A. S. Potapov

Emission of Pr3+ in SrAl12O19 under vacuum ultraviolet synchrotron excitation

SrAl12O19:Pr phosphors have been investigated under ultraviolet/vacuum ultraviolet (5?20 eV) synchrotron radiation at room and near liquid He temperatures. The excitation of 1S 0 ?1I 6 and 3P 0 ?3H 4 emission of Pr3+ in SrAl12O19 occurs in a 1 eV wide region originating from the interconfiguration 4f2 ? 4f5d transitions with threshold (onset of the transitions) at 6.0 eV at room temperature and at 6.15 eV at 14 K. A comparison of the excitation spectra of Pr3+ and known data for Ce3+ in SrAl12O19 reveals a shift of 1.52 eV between 5d states of the ions. The next threshold near 7.5 eV corresponds to the transitions from valence to conduction band. The luminescence from the 3P 0 level is excited efficiently at low temperature while 1S 0 luminescence is absent under band-to-band excitation. To explain this, a mechanism involving valence hole trapping and energy transfer from excitonic states to Pr3+ is proposed. At excitation near the maximum of 4f2 ? 4f5d transitions (6.4 eV), the 1S 0 ?1I 6 luminescence exhibits exponential decay with constant ? = 330 ? 10 ns at 300 K and ? ? 400 ns at 14 K. At pre-threshold excitation (E < 6.0 eV) a fast component ? ? 10 ns originating from excitonic emission prevails.

Quest and investigation of long wavelength scintillators

Abstract Scintillation characteristics such as spectra, decay times and yields of Cu- and Ag-doped ZnS x Se 1− x solid solutions, Tb-doped Gd 2 O 2 S and Y 2 O 2 S ceramics, Al 2 O 3 :Ti single crystal, and some other compounds have been measured under X-ray excitation. Certain investigated materials show a high light yield in the long wavelength region and adequate kinetic properties. It is shown that the light yield can be increased for compounds synthesized at optimal conditions.

Luminescence characteristics of the Pr3+ ion in SrB4O7 and SrB6O10

Spectral and kinetic characteristics of the luminescence and luminescence excitation spectra of polycrystalline SrB4O7:Pr (1%) and SrB6O10:Pr (1%) samples are studied at 150–170 K. The samples show an intense luminescence band in the vicinity of 405 nm (1S0→1I6 transitions of Pr3+) and shorter wavelength bands also assigned to transitions from the 1S0 level. The main luminescence decay constant is ∼2×10−7 s. The excitation spectra of the 1S0 luminescence in these crystals are significantly different. The SrB4O7:Pr crystal shows three well-resolved bands at 6.14, 6.55, and 6.91 eV in the region of the 4f2→4f15d transitions and a complex structure in the region of interband transitions (7.1–20 eV), whereas the SrB6O10:Pr crystal shows a weakly structured band at 6.31 eV and no excitation in the region of the interband transitions. The physical mechanisms that may be responsible for the observed features of the spectra are discussed.

Praseodymium luminescence in fluorides

This work is a continuation of studies of the Pr3+ cascade emission in various matrices. The effect of the environment of the luminescence center on the mutual position of the lowest 5d and the 4f level 1S0 of Pr3+ is considered. PrF3 clustering in BaF2 is observed at a high praseodymium concentration. The promising potential of magnesium as a charge compensator for praseodymium in SrAlF5 is demonstrated.

Search for new long-wavelength phosphors

At present there is a great interest in phosphors producing high light yield in long wavelength region (550 - 1050 nm). They have a lot of application in different fields of physics such as laser physics, medical physics and tomography, semiconductor physics and others. The main reason of that is the emission spectra of these materials match well to sensitivity of silicon photodiodes. In this paper we present the spectral and decay time characteristics of some long-wavelength phosphors (such as AIIBVI, Al2O3:Ti, some molybdates, Gd2O2S and Y2O2S doped with Tb, and some others). The process of energy transfer to emission centers are considered. In most cases, types of the centers responsible for radiative transitions were determined.

Spectral and kinetic characteristics of trivalent praseodymium in LaF3-LiF and SrAl12O19

Recent data on cascade transitions in the 4f shell of the Pr3+ ion in various matrices are analyzed. Spectral and kinetic characteristics of LaF3-LiF:Pr and SrAl12O19:Pr phosphors, which show photon cascade emission, were investigated. The emission intensities in the first (1S→1I6 transitions) and the second (transitions from the 3P0 level to the 3H and 3F multiplets) cascade stages were measured and the temperature dependences of the intensities of the main emission lines and their kinetic characteristics were determined. The following parameters of SrAl12O19:Pr were found: the band gap width (7.5 eV), the energy gap between the 1S0, 4f and 5d levels (0.24 eV), and the characteristics of the 4f→5d band (6.0–7.5 eV) of the Pr3+ luminescence excitation. It is shown that the LaF3-LiF:Pr compound has a number of specific features in comparison with other Pr3+-doped phosphors.

Temperature-induced variation of the emission band intensities of an SrAl12O19:Pr phosphor

The spectral characteristics of the X-ray-excited luminescence from an SrAl12O19:Pr phosphor featuring cascade photon emission were studied in a range of temperatures from 90 to 500 K. It is demonstrated that an important role in the energy transfer to the emission centers in SrAl12O19:Pr is played by competitive processes of the formation of Vk centers and the trapping of holes by Pr3+ ions.

The development of new phosphors with high quantum efficiency

This paper discusses various physical mechanisms that result in cascade photon emission. It is shown to be promising to use the Pr3+ ion as an activator for creating phosphors with a quantum efficiency greater than unity. The properties of the phosphors SrAl12O19:Pr and SrAlF5:Pr are discussed.

Effect of various impurities on luminescent properties of cerium fluoride

Scintillation properties of cerium fluoride crystals doped with different di-, tri-, and four-valent cations have been studied. Luminescence spectra, light output and kinetics have been measured. The influence of the valence state of the impurity on the scintillation properties of cerium fluoride is 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.