Xinguang Ren

Modified photoluminescence properties of rare-earth complex/polymer composite fibers prepared by electrospinning

Efficiently luminescent composite fibers of poly (vinyl pyrrolidone) (Mw≈1300000) and europium complex Eu(TTA)3(TPPO)2 (TTA is thenoyltrifluoroacetone; TPPO is triphenylphosphine oxide) were prepared by electrospinning, with average diameters of 200–500nm and lengths of several tens of micrometers. Their photoluminescence properties were studied in comparison to the pure Eu(TTA)3(TPPO)2 complex. It was significant to observe that the thermal stability of photoluminescence in the composite fibers was improved considerably over the pure complex.

Enhanced red phosphorescence in nanosized CaTiO3:Pr3+ phosphors

The red photoluminescence and phosphorescence originating from D21-H43 transition of Pr3+ in CaTiO3 nanoparticles are studied as a function of Pr3+ concentrations. The nanophosphors exhibit both longer persistence time of 30min and higher quenching concentration of 0.4mol% than the bulk (10min and 0.1mol%). The initial phosphorescence in the nanophosphor is an order of magnitude stronger than that in the bulk at the corresponding quenching concentrations. Phosphorescence decay patterns and diffused reflectance spectra before and after ultraviolet exposure indicate the existence of more traps contributing to phosphorescence in the nanoparticles.

Mn2+ concentration manipulated red emission in BaMg2Si2O7 : Eu2+,Mn2+

The luminescent properties of concentration dependence are reported in BaMg2Si2O7:Eu2+,Mn2+ red phosphor. It is observed that the broad red emission of Mn2+ consists of two bands, located at 620 and 675 nm, respectively, which are attributed to two different Mn2+ centers [Mn2+(I) and Mn2+(II)] substituting for two nonidentical Mg2+ sites [Mg2+(I) and Mg2+(II)] in the host. It is also found that the relative emission intensity of the Mn2+(II) to the Mn2+(I) increases with increasing Mn2+ concentration, leading to a red-shift of the overall emission. A detail analysis on the energy transfer from Eu2+ to the two Mn2+ centers is presented, which indicates that the number ratio of Mn2+(II) to Mn2+(I) increases with increasing Mn2+ concentration. This result is interpreted by the preferential formation of Mn2+(I) substituting for Mg2+(I) site. Based on energy transfer, the emission intensity ratios of Mn2+(I) to Eu2+ and Mn2+(II) to Eu2+, which is Mn2+ concentration dependent, are calculated using related fluor...

Mn2+ activated red phosphorescence in BaMg2Si2O7: Mn2+, Eu2+, Dy3+ through persistent energy transfer

Based on persistent energy transfer, Mn2+ activated red phosphorescence is achieved in BaMg2Si2O7. Two types of Mn2+ centers with emitting peaks at 620 and 675nm, respectively, are observed and found to govern both the red luminescence and red phosphorescence spectral shapes. The spectral distribution of the red phosphorescence as a function of irradiation wavelengths and Mn2+ concentrations is systematically studied in Mn2+ and Dy3+ doubly doped and Mn2+, Eu2+, and Dy3+ tridoped samples, indicating the dominant role of persistent energy transfer on generation of the red phosphorescence. Moreover, it is found that the incorporation of Mn2+ in BaMg2Si2O7: Eu2+, Dy3+ may prolong the phosphorescent persistence time (>1h) compared with the Mn2+ free materials.

Evidence for visible quantum cutting via energy transfer in SrAl12O19 : Pr, Cr

Evidence for visible quantum cutting involving the emission of two visible photons for each vacuum-ultraviolet (VUV) photon absorbed is demonstrated in SrAl(12)O(19):Pr,Cr using synchrotron radiation as one of the excitation sources. Upon VUV excitation of the 4f5d states of Pr(3+), quantum cutting could occur by a two-step energy transfer from Pr(3+) to Cr(3+) by cross relaxation and sequential transfer of the remaining excitation energy. A theoretical visible quantum efficiency of 147% is estimated in SrAl(12)O(19):2% Pr,5% Cr, suggesting the possibility of a VUV phosphor with visible quantum efficiency higher than 100% based on Pr(3+)-Cr(3+) pair in oxide materials.

Spectroscopic investigation of CaAl12O19:M3+ upon UV/vacuum–UV excitation: a comparison with SrAl12O19:M3+ (M = Pr,Cr)

In order to evaluate the possibility of using Cr³⁺ co-doping to modify the emission properties of Pr³⁺-based quantum cutting phosphors, which emit one ultraviolet (UV) and one visible photon from each vacuum-UV photon absorbed, into phosphors that emit two visible photons, the optical spectroscopies between 150 and 750 nm of CaAl₁₂O₁₉:M³⁺ (M = Pr,Cr) were investigated and compared with those of SrAl₁₂O₁₉:M³⁺ using synchrotron radiation as one of the excitation sources. When Pr³⁺ is excited to its 4f5d states, cascade emission of UV photons from the ¹S₀ state followed by visible photons from the ³P₀ state are both observed in (Ca,Sr)Al₁₂O₁₉:Pr³⁺. Similar to SrAl₁₂O₁₉:M³⁺, there exist desirable spectral overlaps between Pr³⁺ ¹S₀ emissions and the Cr³⁺ higher multiplet absorptions in CaAl₁₂O₁₉, which should be favourable to the energy transfer from Pr³⁺ ¹S₀ to Cr³⁺, converting the UV photon from Pr³⁺ ¹S₀ into the red Cr³⁺ emission. However, the host absorption band and the Cr³⁺-related charge transfer band have an unfavourable overlap with the Pr³⁺ 4f5d states in the vacuum-UV region, preventing efficient selective Pr³⁺ excitation under radiation of Xe discharge, a prerequisite for the quantum cutting process.

Experimental demonstration of the relationship between the OH− content and photoluminescence in Tb-doped YPO4∙2H2O

Tb-doped YPO4∙2H2O was synthesized via a simple wet-chemical route. Both the crystallinity of samples and the concentration of OH− adsorbed at the surface were experimentally controlled by adjusting the reaction time. An abnormal phenomenon that photoluminescence efficiency decreases with the increase of crystallinity demonstrates enormously adverse effect of OH− on photoluminescence, especially, as the OH− content reaches a critical value, the luminescent efficiency decreases more drastically. This strong dependence of photoluminescence on the OH− content indicates that to control the OH− content in a limited range or to reduce the OH− effect as much as possible is an efficient way to improve photoluminescence efficiency.