Andranik G. Avanesov

Photon cascade emission in SrAlF5:Pr3+

The optical properties of SrAlF5:Pr3 + are studied. Emission measurements up to 1200 nm under blue-light excitation in the3P2 level reveal a large number of emissions all originating from the3P0 level and the1D2 level. Under vacuum ultraviolet excitation in the 4f15d1 bands, emission from the1S0 level, followed by emission from the3P0 level and the1D2 level takes place. This is known as the photon cascade emission process. The excitation spectrum of the1S0 emission was measured and was compared with the excitation spectrum of SrAlF5:Ce3 +. The spectrum for SrAlF5:Pr3 + compared to SrAlF5:Ce3 + is at about 12 240 cm−1 higher energy. A study of the x-ray-excited emission in the temperature region from 100 to 350 K was performed, determining the processes responsible for both1S0 and3P0/1D2 emissions.

The observation of photon cascade emission in Pr3+-doped compounds under X-ray excitation

Abstract The problem of obtaining two visible photons from a single incident vacuum ultraviolet photon is considered and conditions of cascade emission observation in various Pr 3+ -activated compounds are reviewed. Hosts with weak crystal field, low phonon energies, large band gap, large cation–anion distance, and large coordination number for the substitution site are desirable. Emission spectra and decay curves under X-ray excitation of some Pr 3+ -doped materials: LaAlO 3 , LaMgAl 11 O 19 , SrAl 12 O 19 and SrAlF 5 have been measured. Photon cascade emission has been observed in SrAl 12 O 19 :Pr 3+ and SrAlF 5 :Pr 3+ . The influence of the Pr 3+ concentration on the emission has been studied in SrAl 12 O 19 :Pr 3+ . Intrinsic (excitonic) luminescence, which has an adverse effect on the cascade emission, is usually suppressed in compounds containing 0.5 or more percent of Pr 3+ .

Laser performance of Cr2+-doped ZnS

Laser properties and spectroscopic characterization of diffusion doped Cr2+: ZnS crystals synthesized by chemical transport reaction from gas phase are reported. Lasing was realized with a threshold of 170 uJ and slope efficiency of 9.5 % with respect to the 1.5607 um pump energy, in a hemispherical cavity. Low doped samples (3-4 cm-1 at 1.7 um) of 1.7 mm thickness were utilized. The 1.5607 um excitation was realized with a D2 Raman cell pumped in a backscattering geometry by the 1.064 um radiation of the single frequency Nd:YAG laser. Maximum output energy reached 100 uJ. Lasing in the hemispherical cavity was achieved with output couplers R=80 % and 90 % at 2.36 um and radius of curvature 20 cm. Absorption cross section was estimated from spectroscopic measurements and was in a good agreement with saturation data (0.80x10-18 cm2) calculated with the modified Frantz-Nodvik equation for a four level slow absorber. Findlay Clay losses were found to be about 14%. Selective cavity experiments were performed in a hemispherical cavity with a CaF2 prism as the dispersive element. A tuning range of 2.05-2.40 um was realized, limited by the spectral range of the output coupler of the selective laser cavity.

Spectroscopic characterization and laser performance of diffusion doped Cr2+:ZnS

Spectroscopic, saturation, and laser properties of diffusion doped Cr2+:ZnS crystals synthesized by chemical reaction from gas phase are reported. Lasing was realized with a threshold of 170 µJ and slope efficiency of 9.5% with respect to the 1.5607 µm pump energy, in a hemispherical cavity. Maximum output energy reached 100 µJ. A tuning range of 2.05-2.40 µm was realized, limited by the spectral range of the output coupler of the selective hemispherical laser cavity. Selective cavity experiments used a CaF2 prism as the dispersive element. Findlay Clay losses were found to be about 14%. Absorption cross section (0.80×l0−18 cm2) was estimated from spectroscopic measurements and was in good agreement with saturation data, calculated with the modified Frantz-Nodvik equation for a four level slow absorber.

High-frequency EPR of Cr2+ ions in CdGa2S4

High-frequency broad-band (65–240 GHz) EPR is used to study impurity centers of bivalent chromium in a CdGa2S4 crystal. It is found that the EPR spectra correspond to tetragonal symmetry. The spin Hamiltonian H = βB · g · S + B20O20 + B40O40 + B44O44 with the parameters B20=23659±2 MHz, B40=1.9±1 MHz, |B44|=54.2±2 MHz, g‖=1.93±0.02, and g⊥=1.99±0.02 is used to describe the observed spectra. It is concluded that chromium ions occupy one of the tetrahedrally coordinated cation positions.

High-frequency tunable EPR spectroscopy of non-Kramers ions in AgGaSe2: Cr, AgGaS2: Cr, and CdGa2S4: Cr crystals

Crystals of the chalcopyrite family, AgGaSe2, AgGaS2, and CdGa2S4, doped with chromium ions have been investigated using high-frequency broad-band EPR spectroscopy in the range 65–530 GHz at T = 4.2 K. It has been revealed that, in the AgGaSe2 and AgGaS2 crystals, the Cr2+ ions occupy positions with orthorhombic and tetragonal symmetry, whereas the previously investigated CdGaS4 crystals contain only tetragonal centers. The observed spectra have been described in the framework of the spin-Hamiltonian formalism. Apart from the divalent chromium centers, the EPR lines attributed to non-Kramers ions are observed in the frequency range 300–450 GHz for all the crystals under investigation. The nature of these lines has been discussed.

Interconfiguration and intraconfiguration transitions of Pr3- in some oxides and flourides

There is a very great interest to obtain luminophors with a large quantum efficiency. One way to realize this is the employment of photon cascade emission. We present result of a search for new materials with cascade emission in Pr3+ intraconfiguration f-f transitions. The influence of host lattices, temperature, Pr concentration of f-f and d-f transitions has been studied.

Oscillating field model in the theory of optical spectra

Usually, broad-band spectra of transition-metal ions are explained as a result of vibrational quantas emission or absorption. In this paper optical spectra are interpreted as a result of oscillator position detecting by absorption or emission of light quantum. The basis of coherent oscillator states is then used in averaging procedure to obtain spectrum lineshape. Such formalism is useful in high-temperature limit and excitation by ultrashort laser pulses. Parameters of effective dipole momentum to calculate optical transition strength for any configuration of crystal lattice are introduced. Model calculations are performed for Ti3+. Two-hump structure in optical absorption band is reproduced without taking into account Jahn-Teller effect. The existence of absorption band in the far-infrared region is demonstrated. Simple procedure to calculate non-radiative transitions probability is developed.