Luminescence and scintillation properties of advanced Lu3Al5O12:Pr3+ single crystal scintillators

In this paper we present the luminescence and scintillation properties of Lu₃Al₅O₁₂:Pr (LuAG:Pr) single crystals with Pr³⁺ concentration of 0.13 wt %, grown by the Czochralski method. The light yield and energy resolution were measured under 662 keV γ-ray excitation. The dominant emission band peaking at 310 nm with a shoulder at 370 nm was observed in the photoluminescence spectrum. High light yield of 24,500 ph/MeV and an energy resolution of 5.3 % were obtained for a 6 × 6 × 2 mm³ LuAG:Pr sample. Light yield dependence on sample height and shaping time was measured. The estimated photofraction in pulse height spectrum and total mass attenuation coefficient at 662 keV γ-rays were also determined and compared with the theoretical ones calculated using the WinXCom program.     

Comparison of Lu3Al5O12:Pr and Bi4Ge3O12 scintillators for gamma-ray detection

The scintillation properties of Lu₃Al₅O₁₂:Pr³⁺ (LuAG:Pr) single crystal grown by the Czochralski method with praseodymium concentration of 0.19 mol% were investigated. For a comparison, a good quality Bi₄Ge₃O₁₂ (BGO) single crystal grown by Bridgman method was also studied. The light yield and energy resolution were measured using photomultiplier tube (XP5200B PMT) readout. Moderate light yield of 15,900 photons per MeV was measured for the LuAG:Pr(0.19%) crystal. For 662 keV gamma rays (¹³⁷Cs source), an energy resolution of 6.5% obtained for LuAG:Pr(0.19%) is much better than that of 9.0% obtained for BGO. The light yield non-proportionality and energy resolution versus energy of gamma rays were measured and the intrinsic resolution of the crystals was determined after correcting the measured energy resolution for PMT statistics. The LuAG:Pr(0.19%) showed a good proportionality of the light yield within 5% over the energy range from 1274.5 keV down to 32 keV, which is much better than that of 14% for BGO. The photofraction was determined at 320 and 662 keV for both crystals and compared with the ratio of the cross-sections for the photoelectric effect to the total one calculated using WinXCOM program.     

Luminescence and scintillation properties of Lu0.8Gd1.2SiO5:Ce and Lu1.8Gd0.2SiO5:Ce single crystals: A comparative study

The luminescence and scintillation properties of Lu_0.8Gd_1.2SiO₅:Ce and Lu_1.8Gd_0.2SiO₅:Ce single crystals are compared. At 662 keV γ-rays, light yield (LY) value of 29,800 ph/MeV obtained for Lu_1.8Gd_0.2SiO₅:Ce is much higher than that of 20,200 ph/MeV obtained for Lu_0.8Gd_1.2SiO₅:Ce. The energy resolution of 6.0% obtained for Lu_0.8Gd_1.2SiO₅:Ce is better than that of 7.7% for Lu_1.8Gd_0.2SiO₅:Ce due to its better intrinsic resolution and proportionality of LY. The LY and energy resolution for α-rays, as well as a LY ratio under excitation with α- and γ-rays (α/γ ratio) are also determined. The intrinsic LY and light loss coefficient under excitation with α- and γ-rays are evaluated. The photofraction at 662 keV γ-rays is also determined and discussed.     

Luminescent properties and energy transfer of Y3Al5O12:Ce3+, Ln3+ (Ln=Tb,Pr) prepared by polymer-assisted sol–gel method

Y₃Al₅O₁₂:Ce³⁺, Pr³⁺ and Y₃Al₅O₁₂:Ce³⁺, Tb³⁺ nano-particles have been synthesized by polymer-assisted sol–gel method. Crystal structure, luminescent properties and energy transfer of the phosphors are analyzed. XRD study of polycrystalline powders shows that all the samples are of YAG phase without impurity. Photoluminescence (PL) emission and excitation spectra illustrate that in YAG:Ce, Pr phosphors, energy transfer occurs mutually between Ce³⁺ and Pr³⁺, while in YAG:Ce, Tb systems, only one-way path energy transfer of Tb³⁺→Ce³⁺ is observed.     

YAG:Pr3+的真空紫外光谱分析及其4f5d能级的研究

用共沉淀法制备出不同掺杂浓度的钇铝石榴石(Y₃Al₅O_{12，YAG)：Pr³⁺粉末.在不同温度下用同步辐射的真空紫外光(VUV)作为激发光 源测量了其发射和激发光谱.对YAG：Pr³⁺被VUV激发后的发光过程进行了分析， 并估算了YAG：Pr³⁺的声子能量、黄昆因子S及Stokes位移.当用170nm光激发样 品时，可能存在自陷激子和通过自陷激子能量传递引发的³P0发射 ，这种跃迁途径不同于用240nm和289nm两个波长激发后的跃迁途径；对Pr³⁺在Y AG中的4f5d能级进行了研究，从而对其4f5d组态有了一个较清晰的认识. 关键词： 3+')" href="#">YAG：Pr³⁺ 同步辐射 4f5d能级 VUV}     

Energy transfer and excitation wavelength dependent long-lasting phosphorescence in Pr activated Y3Al5O12

Long-lasting phosphorescence (LLP) was observed in Pr³⁺-doped Y₃Al₅O₁₂ (YAG:Pr) after it was excited by 240 or 290 nm light. The photoluminescence (PL) and LLP properties were studied. It is interesting that the PL and LLP spectra were different. In the PL emission spectra both the emissions of d-f and f-f transitions of Pr³⁺ ions were observed. However, in the LLP spectra of YAG:Pr the emissions of d-f transition were absent. It is deduced that the differences were due to the energy transfer process between traps and emission centers. On the other hand, significant differences were observed between the two LLP spectra after the sample was excited by 240 and 290 nm lights, respectively. The thermoluminescence (TL) properties were also studied. It is suggested that these studies will be significant for understanding the mechanism of LLP phenomenon.     

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 (¹ S→¹ I ₆ transitions) and the second (transitions from the ³ P ₀ level to the ³ H and ³ F 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 ¹ S ₀, 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.     

Energy transfer-based spectral properties of Tb-, Pr-, or Sm-codoped YAG:Ce nanocrystalline phosphors

Tb³⁺-, Pr³⁺-, or Sm³⁺-codoped YAG:Ce nanocrystalline phosphors were prepared using a modified polyol process. Possible tunability of Ce³⁺-related yellow emission in codoped YAG:Ce nanocrystalline systems was investigated. Dual emission of yellow and red spectral component with a single excitation wavelength was observed from YAG:Ce, Pr or YAG:Ce,Sm codoped systems via an energy transfer from Ce³⁺ and Pr³⁺ or Sm³⁺ ion. It was also observed that the energy transfer event in YAG:Ce, Pr nanocrystalline phosphor occurs mutually between Ce³⁺↔Pr³⁺, while in YAG:Ce, Sm and YAG:Ce, Tb the energy transfer progresses one way. The detailed pathways for transferring an excitation energy are explained based on the energy level diagrams of respective Ce³⁺, Pr³⁺, Sm³⁺, Tb³⁺ ion.     

Ultraviolet spectroscopy of Pr+3 and its use in making ultraviolet filters

Sputtered deposited thin films of AlN:Pr and GaN:Pr emit in ultraviolet–visible and visible regions of the spectrum, respectively, under electron excitation in cathodoluminescence apparatus. The goal is to study the ultraviolet emission from Pr⁺³ when doped in nitride semiconductor hosts. Luminescence peaks at a wavelength of 295 nm (4.2 eV), 335 nm (3.7 eV) and 385 nm (3.24 eV) are observed as a result from ¹S₀ → ¹G₄, ¹S₀ → ¹D₂ and ¹S₀ → ¹I₆ transitions, respectively. However the ¹S₀ → ¹G₄ and ¹S₀ → ¹D₂ transitions are not observed when Pr⁺³ is doped in GaN host. The bandgap of GaN absorbs the ultraviolet radiation emitted from Pr⁺³ and hence GaN can be used as ultraviolet filter for radiation shielding and protection purposes. AlN is transparent to ultraviolet due to its wide bandgap of 6.2 eV.     

Luminescence of CaWO4:Pr3+ and CaWO4:Tb3+ at ambient and high hydrostatic pressures

Photoluminescence spectra of CaWO₄ doped with Pr³⁺ and Tb³⁺ obtained at high hydrostatic pressures up to 315 kbar applied in a diamond anvil cell (DAC) are presented. The intensities of the luminescence from the ³P₀ state of Pr³⁺ and from the ⁵D₃ state of Tb³⁺ decreased with increasing pressure. At pressures greater than 50 kbar, the ¹D₂ → ³H_J transitions in Pr³⁺ and the ⁵D₄ → ⁷F_J transitions in Tb³⁺ dominated the spectra. At pressures greater than 100 kbar, only emissions from the lower excited states were observed. At pressures greater than 150 kbar, luminescence from the ¹D₂ and ⁵D₄ states also decreased with increasing pressure, and at a pressure of 315 kbar for CaWO₄:Pr³⁺ and 190 kbar for CaWO₄:Tb³⁺, the emissions related to the Pr³⁺ and Tb³⁺ were quenched. These effects were related to the influence of impurity trapped excitons (ITEs) on the efficiency of the f–f emission in the Pr³⁺ and Tb³⁺ ions. Analysis of the emission spectra collected at different pressures allowed the energies of the ground states of the Pr³⁺ and Tb³⁺ ions with respect to the band edges of the CaWO₄ host to be estimated.     

Spectral-kinetic characteristics of Pr luminescence in LiLuF4 host upon excitation in the UV-VUV range

Spectral-kinetic study of Pr³⁺ luminescence has been performed for LiLuF₄:Pr(0.1 mol%) single crystal upon the excitation within 5-12 eV range at T=8 K. The fine-structure of Pr³⁺ 4f ²→4f 5d excitation spectra is shown for LiLuF₄:Pr(0.1 mol%) to be affected by the efficient absorption transitions of Pr³⁺ ions into 4f 5d involving 4f ¹ core in the ground state. Favourable conditions have been revealed in LiLuF₄:Pr(0.1 mol%) for the transformation of UV-VUV excitation quanta into the visible range. Lightly doped LiLuF₄:Pr crystals are considered as the promising luminescent materials possessing the efficient Pr³⁺³P₀ visible emission upon UV-VUV excitation. The mechanism of energy transfer between Lu³⁺ host ion and Pr³⁺ impurity is discussed.     

Levels in182W populated in the decay of182Ta

Theγ-rays emitted in theβ-decay of¹⁸²Ta have been reinvestigated with improved statistics in attempting to clarify the reported new levels at 1460.41, 1592.98, 1620.36, 1712.29 and 1762.91 keV in¹⁸²W observed in theβ-decay of¹⁸²Ta. The present study demonstrated that the fifteen newγ-rays, which were used to support the existence of the five new levels, are not relevant to theγ-decay of¹⁸²Ta. Therefore the five new levels are not populated in this decay. Additionally, theγ-ray with an energy of 1035.6 keV (0 ₂ ⁺ →2 ₁ ⁺ ) deexciting theβ-band head in¹⁸²W is observed for the first time in the present decay study and the previous tentative placement of the 351.0 keVγ-ray in the level scheme is confirmed by the present coincidence measurements.     

Intense orange emission in Pr3+ doped lead phosphate glass

Spectroscopic properties of one mol% Pr₂O₃ embedded in 40%PbO–60%P₂O₅ glass have been investigated at room temperature. From the absorption spectra energy levels of the observed bands are assigned. Using free ion Hamiltonian theoretical values of energy of 13 multiplets of Pr³⁺ are calculated. Judd–Ofelt intensity parameters have been estimated by including and excluding the hypersensitive transition (³H₄→³P₂). The best set of Judd–Ofelt parameters are obtained by omitting ³H₄→³P₂ transition from the calculation. These parameters are used to evaluate the important laser parameters for various emission lines. Our investigation reveals that the present glass may be utilized as a laser active medium corresponding to ³P₀→³H₄ and ¹D₂→³H₄ transitions respectively, for 484.6 nm (blue) and 599.5 nm (strong orange) emissions. Indirect and direct optical band gap energies of Pr³⁺ doped lead phosphate glass matrix have also been reported.     

Measurement of the 50Cr(γ, n)49Cr cross section with monochromatic γ-rays

The ⁵⁰Cr(γ, n)⁴⁹Cr cross section has been measured over the energy range E_γ = 20.43 to E_γ = 22.22 MeV using monochromatic γ-rays from the ³H(p, γ)⁴He reaction and detecting the resulting ⁴⁹Cr positon activity. The γ-rays were monitored by a 12.7 cm × 15.2 cm NaI(Tl) crystal. The positon activity was determined by a coincidence detector consisting of two 7.62 cm × 7.62 cm NaI(Tl) crystals set on the annihilation radiation photopeaks. The γ-ray energy resolution was less than 110 keV over the whole energy range. Structure in the cross section was not observed.     

Energy transfer induced Eu3+ photoluminescence enhancement in tellurite glass

In this work, structural, thermal and optical properties of Eu³⁺ doped TeO₂–La₂O₃–TiO₂ glass were investigated. The differential scanning calorimetry (DSC) measurements reveal an important stability factor ΔT=143.52 K, which indicates the good thermal and mechanical stabilities of tellurite glass. From the absorption spectrum, the optical band gap was found to be direct with E_g=3.23 eV. The temperature dependences of photoluminescence (PL) properties of Eu-doped and Eu–Tb codoped tellurite glass are investigated. As the temperature increases from 7 to 300 K, both the PL intensity and the PL lifetime relative to the ⁵D₂→⁷F₀ are nearly constant below 230 K and then an enhancement takes place. This anomalous feature is attributed to the thermally activated carrier transfer process from charged intrinsic defects states to Eu³⁺ energy levels.By co-doping tellurite glasses with Eu and Tb, a strong Eu³⁺ PL enhancement is shown due to excitation transfer from Tb³⁺ and intrinsic defects to Eu ions.     

The 1S0 emission from the minor site of Pr3+ in (Ba,La)F2:Pr

In this paper we present and discuss results of detailed spectroscopy studies of Pr³⁺ luminescence from the (Ba,La)F₂:0.2 m%Pr crystals under UV and VUV synchrotron excitation.We have measured time resolved emissions from the minor site Pr³⁺ in (Ba,La)F₂:Pr at 10 and 300 K. The spectra clearly show the ¹S₀ emission from the Pr³⁺ ions in some low symmetry Pr-sites (we designate them La-sites) previously identified in higher concentration (0.3 m%Pr and more) crystals. However most of emission from the Pr activated (Ba,La)F₂ crystals originates in Pr³⁺ ions in other sites which produce an efficient d-f emission. As demonstrated by excitation spectra, the emission from some of these sites (denoted as Ba-sites) closely resembles the d-f emission from BaF₂.The La-site, time resolved and long delay emission spectra are dominated by hypersensitive transitions from the ¹S₀ and ³P₀ levels to lower energy levels of the 4f² configurations. Only these transitions contribute to the photon cascade emission desired for some mercury free phosphor applications.     

Effect of interface states associated with transitional nanophase precipitates in the enhancement of red emission from SrAl12O19:Pr by Ti incorporation

SrAl₁₂O₁₉:Pr³⁺, Ti⁴⁺ phosphor suitable for field emission displays is prepared by the wet chemical gel-carbonate method and the mechanism of enhancement in red photoluminescence (PL) intensity with Ti⁴⁺ therein has been investigated. The PL spectra of Pr³⁺ show both ¹D₂-³H₄ and ³P₀-³H₆ emission in the red region with very weak intensity when excited at 355 nm. The emission intensity has increased by about 100 times at room temperature in the compositional range SrAl_12−xTi_xO_19+x/2:Pr³⁺, with 0.1≤x≤0.3 in comparison to Ti-free SrAl₁₂O₁₉:Pr³⁺. TEM investigations show the presence of exsolved nanophase of SrAl₈Ti₃O₁₉, the precipitation of which is preceded by the presence of defect centers at the interfacial regions between the semicoherent transient phase and the parent SrAl₁₂O₁₉ matrix. The presence of transitional nanophase and the associated defects modify the excitation-emission process by way of formation of electronic sub-levels at lower energy (3.5 eV) than the band gap of SrAl₁₂O₁₉ (∼7 eV) followed by non-resonance energy transfer to Pr³⁺ level, leading to magnetic-dipole related red emission with enhanced intensity. The PL intensity of Pr³⁺ decreases at high Ti⁴⁺ concentrations (x>0.3) due to higher extent of segregation of non-emissive SrAl₈Ti₃O₁₉:Pr³⁺ phase.     

Photoluminescence characteristics of Pr3+ in ThO2: interplay of defects in a photo-induced charge transfer

Photo-luminescence studies of Pr³⁺ activated thorium oxide phosphor have revealed that mainly ³P→³H₄ and ¹D₂→³H₄ transitions with life-time of 30 and 600 μs are observed in this sample. An exponential reduction in the emission intensity of Pr³⁺ ions was observed on following continuous excitation with 275 nm corresponding to the f–d transition band of Pr³⁺ ions. Such a reduction in emission intensity was observed at all temperatures investigated in the range 90–330 K. The emission intensity recovered partially on dark storage only above 180 K. The recovery of emission intensity was also observed on the illumination of pre-exposed sample to light in the wavelength region 300–430 nm. Following illumination with 275 nm, Pr³⁺ activated thorium oxide phosphor has displayed a weak thermally stimulated luminescence. These results thus suggest that the optical excitation dynamically changes the state of the system under observation, and that changes are occurring in the valence state of Pr ions due to e/h transfer process on 275-nm exposure. On dark storage and also on 365-nm illumination of the pre-exposed sample, e/h traps recombine to cause emission signal recovery. The analysis of data on reduction in intensity obtained with exposure to 275 nm suggests the likelihood of the of Pr³⁺ ions existing at three different sites. The activation energies associated with the release of electrons from excited Pr³⁺ ions at different sites were determined from the temperature dependence of the photo-induced charge transfer process.     

Resonant processes causing photon multiplication in CaSO4:Tb3+

The emission spectra of single and polyterbium centers have been measured at the excitation of CaSO₄:Tb³⁺ phosphors with different charge compensators (Na⁺, calcium vacancies, etc.) by 3.8–35 eV photons or 5 and 300 keV electrons at 6–300 K. The possible mechanisms providing quantum yield above unity for green (⁵D₄ → ⁷F_J) and blue emission (⁵D₃ → ⁷F_J) of Tb³⁺ at the direct intracenter excitation, excitation of oxyanions or creation of hot (nonrelaxed) electrons and holes have been discussed. On the basis of thermally stimulated luminescence at 6–600 K, the peculiarities of the hopping diffusion of relaxed electrons and holes and their tentative low-temperature self-trapping have been considered.     

The decay of the 11.80 MeV isobaric analog resonance in93Tc to negative parity states in92Mo

The 2,524 keV 5^? state and 2,848 keV3^? state in⁹²Mo were excited by inelastic proton scattering going through the 11.80 MeV isobaric analog resonance in⁹³Tc. Angular distributions of the 3^?→ 2⁺ and 5^?→ 4⁺ γ-rays were measured and analyzed in order to obtain the partial waves of the outgoing protons.