Determination of trapping parameters from thermally stimulated luminescence glow curves of Mn-doped Li2B4O7 phosphor

The determination of trapping parameters such as order of kinetics, activation energy and frequency factor is one of the most important studies in the field of thermally stimulated luminescence (TSL). A polycrystalline sample of Mn-doped Li₂B₄O₇ was prepared by melting method. The formation of the doped compound was checked by Fourier transform infrared study. The TSL study of the Mn-doped lithium tetraborate sample shows two glow peaks at 190 °C and 310 °C, of which the intensity of the 310 °C glow peak is the maximum. In this paper, the trapping parameters associated with the prominent glow peak of Mn-doped lithium tetraborate were reported using the isothermal luminescence decay and glow curve shape (Chen's) methods. Our results show a very good agreement between the trapping parameters calculated by the two methods.     

SrAl_2B_2O_7:Dy~(3+)材料的制备及其发光性能

采用高温固相法制备了SrAl2B2O7:Dy3+发光材料.在350nm紫外光激发下,测得SrAl2B2O7:Dy3+材料的发射光谱为一个多峰宽谱,主峰分别为480,573和678nm;分别和Dy3+的4F9/2→6H15/2,4F9/2→6H13/2,4F9/2→6H11/2的跃迁发射相对应;监测573nm的发射峰,得到材料的激发光谱为一个多峰宽谱,主峰分别为295,325,350,365,400nm.研究了Dy3+掺杂浓度对SrAl2B2O7:Dy3+材料发射光谱的影响,随着Dy3+掺杂浓度的增大,SrAl2B2O7:Dy3+材料的Iy/Ib逐渐增大,根据Judd-Ofelt理论解释了其原因.随着Dy3+掺杂浓度的增大,Dy3+的4F9/2→6H13/2跃迁产生的573nm发射峰强度先增大,在4%时达到最大值,之后减小,其自身的浓度猝灭机理为电偶极-电偶极相互作用.不同的电荷补偿剂Li+,Na+,K+的引入均使发光强度得到提高,尤其以Li+最佳,发光强度提高了大约33%.     

Synthesis and luminescence properties of Na2Ba2Si2O7:Eu2+ phosphor

Green-emitting phosphor Na₂Ba₂Si₂O₇:Eu²⁺ has been synthesized by a conventional high-temperature solid-state reaction. The phase structure and luminescence properties are characterized by the X-ray powder diffraction, diffuse reflectance spectra, photoluminescence excitation and emission spectra, temperature-dependent emission spectra, respectively. It can be efficiently excited in the wavelength range of 325–400 nm and consists of a strong broad green band centered at about 501 nm, which is ascribed to 4f⁶6s⁰5d¹ → 4f⁷6s²5d⁰ transition of Eu²⁺. The critical quenching concentration of Eu²⁺ in the Na₂Ba₂Si₂O₇ host is about 0.8 mol % and corresponding quenching behavior is ascribed to be electric dipole–dipole interaction. Furthermore, the phosphor has good thermal stability property, and the activation energy for thermal quenching is calculated as 0.34 eV.     

High-pressure phase transition of Bi2Fe4O9

The high-pressure behaviour of Bi2Fe4O9 was analysed by in situ powder and single-crystal x-ray diffraction and Raman spectroscopy. Pressures up to 34.3(8) GPa were generated using the diamond anvil cell technique. A reversible phase transition is observed at approximately 6.89(6) GPa and the high-pressure structure is stable up to 26.3(1) GPa. At higher pressures the onset of amorphization is observed. The crystal structures were refined from single-crystal data at ambient pressure and pressures of 4.49(2), 6.46(2), 7.26(2) and 9.4(1) GPa. The high-pressure structure is isotypic to the high-pressure structure of Bi2Ga4O9. The lower phase transition pressure of Bi2Fe4O9 with respect to that of Bi2Ga4O9 (16 GPa) confirms the previously proposed strong influence of cation substitution on the high-pressure stability and the misfit of Ga3+ and Fe3+ in tetrahedral coordination at high pressure. A fit of a second-order Birch–Murnaghan equation of state to the p–V data results in K0 = 74(3) GPa for the low-pressure phase and K0 = 79(2) GPa for the high-pressure phase. The mode Grüneisen parameters were obtained from Raman-spectroscopic measurements.     

Dose effects on the long persistent luminescence properties of beta irradiated SrAl2O4:Eu2+, Dy3+ phosphor

The SrAl₂O₄:Eu²⁺, Dy³⁺ is a phosphor characterized by a long persistent luminescence (PLUM) when it is excited with UV–VIS light and ionizing radiation. In this paper, we study the PLUM behavior as a function of beta irradiation dose in the 0–650 Gy range with a fixed dose rate of 5 Gy/min. The PLUM intensity showed a complex decay behavior, exhibiting a near linear response in the 0–1.7 Gy low dose range and gradually increasing up to 160 Gy. The PLUM reached the saturation for higher doses (>275 Gy) with a slight decrease in the range of 300–650 Gy. In addition, a systematic PLUM enhancement was produced after a thermal cleaning procedure and irradiation at RT in a series of 10 cycles. The observed phenomenon may be related to a radiation-induced process of charge trapping accumulation, which is triggered by thermal stimulation during the irradiation stage. It improves the luminescent characteristics of SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors rendering them suitable for permanent display and illumination devices.     

The luminescence properties of Eu2+ doped Na2CaMg(PO4)2 phosphor

The blue-emitting phosphors of Eu²⁺-doped Na₂CaMg(PO₄)₂ were prepared by high-temperature solid-state reaction. The crystal phase formation was confirmed by X-ray powder diffraction measurement. The luminescence properties were investigated by photoluminescence excitation and emission spectra. The phosphor exhibited the blue luminescence due to the 4f⁶5d¹→4f⁷ transition of Eu²⁺ ions under the excitation of near UV light. The influence of temperature on the luminescence intensities and decay lifetimes of Eu²⁺ was investigated. An unusual increase of the decay lifetimes of the 4f⁶5d emission of Eu²⁺ ion is observed in Na₂CaMg(PO₄)₂ from 10 K to room temperature. The thermal stability of the luminescence of Eu²⁺-doped Na₂CaMg(PO₄)₂ was discussed.     

X-ray excited optical luminescence of Ce-doped BaAl2O4

The luminescence properties of Ce³⁺ in BaAl₂O₄ are reported. The results of simultaneous measurements of XEOL and XAS in the X-ray energy range that includes the Ba L_II,III-edges and Ce L_III edge are shown. The XEOL yield increases as the energy of the photons increases. The radioluminescence spectra, taken from 200 to 1100 nm, showed broad emission bands corresponding to 5d¹→²F_5/2, ²F_7/2 transitions of Ce³⁺ when incorporated into two nonequivalent Ba sites. The lifetime of the light emission was also measured using the single bunch operation mode at the Brazilian National Synchrotron Laboratory (LNLS), and BaAl₂O₄:Ce³⁺ showed single exponential decay time component of about 44.3 ns.     

Electronic structure and luminescence characteristics of rare earth free self-activated Ca2Sb2O7 blue emitting phosphor

Over the past few years, extensive research has been focused on the development of rare-earth-free phosphors to achieve energy-efficient and cost-effective WLEDs with high luminous efficiencies for solid-state lighting applications. Herein, we report a novel rare-earth-free self-activated blue phosphor Ca₂Sb₂O₇, synthesized by solid-state reaction method. The electronic structure and bandgap of the material were determined by the density functional theory (DFT + U) method using Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional. The prepared phosphor could be effectively excited in the range 280–370 nm resulting in a broad blue emission band, owing to the Sb⁵⁺ → O²⁻ transition in the (SbO₆)^7- group. The CIE chromaticity coordinates were found to be (0.144, 0.097) indicating intense blue emission with high color purity of 89%. Also, the prepared phosphor has good thermal stability and an internal quantum efficiency of 24%. All these results indicate that self-activated Ca₂Sb₂O₇ could be a potential blue phosphor for lighting and display devices.     

Recombination luminescence in KI-Tl phosphor

The X-ray luminescence and the optical scintillation of certain specimens of KI-Tl with varying activator content when excited by X-ray radiation at T=105 ° K were studied. The temperatute dependence of the brilliance of scintillation and luminescence measured under pulse conditions was found to be complex, and in the temperature range 105 °–240 ° K a series of alternating increases and decreases in these values was observed. At the same time a definite parallelism was found in the changes in brilliance of the luminescence and the scintillation. An increase in brilliance of specimens excited at 105 ° K after heating up to 133 ° K was observed and investigated. The regularities found are explained by the redistribution of hole centers. The data obtained confirm the importance of the part played by the electron-hole mechanism in the migration of the energy of the basic material to the centers of luminescence in KI-Tl phosphor.     

Self-trapped excitons in LiB3O5 and Li2B4O7 lithium borates: Time-resolved low-temperature luminescence VUV spectroscopy

Results are reported of a coordinated investigation of the dynamics of electronic excitations in LiB₃O₅ and Li₂B₄O₇ crystals by low-temperature luminescence VUV spectroscopy performed with subnano-second resolution under synchrotron photoexcitation. Data on the photoluminescence (PL) decay kinetics, time-resolved PL and PL excitation spectra, and reflectance spectra obtained at 295 and 9.6 K are reported for the first time; the PL of the borates in the 3.5-eV region caused by radiative annihilation of self-trapped excitons (STE) has been established to have an intrinsic nature; the σ and π STE luminescence bands originating from singlet and triplet radiative transitions have been isolated; the shift of the STE σ band relative to the π band has been interpreted; the LBO recombination luminescence band has been isolated; and the creation and decay channels of relaxed and unrelaxed excitons in lithium borates are discussed.     

Synthesis and luminescence properties of red long-lasting phosphor Y2O2S:Eu3+, Zn2+, Ti4+ nanotubes via hydrothermal method

Red long-lasting phosphor Y₂O₂S:Eu³⁺, Zn²⁺, Ti⁴⁺ nanotubes were prepared by hydrothermal method. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence and thermoluminescence spectra (TL) were used to characterize the long-lasting phosphor. XRD investigation revealed that the product synthesised under 750 °C for 6 h was a pure phase of Y₂O₂S. SEM observation showed that the sulfuretted phosphor inherited the tube-like shape from the precursor. Under 325 nm UV excitation, the result indicated the strongest red-emission lines at 627 nm, corresponded to the transition from ⁵D₀ to ⁷F₂ level of Eu³⁺ ion. Both the afterglow decay curves and TL curves revealed that the phosphor had efficient luminescent and excellent long-lasting properties.     

Thermally stable luminescence of blue LiSrPO4:Eu2+ phosphor for near-UV light-emitting diodes

Blue phosphor, LiSrPO₄:Eu²⁺, was prepared by solid-state reaction method under a weak reductive atmosphere and investigated by means of photoluminescence, concentration quenching process, and temperature dependence of luminescence. These results show that LiSrPO₄:Eu²⁺ can be efficiently excited by the UV-visible light of 250–440 nm and exhibits bright blue emission. Furthermore, Eu²⁺-doped LiSrPO₄ phosphor shows high thermally stable luminescence comparable to commercial phosphor BaMgAl₁₀O₁₇:Eu²⁺ (BAM). Two bright blue LEDs were fabricated by incorporating an InGaN-based near-UV chip with the obtained phosphor LiSrPO₄:Eu²⁺ and BAM, respectively. Their luminescence properties were compared based on different forward-bias currents. All the characteristics suggest that LiSrPO₄:Eu²⁺ is a good blue phosphor candidate for creating white light in phosphor-conversion white LEDs.     

A time-resolved luminescence spectroscopy study of non-linear optical crystals K2Al2B2O7

We report the results of complex study of luminescence and dynamics of electronic excitations in K₂Al₂B₂O₇ (KABO) crystals obtained using low-temperature luminescence-optical vacuum ultraviolet spectroscopy with sub-nanosecond time resolution under selective photoexcitation with synchrotron radiation. The paper discusses the decay kinetics of photoluminescence (PL), the time-resolved PL emission spectra (1.2–6.2 eV), the time-resolved PL excitation spectra and the reflection spectra (3.7–21 eV) measured at 7 K. On the basis of the obtained results three absorption peaks at 4.7, 5.8 and 6.5 eV were detected and assigned to charge-transfer absorption from O^2? to Fe³⁺ ions; the intrinsic PL band at 3.28 eV was revealed and attributed to radiative annihilation of self-trapped excitons, the defect luminescence bands at 2.68 and 3.54 eV were separated; the strong PL band at 1.72 eV was revealed and attributed to a radiative transition in Fe³⁺ ion.     

三氧化二镓的高压拉曼光谱研究

β-Ga2O3是一种宽禁带半导体材料(Eg=4.8 eV).研究β-Ga2O3在高压(高应力)条件下的相稳定性和晶格动力学特性对其材料应用具有重要的参考价值.目前关于Ga2O3在高压下的晶格动力学特性研究较少,且Ga2O3的β→α的高压相变压力仍然具有争议.本工作采用基于金刚石压砧(DAC)的高压拉曼光谱技术研究了Ga...     

Preparation and luminescence of blue-emitting phosphor Ca2PO4Cl:Eu2+ for n-UV white LEDs

A series of blue-emitting Ca_2 ? xEu_xPO₄Cl phosphors were synthesized by a solid state method in a reducing atmosphere. The factors those affect the structure and the photoluminescence (PL) intensities of phosphors, including the dosage of chlorine source CaCl₂, reaction time and annealing temperature, have been investigated in detail. X-ray diffraction (XRD) and photoluminescence measurements were performed to testify the crystal structure and luminescent properties. The optimal Eu²⁺ concentration was determined, and the mechanism of the concentration quenching was predominated by dipole–dipole interaction. The present phosphor exhibits a strong absorption in the near-UV region, emits an intense blue emission centered at 451 nm and presents excellent thermal stability, suggesting that the phosphor is competitive as a promising blue-emitting phosphor for near ultraviolet (n-UV) light-emitting diodes (LEDs).     

Eu2+的掺杂浓度对BaAl2Si2O8:Eu2+荧光粉发光特性的影响

采用化学共沉淀法一次煅烧工艺合成了BaAl2Si2O8:Eu2+蓝色荧光粉.用X射线衍射仪和荧光分光光度计等对BaAl2Si2O8:Eu2+蓝色荧光粉的相结构、发光性能进行了测试.结果表明:化学共沉淀法一次煅烧工艺合成的BaAl2Si2O8:Eu2+蓝色荧光粉为单相;其激发光谱分布在240-410 nm的波长范围,峰值位于320 nm处,可以被InGaN管芯产生的350-410 nm辐射有效激发;在365 nm近紫外光的激发下,测得其发射光谱是位于465 nm附近的宽带峰.BaAl2Si2O8:Eu2+蓝色荧光粉的发光强度随Eu2+浓度的增大逐渐加强,当Eu2+掺杂的摩尔分数为3.5%时,发光强度达到最大值,而后随掺杂浓度的增加而减小,发生浓度猝灭;根据Dexter能量共振理论,该浓度猝灭是由于Eu2+的离子间交换相互作用引起的.     

Surface luminescence of a CaO-Mn crystal phosphor

Journal of Applied Spectroscopy -