Ce 3+ and Tb 3+ -doped Na(K)-Gd phosphate glasses were synthesized and their radio-, photo-and th... more Ce 3+ and Tb 3+ -doped Na(K)-Gd phosphate glasses were synthesized and their radio-, photo-and thermoluminescence properties were investigated. Increased radioluminescence e ciency with respect to Gd-free glass matrix has been achieved at Gd concentrations above 20 mol%. This is explained by e cient capture of thermalised electrons and holes in the Gd 3+ -sublattice resulting in the formation of Gd 3+ excited states followed by Gd 3+ -Gd 3+ energy transfer and single-step transfer to the Ce 3+ (Tb 3+ ) emission centres. In such a way non-radiative losses in the phosphate glass matrix are reduced. Energy migration in Gd-sublattice becomes frozen below 10 -15 K due to local ÿeld uctuations in the glass matrix. Thermoluminescence measurements above room temperature show the presence of two groups of traps with concentrations strongly dependent on the glass composition.
The steady-state and time-resolved emission and excitation spectra as well as defects creation sp... more The steady-state and time-resolved emission and excitation spectra as well as defects creation spectra were studied for Pr 3+ -doped Y 3 Al 5 O 12 (YAG) and Lu 3 Al 5 O 12 (LuAG) single crystals at 11-300 K in the 2-12 eV energy range. For Pr 3+ -related UV emission bands located at 3.0-4.2 eV and excited in the band-to-band and exciton absorption regions, additional excitation bands are observed around 6.9-6.35 eV (LuAG) and 6.7-6.25 eV (YAG), which are absent in the undoped crystals and in the excitation spectrum of the intrinsic emission. The wide intrinsic emission observed at 11 K around 4.9 eV, arising from the antisite defects ðLu 3þ Al Þ, is excited only in the exciton band and in the band-to-band absorption region.
ABSTRACT In the temperature range 4.2-350 K, the steady-state and time-resolved emission and exci... more ABSTRACT In the temperature range 4.2-350 K, the steady-state and time-resolved emission and excitation spectra and luminescence decay kinetics are studied for the undoped Y2SiO5 and Lu2SiO5 single crystalline films grown by liquid phase epitaxy method from the PbO-based flux and, owing to that, containing lead ions substituting for Y3+ or Lu3+ ions. Luminescence characteristics of Pb-related centers of different types are identified. On the basis of the results obtained, we suggest that the ultraviolet emission of Pb-related centers arises from the Pb2+ ions substituting for Y3+ or Lu3+ ions in the Y1 and Lu1 lattice sites of the X-2 structure. Possible hypotheses on the origin of the intense complex lead-related blue emission are discussed. We propose phenomenological models describing the excited-state dynamics of the studied luminescence centers. We also determine characteristic parameters of the corresponding relaxed excited states, in particular, the energy separations between the excited states and the rates of the radiative and non-radiative transitions from these states.
Thermally stimulated luminescence (TSL) was studied for many PbWO 4 crystals after their selectiv... more Thermally stimulated luminescence (TSL) was studied for many PbWO 4 crystals after their selective irradiation at 80-220 K in the 3.4-5.0 eV energy range to clarify the origin of the defects responsible for the TSL peaks located in the 200-250 K range. The conclusion is made that both in PbWO 4 and PbWO 4 :Mo crystals the total TSL intensity and the intensity ratio of various TSL peaks are mainly determined by the concentration and type of oxygen and lead vacancies which depend on the crystal preparation and annealing conditions and on the concentration of trivalent rare-earth impurity ions. The TSL peak near 200 K is ascribed to {Pb + .WO 3 } centers and the peak in the 210-230 K range, to the electron centers, containing oxygen vacancies of the type of WO 2 and WO. Only the 250 K peak arises from electron MoO 3− 4 centers. Thermally stimulated processes are accompanied with the green G(II) emission.
Luminescence characteristics of a number of undoped and variously doped PbWO4 crystals were studi... more Luminescence characteristics of a number of undoped and variously doped PbWO4 crystals were studied at 0.4-400 K by the time-resolved spectroscopy and compared with those of ZnWO4; CdWO4 and PbMoO4 crystals. Two types of green emission centres are detected in PbWO4 crystals. The centres of the ÿrst type are responsible for the low-temperature 2.3-2:4 eV emission observed under excitation around 3.90-3:95 eV. The structure and parameters of their relaxed excited states were determined. It was concluded that the origin of defects responsible for the green emission of the ÿrst type could vary for di erent crystals. The centres of the second type with the emission around 2:5 eV appear in crystals containing oxygen vacancies after the thermal destruction of Pb + -WO3 centres at T ¿ 180 K. Decomposition of the exciton and various defect-related states was also studied, and activation energies of this process were calculated.
Luminescence characteristics of a large number of undoped and doped PbWO4 crystals, grown by the ... more Luminescence characteristics of a large number of undoped and doped PbWO4 crystals, grown by the Czochralski or Bridgman method, as-grown or annealed in the nitrogen atmosphere or in air, were studied in the 4.2-300 K temperature range. Two types of red emission centres were found. The centres with the emission band, peaking at 4:2 K at 1:57 eV, were observed in most of the crystals studied. The centres with the emission band, peaking at 4:2 K at 1:48 eV, were observed only in the PbWO4 : Mo 6+ , Y 3+ crystal. It is suggested that incompletely compensated lead vacancies are responsible for the appearance of the red emission.
ABSTRACT Luminescence characteristics of Ce3+- and Pr3+-doped aluminium perovskite (LuAlO3, YAlO3... more ABSTRACT Luminescence characteristics of Ce3+- and Pr3+-doped aluminium perovskite (LuAlO3, YAlO3) and garnet (Lu3Al5O12, Y3Al5O12) single crystalline films, prepared by the liquid phase epitaxy method with the use of the PbO-based flux, were investigated by the time-resolved spectroscopy methods in the 80–300 K temperature range. The influence of various lead-related centers on the characteristics of the Ce3+- and Pr3+-related luminescence centers was studied. It was found that the presence of lead-related centers in the single crystalline films results in a decrease of the quantum efficiency and appearance of undesirable slow components in the luminescence decay kinetics. The possibilities of improving the scintillation characteristics of the single crystalline films were considered.
ABSTRACT Defects formation under UV-irradiation in the impurity-induced absorption bands at 4.2 K... more ABSTRACT Defects formation under UV-irradiation in the impurity-induced absorption bands at 4.2 K has been studied for crystals with and without traps for electrons (CsI:Pb and Eu2+-doped alkali halides, respectively). In both cases the results have been explained by an electron transfer from the impurity-perturbed halogen ion states, resulting in the appearance of electrons and holes in the crystal. In CsI:Pb, the electrons are trapped by lead ions and the holes are self-trapped. In Eu2+-doped crystals, the electrons and the holes recombine with the formation of excitons, whose decay results in the creation of Frenkel defects.
Emission and excitation spectra and decay kinetics are studied for the luminescence of undoped Lu... more Emission and excitation spectra and decay kinetics are studied for the luminescence of undoped LuAG and YAG crystals. Two emission bands are located at 4.8 eV and 3.95 eV in YAG and 4.9 eV and 3.65 eV in LuAG, excited in the Eexc>6.5 eV energy region. They are both characterized by a relatively slow (mus) decay time, and ascribed to
The origin of the centres responsible for the green emission, the processes of their excited-stat... more The origin of the centres responsible for the green emission, the processes of their excited-state disintegration, and the origin of defects created by UV radiation were studied for PbWO 4 crystals with different Mo 6+ concentrations, as well as for the Y 3+ and Nb 5+ co-doped PbWO 4 :Mo. After the selective UV irradiation, TSL appeared to be due to the recombination of defects formed after the exciton and defect-related state disintegration. The TSL intensity versus irradiation energy (3.4-4.3 eV) and irradiation temperature (80-180 K) were measured. For the exciton state disintegration, the activation energy was E a ≅ 0.1 eV, while for the defect states disintegration E a = 0.03-0.36 eV. At T<130 K, temperature-independent defect creation processes were observed in some crystals. Defects of different origins exist in PbWO 4 :Mo crystals, and different defects can coexist in the same sample. Free electron release into the conduction band and also charge transfer processes can contribute to photo-thermally stimulated defects creation.
ABSTRACT Single crystalline films (SCFs) of Y3Al5O12:Bi and Lu3Al5O12:Bi with different Bi3+ cont... more ABSTRACT Single crystalline films (SCFs) of Y3Al5O12:Bi and Lu3Al5O12:Bi with different Bi3+ contents are studied at 1.7–300 K by the time-resolved luminescence spectroscopy methods under excitation in the 2.4–20 eV energy range. The ultraviolet (UV) emission of these SCFs is shown to arise from the radiative decay of the metastable and radiative minima of the triplet relaxed excited state (RES) of a single Bi3+ centre, which are related to the 3P0 and 3P1 levels of a free Bi3+ ion, respectively. At T &lt; 80 K, the radiative decay of the metastable minima is only observed resulting in the appearance of the low-energy component of the triplet emission. At T &gt; 100 K, both the high-energy shift of the maximum and the shortening of the decay time of the UV emission with increasing temperature are caused by thermally stimulated non-radiative transitions between the metastable and radiative minima of the triplet RES. Their excitation bands located around 4.6, 5.2 and 5.95 eV are assigned to the 1S0 → 3P1, 1S0 → 3P2 and 1S0 → 1P1 transitions, respectively, in free Bi3+ ions. The luminescence of dimer Bi3+–Bi3+ centres is not detected in the SCFs studied. The lower-energy (≈2.6 eV) visible (VIS) emission of these SCFs is due to an exciton, localized near a single Bi3+ ion, while the higher-energy (2.75 eV) VIS emission, an exciton, localized near a dimer Bi3+–Bi3+ centre. The phenomenological models are proposed to describe the excited-state dynamics of all the luminescence centres studied. Application of the two- or three-excited-level models on the temperature evolution of the luminescence decay times has allowed determination of characteristic parameters of the corresponding RES: the energy separations between the excited states and the rates of the radiative and non-radiative transitions from these states.
ABSTRACT Emission and excitation spectra, and the luminescence decay kinetics have been studied f... more ABSTRACT Emission and excitation spectra, and the luminescence decay kinetics have been studied for PbCl2 crystals at the temperatures 0.45–100 K. It has been found that even at the lowest temperatures, where the non-radiative decay of exciton states in PbCl2 does not take place, the decay times of both the ultraviolet (UV) and the blue (B) exciton emission are by a few orders of magnitude shorter than the decay times of the emission arising from the triplet relaxed excited state of Pb2+ centres in lead-doped ionic crystals. A conclusion has been drawn that the luminescence of lead halides cannot be connected with single Pb2+ ions. It is proposed that the radiative decay of the self-trapped excitons of the type of {(Pb2)3+ + hole} is responsible for the UV and the B emission of PbCl2 crystals, while the lowest-energy (BG) emission arises from the tunnelling recombinations between the (Pb2)3+-type self-trapped electrons and VK-type self-trapped holes.
ABSTRACT The creation of defects in CsI:Pb crystals by ultraviolet radiation at 4.2 K has been in... more ABSTRACT The creation of defects in CsI:Pb crystals by ultraviolet radiation at 4.2 K has been investigated by thermally stimulated and optically stimulated luminescence methods. The origin of the optically created defects has been established. The dependences of the defect creation efficiency on the irradiation energy and time, on the uniaxial stress, and on the concentration of the impurity (Pb2+ and Na+) ions have been found. The charge-transfer processes taking place under irradiation of CsI:Pb crystals in the Pb2+-related absorption bands and resulting in the appearance of the self-trapped and localized exciton luminescence and in defect creation have been explained.
Photo- and radioluminescence characteristics of the Pr3+-doped Lu3Al5O12 single crystal are repor... more Photo- and radioluminescence characteristics of the Pr3+-doped Lu3Al5O12 single crystal are reported and compared with those of Pr-doped Y3Al5O12. With respect to the Y3Al5O12 host, lower emission quenching and better temperature stability round 300 K is obtained for the Pr3+ 5d-4f emission peaking round 308 nm and about a factor 2 higher radioluminescence intensity is observed around this temperature. The
ABSTRACT Luminescence and vibrational spectroscopies were used to characterize Gd-enriched phosph... more ABSTRACT Luminescence and vibrational spectroscopies were used to characterize Gd-enriched phosphate glasses. In particular, the emission spectrum shows, besides the characteristic 3.98 eV band, an additional band at 3.83 eV, assigned to a vibronic transition. To further support this assignment, Raman spectroscopy measurements were carried out to examine the vibrational response of these glasses. A symmetric stretching of a non-bridging oxygen on a Q2 tetrahedron (PO2) was detected at 1190 cm-1, close to the energy separation between the maxima of 3.98 eV and 3.83 eV bands in the emission spectrum. The emission band at 3.83 eV in Gd-enriched phosphate glasses could be thus intepreted as a vibronic band of the 3.98 eV emission of Gd3+ due to interaction with the (PO2) stretching mode.
The steady-state and time-resolved emission and excitation spectra as well as defects creation sp... more The steady-state and time-resolved emission and excitation spectra as well as defects creation spectra were studied for Pr 3+ -doped Y 3 Al 5 O 12 (YAG) and Lu 3 Al 5 O 12 (LuAG) single crystals at 11-300 K in the 2-12 eV energy range. For Pr 3+ -related UV emission bands located at 3.0-4.2 eV and excited in the band-to-band and exciton absorption regions, additional excitation bands are observed around 6.9-6.35 eV (LuAG) and 6.7-6.25 eV (YAG), which are absent in the undoped crystals and in the excitation spectrum of the intrinsic emission. The wide intrinsic emission observed at 11 K around 4.9 eV, arising from the antisite defects ðLu 3þ Al Þ, is excited only in the exciton band and in the band-to-band absorption region.
Ce 3+ and Tb 3+ -doped Na(K)-Gd phosphate glasses were synthesized and their radio-, photo-and th... more Ce 3+ and Tb 3+ -doped Na(K)-Gd phosphate glasses were synthesized and their radio-, photo-and thermoluminescence properties were investigated. Increased radioluminescence e ciency with respect to Gd-free glass matrix has been achieved at Gd concentrations above 20 mol%. This is explained by e cient capture of thermalised electrons and holes in the Gd 3+ -sublattice resulting in the formation of Gd 3+ excited states followed by Gd 3+ -Gd 3+ energy transfer and single-step transfer to the Ce 3+ (Tb 3+ ) emission centres. In such a way non-radiative losses in the phosphate glass matrix are reduced. Energy migration in Gd-sublattice becomes frozen below 10 -15 K due to local ÿeld uctuations in the glass matrix. Thermoluminescence measurements above room temperature show the presence of two groups of traps with concentrations strongly dependent on the glass composition.
The steady-state and time-resolved emission and excitation spectra as well as defects creation sp... more The steady-state and time-resolved emission and excitation spectra as well as defects creation spectra were studied for Pr 3+ -doped Y 3 Al 5 O 12 (YAG) and Lu 3 Al 5 O 12 (LuAG) single crystals at 11-300 K in the 2-12 eV energy range. For Pr 3+ -related UV emission bands located at 3.0-4.2 eV and excited in the band-to-band and exciton absorption regions, additional excitation bands are observed around 6.9-6.35 eV (LuAG) and 6.7-6.25 eV (YAG), which are absent in the undoped crystals and in the excitation spectrum of the intrinsic emission. The wide intrinsic emission observed at 11 K around 4.9 eV, arising from the antisite defects ðLu 3þ Al Þ, is excited only in the exciton band and in the band-to-band absorption region.
ABSTRACT In the temperature range 4.2-350 K, the steady-state and time-resolved emission and exci... more ABSTRACT In the temperature range 4.2-350 K, the steady-state and time-resolved emission and excitation spectra and luminescence decay kinetics are studied for the undoped Y2SiO5 and Lu2SiO5 single crystalline films grown by liquid phase epitaxy method from the PbO-based flux and, owing to that, containing lead ions substituting for Y3+ or Lu3+ ions. Luminescence characteristics of Pb-related centers of different types are identified. On the basis of the results obtained, we suggest that the ultraviolet emission of Pb-related centers arises from the Pb2+ ions substituting for Y3+ or Lu3+ ions in the Y1 and Lu1 lattice sites of the X-2 structure. Possible hypotheses on the origin of the intense complex lead-related blue emission are discussed. We propose phenomenological models describing the excited-state dynamics of the studied luminescence centers. We also determine characteristic parameters of the corresponding relaxed excited states, in particular, the energy separations between the excited states and the rates of the radiative and non-radiative transitions from these states.
Thermally stimulated luminescence (TSL) was studied for many PbWO 4 crystals after their selectiv... more Thermally stimulated luminescence (TSL) was studied for many PbWO 4 crystals after their selective irradiation at 80-220 K in the 3.4-5.0 eV energy range to clarify the origin of the defects responsible for the TSL peaks located in the 200-250 K range. The conclusion is made that both in PbWO 4 and PbWO 4 :Mo crystals the total TSL intensity and the intensity ratio of various TSL peaks are mainly determined by the concentration and type of oxygen and lead vacancies which depend on the crystal preparation and annealing conditions and on the concentration of trivalent rare-earth impurity ions. The TSL peak near 200 K is ascribed to {Pb + .WO 3 } centers and the peak in the 210-230 K range, to the electron centers, containing oxygen vacancies of the type of WO 2 and WO. Only the 250 K peak arises from electron MoO 3− 4 centers. Thermally stimulated processes are accompanied with the green G(II) emission.
Luminescence characteristics of a number of undoped and variously doped PbWO4 crystals were studi... more Luminescence characteristics of a number of undoped and variously doped PbWO4 crystals were studied at 0.4-400 K by the time-resolved spectroscopy and compared with those of ZnWO4; CdWO4 and PbMoO4 crystals. Two types of green emission centres are detected in PbWO4 crystals. The centres of the ÿrst type are responsible for the low-temperature 2.3-2:4 eV emission observed under excitation around 3.90-3:95 eV. The structure and parameters of their relaxed excited states were determined. It was concluded that the origin of defects responsible for the green emission of the ÿrst type could vary for di erent crystals. The centres of the second type with the emission around 2:5 eV appear in crystals containing oxygen vacancies after the thermal destruction of Pb + -WO3 centres at T ¿ 180 K. Decomposition of the exciton and various defect-related states was also studied, and activation energies of this process were calculated.
Luminescence characteristics of a large number of undoped and doped PbWO4 crystals, grown by the ... more Luminescence characteristics of a large number of undoped and doped PbWO4 crystals, grown by the Czochralski or Bridgman method, as-grown or annealed in the nitrogen atmosphere or in air, were studied in the 4.2-300 K temperature range. Two types of red emission centres were found. The centres with the emission band, peaking at 4:2 K at 1:57 eV, were observed in most of the crystals studied. The centres with the emission band, peaking at 4:2 K at 1:48 eV, were observed only in the PbWO4 : Mo 6+ , Y 3+ crystal. It is suggested that incompletely compensated lead vacancies are responsible for the appearance of the red emission.
ABSTRACT Luminescence characteristics of Ce3+- and Pr3+-doped aluminium perovskite (LuAlO3, YAlO3... more ABSTRACT Luminescence characteristics of Ce3+- and Pr3+-doped aluminium perovskite (LuAlO3, YAlO3) and garnet (Lu3Al5O12, Y3Al5O12) single crystalline films, prepared by the liquid phase epitaxy method with the use of the PbO-based flux, were investigated by the time-resolved spectroscopy methods in the 80–300 K temperature range. The influence of various lead-related centers on the characteristics of the Ce3+- and Pr3+-related luminescence centers was studied. It was found that the presence of lead-related centers in the single crystalline films results in a decrease of the quantum efficiency and appearance of undesirable slow components in the luminescence decay kinetics. The possibilities of improving the scintillation characteristics of the single crystalline films were considered.
ABSTRACT Defects formation under UV-irradiation in the impurity-induced absorption bands at 4.2 K... more ABSTRACT Defects formation under UV-irradiation in the impurity-induced absorption bands at 4.2 K has been studied for crystals with and without traps for electrons (CsI:Pb and Eu2+-doped alkali halides, respectively). In both cases the results have been explained by an electron transfer from the impurity-perturbed halogen ion states, resulting in the appearance of electrons and holes in the crystal. In CsI:Pb, the electrons are trapped by lead ions and the holes are self-trapped. In Eu2+-doped crystals, the electrons and the holes recombine with the formation of excitons, whose decay results in the creation of Frenkel defects.
Emission and excitation spectra and decay kinetics are studied for the luminescence of undoped Lu... more Emission and excitation spectra and decay kinetics are studied for the luminescence of undoped LuAG and YAG crystals. Two emission bands are located at 4.8 eV and 3.95 eV in YAG and 4.9 eV and 3.65 eV in LuAG, excited in the Eexc&amp;amp;amp;amp;amp;amp;amp;gt;6.5 eV energy region. They are both characterized by a relatively slow (mus) decay time, and ascribed to
The origin of the centres responsible for the green emission, the processes of their excited-stat... more The origin of the centres responsible for the green emission, the processes of their excited-state disintegration, and the origin of defects created by UV radiation were studied for PbWO 4 crystals with different Mo 6+ concentrations, as well as for the Y 3+ and Nb 5+ co-doped PbWO 4 :Mo. After the selective UV irradiation, TSL appeared to be due to the recombination of defects formed after the exciton and defect-related state disintegration. The TSL intensity versus irradiation energy (3.4-4.3 eV) and irradiation temperature (80-180 K) were measured. For the exciton state disintegration, the activation energy was E a ≅ 0.1 eV, while for the defect states disintegration E a = 0.03-0.36 eV. At T<130 K, temperature-independent defect creation processes were observed in some crystals. Defects of different origins exist in PbWO 4 :Mo crystals, and different defects can coexist in the same sample. Free electron release into the conduction band and also charge transfer processes can contribute to photo-thermally stimulated defects creation.
ABSTRACT Single crystalline films (SCFs) of Y3Al5O12:Bi and Lu3Al5O12:Bi with different Bi3+ cont... more ABSTRACT Single crystalline films (SCFs) of Y3Al5O12:Bi and Lu3Al5O12:Bi with different Bi3+ contents are studied at 1.7–300 K by the time-resolved luminescence spectroscopy methods under excitation in the 2.4–20 eV energy range. The ultraviolet (UV) emission of these SCFs is shown to arise from the radiative decay of the metastable and radiative minima of the triplet relaxed excited state (RES) of a single Bi3+ centre, which are related to the 3P0 and 3P1 levels of a free Bi3+ ion, respectively. At T &lt; 80 K, the radiative decay of the metastable minima is only observed resulting in the appearance of the low-energy component of the triplet emission. At T &gt; 100 K, both the high-energy shift of the maximum and the shortening of the decay time of the UV emission with increasing temperature are caused by thermally stimulated non-radiative transitions between the metastable and radiative minima of the triplet RES. Their excitation bands located around 4.6, 5.2 and 5.95 eV are assigned to the 1S0 → 3P1, 1S0 → 3P2 and 1S0 → 1P1 transitions, respectively, in free Bi3+ ions. The luminescence of dimer Bi3+–Bi3+ centres is not detected in the SCFs studied. The lower-energy (≈2.6 eV) visible (VIS) emission of these SCFs is due to an exciton, localized near a single Bi3+ ion, while the higher-energy (2.75 eV) VIS emission, an exciton, localized near a dimer Bi3+–Bi3+ centre. The phenomenological models are proposed to describe the excited-state dynamics of all the luminescence centres studied. Application of the two- or three-excited-level models on the temperature evolution of the luminescence decay times has allowed determination of characteristic parameters of the corresponding RES: the energy separations between the excited states and the rates of the radiative and non-radiative transitions from these states.
ABSTRACT Emission and excitation spectra, and the luminescence decay kinetics have been studied f... more ABSTRACT Emission and excitation spectra, and the luminescence decay kinetics have been studied for PbCl2 crystals at the temperatures 0.45–100 K. It has been found that even at the lowest temperatures, where the non-radiative decay of exciton states in PbCl2 does not take place, the decay times of both the ultraviolet (UV) and the blue (B) exciton emission are by a few orders of magnitude shorter than the decay times of the emission arising from the triplet relaxed excited state of Pb2+ centres in lead-doped ionic crystals. A conclusion has been drawn that the luminescence of lead halides cannot be connected with single Pb2+ ions. It is proposed that the radiative decay of the self-trapped excitons of the type of {(Pb2)3+ + hole} is responsible for the UV and the B emission of PbCl2 crystals, while the lowest-energy (BG) emission arises from the tunnelling recombinations between the (Pb2)3+-type self-trapped electrons and VK-type self-trapped holes.
ABSTRACT The creation of defects in CsI:Pb crystals by ultraviolet radiation at 4.2 K has been in... more ABSTRACT The creation of defects in CsI:Pb crystals by ultraviolet radiation at 4.2 K has been investigated by thermally stimulated and optically stimulated luminescence methods. The origin of the optically created defects has been established. The dependences of the defect creation efficiency on the irradiation energy and time, on the uniaxial stress, and on the concentration of the impurity (Pb2+ and Na+) ions have been found. The charge-transfer processes taking place under irradiation of CsI:Pb crystals in the Pb2+-related absorption bands and resulting in the appearance of the self-trapped and localized exciton luminescence and in defect creation have been explained.
Photo- and radioluminescence characteristics of the Pr3+-doped Lu3Al5O12 single crystal are repor... more Photo- and radioluminescence characteristics of the Pr3+-doped Lu3Al5O12 single crystal are reported and compared with those of Pr-doped Y3Al5O12. With respect to the Y3Al5O12 host, lower emission quenching and better temperature stability round 300 K is obtained for the Pr3+ 5d-4f emission peaking round 308 nm and about a factor 2 higher radioluminescence intensity is observed around this temperature. The
ABSTRACT Luminescence and vibrational spectroscopies were used to characterize Gd-enriched phosph... more ABSTRACT Luminescence and vibrational spectroscopies were used to characterize Gd-enriched phosphate glasses. In particular, the emission spectrum shows, besides the characteristic 3.98 eV band, an additional band at 3.83 eV, assigned to a vibronic transition. To further support this assignment, Raman spectroscopy measurements were carried out to examine the vibrational response of these glasses. A symmetric stretching of a non-bridging oxygen on a Q2 tetrahedron (PO2) was detected at 1190 cm-1, close to the energy separation between the maxima of 3.98 eV and 3.83 eV bands in the emission spectrum. The emission band at 3.83 eV in Gd-enriched phosphate glasses could be thus intepreted as a vibronic band of the 3.98 eV emission of Gd3+ due to interaction with the (PO2) stretching mode.
The steady-state and time-resolved emission and excitation spectra as well as defects creation sp... more The steady-state and time-resolved emission and excitation spectra as well as defects creation spectra were studied for Pr 3+ -doped Y 3 Al 5 O 12 (YAG) and Lu 3 Al 5 O 12 (LuAG) single crystals at 11-300 K in the 2-12 eV energy range. For Pr 3+ -related UV emission bands located at 3.0-4.2 eV and excited in the band-to-band and exciton absorption regions, additional excitation bands are observed around 6.9-6.35 eV (LuAG) and 6.7-6.25 eV (YAG), which are absent in the undoped crystals and in the excitation spectrum of the intrinsic emission. The wide intrinsic emission observed at 11 K around 4.9 eV, arising from the antisite defects ðLu 3þ Al Þ, is excited only in the exciton band and in the band-to-band absorption region.
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Papers by A. Krasnikov