Chao-Nan Xu

Strong elasticoluminescence from monoclinic-structure SrAl2O4

Elastico-deformation luminescence in strontium aluminates was investigated systematically using precisely controlled pure-phase Eu-doped strontium aluminates of SrAl12O19, Sr4Al14O25, SrAl4O7, α-SrAl2O4, β-SrAl2O4, Sr3Al2O6 and their mixed phases. This study revealed that only the α-SrAl2O4 phase produces strong elastico-deformation luminescence; other strontium aluminates show no deformation luminescence. Correlation of deformation luminescence and crystal structure was found. The α-SrAl2O4 has the lowest symmetry, crystallizing in a monoclinic structure. This finding can be applied in designing strong elastico-deformation-luminescent materials.

Influence of Eu, Dy co-doped strontium aluminate composition on mechanoluminescence intensity

Abstract We have investigated the mechanoluminescence (ML) of Eu,Dy co-doped strontium aluminates. The SrAl 2 O 4 and Sr 3 Al 2 O 6 indicate high ML intensity, which is clearly visible to the naked eye in the air. SrAl 2 O 4 :Eu,Dy shows the highest ML intensity and has many filled traps, high quantum efficiency and moderate stiffness. On the other hand, Sr 3 Al 2 O 6 :Eu,Dy does not have many filled traps and high relative quantum efficiency, but Sr 3 Al 2 O 6 :Eu,Dy shows relatively high ML intensity. Sr 3 Al 2 O 6 :Eu,Dy indicates low stiffness. SrAl 4 O 7 :Eu,Dy has many filled traps and high relative quantum efficiency, but SrAl 4 O 7 :Eu,Dy shows very small ml intensity. SrAl 4 O 7 :Eu,Dy indicates high stiffness. This suggests that the stiffness is an important factor for the ML intensity of the Eu,Dy co-doped strontium aluminate system.

Ultraviolet mechanoluminescence from SrAl2O4:Ce and SrAl2O4:Ce,Ho

Phosphors with ultraviolet (UV) mechanoluminescence (ML) SrAl2O4:Ce (SAOCe) and SrAl2O4:Ce,Ho (SAOHoCe) were reported in this letter. The results reveal that the ML emission band is located at 375nm similar to photoluminescent (PL) peak, which indicates that ML is emitted from the same center of Ce3+ ions as PL. Furthermore, the addition of Ho3+ increases the UV ML intensity of SAOHoCe (56nJ∕loadcycle) considerably [approximately two orders of magnitude greater than that of SAOCe (0.21nJ∕loadcycle)]. The formation of many shallow traps (Ho3+−e−) may be responsible for this enhancement.

Strong reddish-orange light emission from stress-activated Srn+1SnnO3n+1:Sm3+ (n=1, 2, ∞) with perovskite-related structures

We report mechanoluminescence (ML) in Sm3+-doped Srn+1SnnO3n+1 (n = 1, 2, ∞) phosphors with perovskite-related structures, which consist of layered units depending on the number of n. The intensity of the ML was strongly dependent on the layered structure; the ML intensity for Sr3Sn2O7:Sm3+ was three orders of magnitude higher than that for SrSnO3:Sm3+. The charge transfer state (CTS) band in the photoluminescence excitation spectra was observed for Sr3Sn2O7:Sm3+ and Sr2SnO4:Sm3+, indicating that the efficient energy transfers from the host to the Sm3+ ions. The formation of CTS and the layered structure may be responsible for this ML enhancement.

Blue Light Emission from Stress-Activated CaYAl3O7 : Eu

We have revealed that CaYAl 3 O 7 :Eu phosphor emits blue light under the application of mechanical stress, called mechanoluminescence (ML). The influences of sintering temperature on photoluminescence (PL) and ML were investigated in order to gain suitable synthesis conditions. The results revealed that the sample sintered at 1300°C shows strong PL and ML intensities, while further heating induces quenching of PL and ML. The ML and PL spectra are similar, which indicates that ML is emitted from the same center of Eu 2+ ions as PL. This blue ML emission can be observed by the naked eye when the sample sintered at 1300°C is compressed. Furthermore, the ML intensity of CaYAl 3 O 7 :Eu proportionally increased with the increase of mechanical load.

Intense visible light emission from stress-activated ZrO2:Ti

We have investigated the luminescence phenomena from stress-activated ZrO2:Ti. The luminescence is clearly visible to the naked eye in the atmosphere. The luminescence center has been identified as the Ti4+ ion from spectra of the mechanoluminescence and also from photoluminescence studies of ZrO2:Ti. The mechanoluminescence intensity decreases on repetitive application of stress but recovers completely on irradiation with ultraviolet light. ZrO2 is an n-type semiconductor and has electron traps. It is suggested that the mechanoluminescence mechanism arises from the movement of dislocations and recombination between electrons and holes released from these traps which are associated with the Ti4+ centers.

Stress-Induced Mechanoluminescence in SrCaMgSi2O7 : Eu

We have revealed that SrCaMgSi 2 O 7 :Eu phosphors emit blue-greenish light under the application of a mechanical stress, called mechanoluminescence (ML). The ML showed a similar spectrum to photoluminescence (PL), which indicated that ML is emitted from the same center of Eu 2+ ions as PL. Such a blue-greenish light of ML emission can be seen by the naked eye when pressing the sample. In addition, the ML intensity of SrCaMgSi 2 O 7 :Eu proportionally increased with the increase of mechanical load.

BLUE LIGHT EMISSION FROM STRESS-ACTIVATED SR2MGSI2O7:EU

We discovered that Sr2MgSi2O7:Eu phosphor emits blue light under the application of a mechanical stress, a phenomenon known as mechanoluminescence (ML). The ML showed a similar spectrum as photoluminescence (PL), which indicated that ML is emitted from the same center of Eu2+ ions as PL. The analysis of structure and thermoluminescne suggested that the origin of ML for Sr2MgSi2O7:Eu phosphor can be attributed to strain-induced electroluminescence, that is, piezoelectricity impelled the trapped electrons to escape from the trap and produce ML. Furthermore, the relation between ML intensity and compressive load is close to linearity, which indicate that this sample can be used for smart-skin and self-diagnosis applications.

Electroluminescent ceramics excited by low electrical field

Strong green-light emission occurs in Eu:SrAl2O4 ceramics and Eu:SrAl2O4/poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) composites when excited by a lower dc or ac voltage. That emission is caused by strong electric-mechanic-optic interaction. The composite shows stronger luminescent emission intensity in comparison to similar ceramics because of an enhanced piezoelectric effect from P(VDF-TrFE)—a typical piezoelectric polymer.

Visualization of stress distribution using mechanoluminescence from Sr3Al2O6: Eu and the nature of the luminescence mechanism

We have investigated the dependence of the mechanoluminescence intensity from Sr3Al2O6: Eu on compressive stress. The distribution of the mechanoluminescence intensity, which is clearly visible to the naked eye, is consistent with the calculated stress distribution. The luminescence centre has been identified as the Eu2+ ion from spectra of the mechanoluminescence and also from photoluminescence studies of Sr3Al2O6: Eu. The mechanoluminescence intensity decreases on repetitive application of stress but recovers completely on irradiation with ultraviolet light. The Sr3Al2O6: Eu is a p-type semiconductor and has hole traps of depth 0.11 eV. It is suggested that the mechanoluminescence mechanism arises from the movement of dislocations and recombination between electrons and holes released from these traps which are associated with Eu2+ centres.