B. V. Shulgin

Luminescence excitation of pure and impure BeO single crystals using synchrotron radiation

Abstract Absorption, reflection, UV and VUV luminescence excitation and thermoluminescence excitation spectra have been measured for BeO and BeOZn crystals in the energy range from 8 to 35 eV, using synchrotron radiation. The nature of electronic excitations in the fundamental absorption edge region is discussed; the value of the forbidden-gap energy, E g , is estimated as 10.6 eV for BeO. Intrinsic luminescence with a 6.7 eV maximum for BeO and impurity luminescence with a 6.0 eV maximum for BeOZn are due to the relaxation of both optically created self-trapped or impurity-trapped excitons. The multiplication effect of electronic excitations with E >2 E g (or E ≥2 E ex for 6.7 eV luminescence) for beryllium oxide is due to the inelastic scattering of hot photoelectrons or hot photoholes.

Thermochemical and luminescent properties of the K2MgV2O7 and M2CaV2O7 (M = K, Rb, Cs) vanadates

We have studied the compounds K2MgV2O7 and M2CaV2O7 with M = K, Rb, and Cs. These vanadates melt incongruently in the range 635–717°C. Cooling their decomposition products to room temperature leads to the formation of nonequilibrium phase assemblages characteristic of the corresponding oxide systems. The compounds offer broadband photo- and radioluminescence with an essentially white (to the human eye) emission spectrum. A model is proposed for luminescence centers in the vanadates, which involves the formation of defects in vanadium-oxygen groups, and an energy level diagram of the emission centers is constructed in the form of configuration curves in the harmonic oscillator approximation. The luminescent properties of these compounds suggest that they can be used as basic components of cathodo- and roentgenoluminescent screens and white-light-emitting diodes with improved color performance.

Research of energy transfer in Y2SiO5Ce, Tb single crystals by time resolved luminescence spectroscopy

Abstract The energy transfer between the rare-earth ions in Y s SiO 5 Ce, Tb crystals has been investigated with the use of the methods of luminescence spectroscopy with subnanosecond time resolution and excitation by pulsed synchrotron radiation (SR). Effective nonradiative energy transfer between Ce 3+ and Tb 3+ -ions which is realized by the inductive resonance mechanism has been observed. The absolute constant of the energy transfer speed K t and the probability of transfer have been determined. A dependence of the energy transfer parameters on the SR-excitation density has been discovered and investigated. Increasing of the density of the SR-excitation by a factor of 10 results in the increase of K t from 4.8 × 10 8 up to 1.7 × 10 10 mol −1 s −1 .

Radioluminescent properties of Eu2+-doped aluminum oxynitride

X-ray luminescence (XRL) and pulsed cathodoluminescence (PCL) spectra of Eu2+-doped aluminum oxynitride Al5O6N (prepared using the standard sol-gel technique) have been investigated. The radioluminescence spectra, concentration dependences of light yield and time parameters of luminescence process have been measured and discussed. Some peculiarities of luminescence spectra as well as the possible excitation mechanism of AL5O6N with Eu2+ dopants are discussed too.

Hexametavanadates M4+M2+(VO3)6: Thermal stability and luminescent characteristics

Rhombohedral hexametavanadates K4Sr(VO3)6, K4Ba(VO3)6, Rb4 Ba(VO3)6, and Cs4Ba(VO3)6 melt incongruently in the temperature range of 491 to 600°C. Cooling of peritectic melts yields mixtures of compounds typical of M2+O-M2+O-V2O5 systems, far from equilibrium and depending on the cooling kinetics. The vanadate Cs4Ba(VO3)6 undergoes reversible polymorphic transformation at 360°C. All compounds show broad-band luminescence with a maximum of the luminescence spectrum at 490–590 nm with three types of excitation. The vanadates K4Sr(VO3)6 and Rb4Ba(VO3)6 show the highest luminescence intensity at room temperature. The latter is also most efficient at liquid nitrogen temperatures. The luminescence spectra depend on the excitation of vanadates. Three hypotheses were put forward to interpret this finding. The nature of luminescence is attributed to the relaxation of electronic excitation in [VO4]3− structural tetrahedra present in the vanadates. The performance characteristics of luminophores were determined. These luminophores may be promising as X-ray luminescent screens, radioluminescence indicators, and light-emitting diode devices.

Luminescent properties of Eu2+ in AlON, SiAlON, Ca-SiAlON oxynitrides

The X-ray luminescence (XRL) properties of γ-AlON (γ-Al5O6N), β-SiAlON (Si6–nAlnOnN8–n, where n = 2 and 3) and Ca-α-SiAlON (Cam/2Si12−(m+n)Alm+nOnN16−n) oxynitride samples doped by Eu2+ were investigated. The strong correlation of luminescence spectra parameters of Eu2+ luminescence centers in dependence of oxynitride samples composition is observed. With fitting procedure the composition of XRL spectra with complex profile of investigated oxynitride samples of γ-AlON, β-SiAlON and Ca-α-SiAlON was identified and discussed.The X-ray luminescence (XRL) properties of γ-AlON (γ-Al5O6N), β-SiAlON (Si6–nAlnOnN8–n, where n = 2 and 3) and Ca-α-SiAlON (Cam/2Si12−(m+n)Alm+nOnN16−n) oxynitride samples doped by Eu2+ were investigated. The strong correlation of luminescence spectra parameters of Eu2+ luminescence centers in dependence of oxynitride samples composition is observed. With fitting procedure the composition of XRL spectra with complex profile of investigated oxynitride samples of γ-AlON, β-SiAlON and Ca-α-SiAlON was identified and discussed.