi12GeO20 and other bismuth‐activated materials demonstrates the importance of the Stokes shift and the 1S‐3P energy difference in determining the luminescence behavior. The use of Bi4Ge3O12 as a laser host crystal for rare‐earth and iron group activator ions, and as a scintillator material is discussed briefly.

Optical spectra of Ce3+ and Ce3+‐sensitized fluorescence in YAlO3

Infrared and ultraviolet absorption spectra arising from f→f and f→d transitions of Ce3+ in YAlO3 crystals are presented and used to derive the 4f and 5d energy levels. Excitation and fluorescence spectra of 5d→4f emission are also reported. The 5d fluorescence has a decay time of 16 nsec and a radiative quantum efficiency of near unity at 300 °K. Possible use of Ce3+ as a sensitizer for rare‐earth and iron‐group ion fluorescence in YAlO3 is surveyed; included is an investigation of energy transfer in a Ce, Nd, Cr‐codoped crystal.

Optical Spectra and Intensities of Nd3+ in YAlO3

The optical absorption and emission spectra, fluorescence kinetics, and radiative and nonradiative transition probabilities of Nd3+ ions in YAlO3 are investigated. Measurements are presented of the energy levels, absorption and emission cross sections, linewidths as a function of temperature and Nd concentration, thermal line shifts, and fluorescence branching ratios. Judd‐Ofelt intensity parameters for electric‐dipole transition probabilities are derived from measurements of the absorption spectrum. Stimulated emission cross sections, absorption‐band intensities, fluorescence quantum efficiency, possible excited‐state absorption, and other properties of importance for YAlO3:Nd3+ laser action are discussed.

Chromium Ion Pair Interactions in the Paramagnetic Resonance Spectrum of Ruby

The paramagnetic resonance spectrum of Cr3+ pairs in ruby which interact via exchange and dipolar forces have been studied at 15.74 kMc in the temperature range 1.2° to 700°K. Theoretical analysis predicts and experiments confirm that relatively distant neighbors with negligible exchange coupling give rise to resonance lines which cluster around isolated Cr3+ ion lines. Spin pairs coupled through exchange forces large as compared to the Zeeman or crystalline field energies give rise to lines that cluster around magnetic field values different from those for isolated Cr3+ lines. Exact calculations on an IBM 704 computer are used to assign lines in a given cluster to various neighbor pairs. This assignment together with the temperature dependence of the line intensities are used to determine the exchange forces. For nearest neighbors the exchange constant is 390±50 cm−1 while the 3rd through 11th neighbor shells have exchange interactions of order 1 cm−1. Spin-lattice relaxation is discussed for pairs coupl...

Laser Action and Spectroscopic Properties of Er3+ in YAlO3

Stimulated emission at 1.663 μ due to a 4S3/2→4I9/2 transition has been observed from Er3+ ions in a crystal of YAlO3. The threshold for pulsed laser action at room temperature was 52 J. Crystalline Stark levels determined from absorption and fluorescence spectra and fluorescence lifetimes of YAlO3:Er3+ are reported.

Chromium—rare‐earth energy transfer in YAlO3

Energy transfer between chromium and rare‐earth ions in YAlO3 was investigated from fluorescence excitation spectra and fluorescence decay studies. Rare earths examined include Nd3+, Ho3+, Er3+, Tm3+, and Yb3+. Chromium—to—rare‐earth transfer was observed in all cases; evidence of rare‐earth—to—chromium transfer was also observed for Ho3+. Phonon‐assisted transfer rates are dependent on the energy mismatch of the transitions for the two ions involved. The efficiency of the Cr3+ → Nd3+ energy transfer in YAlO3 was measured at 300°K and found to be greater than in Y3Al5O12 for comparable dopant concentrations. Use of chromium as a sensitizer for rare‐earth fluorescence and laser action is discussed.

Optical spectra and relaxation of Cr3+ ions in YAlO3

Optical absorption and emission spectra of Cr3+ ions in YAlO3 have been investigated at 300 and 77°K. In the cubic field approximation, the spectra can be fitted by the parameters Dq = 1800 cm−1, B = 590 cm−1, C = 2980 cm−1. An intense vibronic spectrum is associated with 2E → 4A2 fluorescence transitions. Measurements of absorption cross sections and oscillator strengths, thermal broadening and shifts of the R‐line fluorescence, and lifetimes of the 2E fluorescence and Cr3+‐Cr3+ pair lines are reported. At low temperatures and chromium concentrations, the radiative quantum efficiency of the 2E state is approximately unity. Other relaxation processes become important at temperatures > 400°K. The possibility of observing stimulated emission from YAlO3:Cr3+ is discussed.

Energy Transfer and Fluorescence Quenching in Eu‐ and Nd‐Doped Silicate Glasses

Radiative and nonradiative energy transfer and decay processes have been investigated in high silicate glasses co‐doped with Eu and Nd. Energy transfer from Eu to Nd was established from an examination of the excitation spectra and the increased Eu decay rates in the presence of Nd. Measurements of the concentration dependences of the Eu3+ and Nd3+ fluorescence lifetimes reveal the presence of four distinct processes arising from various ion‐ion interactions: (1) self‐quenching of the Nd3+ fluorescence, (2) self‐quenching of the Eu3+ fluorescence, (3) nonradiative energy transfer from Eu3+ to Nd3+, and (4) Eu quenching of the Nd3+ fluorescence. This last process decreases the radiative quantum efficiency of the 4F3/2 state of Nd3+, thus limiting the attractiveness of Eu sensitization for Nd laser action.

Chromium‐ytterbium energy transfer in silicate glass

Energy transfer has been observed between trivalent chromium and ytterbium ions in a silicate glass. Optical absorption and emission spectra of Cr3+ and Yb3+ are presented and show that the chromium emission, which occurs as a broad‐band fluorescence in the near‐infrared, overlaps the ytterbium absorption. Hence Cr3+ ions can be used to sensitize YB3+ fluorescence. Cr3+‐to‐Yb3+ energy transfer was established from the Yb3+ fluorescence excitation spectrum and the decrease in the Cr3+ fluorescence intensity and lifetime. A decrease in the Yb3+ lifetime with increasing Cr3+ content was also observed indicating relaxation of Yb3+ by back transfer to the faster relaxing Cr3+ ions. Measurements of the Yb3+ and Cr3+ fluorescence lifetimes as a function of temperature and chromium content are reported.