Enhancement of Mechanoluminescence in CaAl[sub 2]Si[sub 2]O[sub 8]:Eu[sup 2+] by Partial Sr[sup 2+] Substitution for Ca[sup 2+]

Abstract

Mechanoluminescence ͑ML͒ in a CaAl 2 Si 2 O 8 :Eu 2+ phosphor was greatly enhanced by partial Sr 2+ substitution for Ca 2+ ; ML intensity reached a maximum at Sr 2+ content of 40 mol %. Moreover, ML was not observed at Sr 2+ content of 80 mol % or higher. To investigate the relationship between ML and the crystal structure, Rietveld refinement of the crystal structures was performed, the results of which suggest that the observed ML enhancement and quenching phenomenon were associated with changes in the crystal lattice and crystal symmetry. Furthermore, the effects of partial Sr 2+ substitution on the structure and photoluminescence characteristics were also investigated, and the emission peak was blueshifted from 428 to 403 nm due to the decrease in the crystal field intensity around Eu 2+ . Based on electroluminescence measurements and the structural properties of the material, a possible mechanism for the enhancement in ML intensity is proposed.Mechanoluminescence ͑ML͒ is an intriguing luminescence phenomenon in which light emission is induced by various mechanical stimuli such as compression, friction, impact, and fracture. 1 The ML phenomenon has been known since the 16th century when it was discovered that crystalline sugar and certain minerals emit light when crushed. A considerable amount of research has focused on the fundamental features of the ML phenomenon. However, practical applications were not investigated until a decade ago, as ML was considered to be a fracture phenomenon and thus only a one-off event.The recently developed ML material SrAl 2 O 4 :Eu 2+ , which exhibits a strong green emission that can be repeatedly induced by weak elastic deformation, was developed by Xu and co-workers a decade ago. 2 This type of ML material has attracted considerable attention due to its potential applications as a stress sensor 3 and excitation source, 4 and many researchers have investigated these new ML materials.To date, several materials exhibiting ML in the elastic deformation region have been successfully developed, including SrAl 2 O 4 :Eu 2+ ͑green͒, 2 ZnS:Mn 2+ ͑yellow͒, 5 and BaTiO 3 -CaTiO 3 :Pr 3+ ͑red͒. 6 Although these phosphors exhibit a strong ML intensity, their luminescence spectra are limited to long wavelengths from green to red. For use as an excitation source, ML materials with a short-wavelength emission are highly desirable for many practical applications. Furthermore, these ML materials still have several problems, for example, the poor water resistance of SrAl 2 O 4 :Eu 2+ and the poor stability of ZnS:Mn 2+ and BaTiO 3 -CaTiO 3 :Pr 3+ . Therefore, it is essential to develop novel ML materials with a short-wavelength emission and superior stability. CaAl 2 Si 2 O 8 :Eu 2+ , which was successfully developed in our most recent studies, 7,8 satisfies both requirements because the material has a short-wavelength emission peak of 428 nm and exhibits superior stability to water. However, the ML intensity of CaAl 2 Si 2 O 8 :Eu 2+ is insufficient for practical use. The purpose of the pr...

Blue excited photoluminescence of Pr doped CaBi2Ta2O9 based ferroelectrics

“…The reasons for the enhancement of the PL intensity can be ascribe to the change of the lattice symmetry. The change of the lattice symmetry will give rise to a remarkable effect on the properties of Pr 3+ and further influence the luminescence properties [31][32][33][34], when Ca 2+ (1.34Å, 12 CN) ions are replaced by bigger radius Sr 2+ ions (1.44Å, 12 CN), the symmetry of the pseudoperovskite units was changed [33]. As previously discussed Pr 3+ ions dispersed in the pseudo-perovskite units of samples' crystal structure.…”

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

“…Previously, we have proposed that ML is attributed to local piezoelectric effect induced by lattice deformation, which strongly depend on the change of crystal symmetry and crystal lattice. 8 We speculate that the local piezoelectricity appeared in Sr 2 SnO 4 :Sm 3þ and Sr 3 Sn 2 O 7 :Sm 3þ and its strength is enhanced depending on the intra-layer structure, resulting in that the ML intensity is enhanced.…”

“…3 ML is a phenomenon where photons are emitted by mechanical stimuli; it is of particular interest for use in stress sensing devices which detect damage, fracture, and deformation in various structures. [4][5][6] Although some inorganic oxides, such as SrAl 2 O 4 :Eu 2þ , 7 CaAl 2 Si 2 O 8 :Eu 2þ , 8 SrMg 2 (PO 4 ) 2 :Eu 2þ , 9 display ML, perovskite oxides which exhibit intense ML are very attractive because they can be used as multi-functional materials. However, not all of the phosphors with perovskite structure have ML performance, for example, there is no ML in CaTiO 3 :Pr 3þ and BaTiO 3 :Pr 3þ .…”

Mechanoluminescence in (Sr,Ca,Ba) 2 SnO 4 :Sm 3+ ,La 3+ ceramics

“…Still, drawbacks like high cost and dissolution in water restrict the extent and depth of application to a certain degree. Up to now, existing ML materials are mostly long-lasting phosphors, such as SrAl 2 O 4 :Eu [4], BaSi 2 O 2 N 2 :Eu [10], CaAl 2 Si 2 O 8 :Eu [11], (Ca,Ba)TiO 3 :Pr [12] etc. Stannate phosphors as promising long-lasting phosphors demonstrated physical and chemical stability and more convenient synthesis process [13,14], some of which, such as Sr 2 SnO 4 :Sm 3þ , showed EML property though it is poor.…”

“…Stannate phosphors as promising long-lasting phosphors demonstrated physical and chemical stability and more convenient synthesis process [13,14], some of which, such as Sr 2 SnO 4 :Sm 3þ , showed EML property though it is poor. For an exact ML material, ML intensity could be enhanced by means of co-doping with suitable rare earth ions, like SrAl 2 O 4 : Eu, Dy better than SrAl 2 O 4 : Eu [7], or substituting partially ions of the host with other ions like (Sr,Ca)Al 2 Si 2 O 8 :Eu better than CaAl 2 Si 2 O 8 :Eu [11]. In the present work, by partially substituting Sr with Ca and Ba and co-doping with La in Sr 2 SnO 4 :Sm, we obtain (Sr 0.7 Ca 0.27 Ba 0.03 ) 1.92 SnO 4 Sm 0.02 La 0.06 with better ML performance.…”