Electron paramagnetic resonance and luminescent properties of Mn2+:MgGa2O4 phosphor

Abstract

Electron-paramagnetic-resonance ͑EPR͒ and photoluminescence ͑PL͒ studies on magnesium gallate ͑MgGa 2 O 4 ͒ phosphor activated with divalent manganese have been carried out. The EPR spectrum exhibits a six-line hyperfine structure centered at g = 1.995, which is a characteristic of a Mn 2+ ion with a nuclear spin I =5/2. The spin-Hamiltonian parameters have been evaluated. The concentration and temperature ͑123-433 K͒ dependences of EPR signals have been studied. The number of spins participating in resonance ͑N͒ with temperature obeys the Boltzman law and from the graph of log N versus 1 / T the activation energy has been evaluated. The paramagnetic susceptibilities ͑͒ have been calculated from the EPR data at different temperatures and it is interesting to note that it obeys the Curie-Weiss behavior. The Curie constant has been evaluated from the 1 / versus T graph. A bright green photoluminescence according to the transition 4 T 1 → 6 A 1 whose emission peak is located at 502 nm is observed from the phosphor under UV excitation when excited by 267-nm light. Such a stable luminescence performance is promising for use in the field of flat panel light-emitting devices. The mechanism involved in the generation of green emission has been explained in detail.

Synthesis and luminescent properties of magnesium gallate spinel doped with Mn2+ and Eu3+ ions

“…The 240 nm excitation band corresponds to band-to-band transitions and may indicate recombination mechanism of Mn 2+ ions excitation. Similar results were presented in [9,12] papers where X-ray excitation and thermo-stimulated luminescence technique were used. Excitation of manganese ions is presented by an intense broad band in the 230-280 nm spectral region that belongs to fundamental absorption region of spectra.…”

“…Inversion of spinel structure is caused by occupying octahedral sites with Mg 2+ cations and tetrahedral sites by Ga 3+ cathions due to close ionic radii [9]. Previously reported papers of different authors [2,10] determine that temperature range of spinel phase appearance is from 1100 to 1400 °C.…”

Effects of Cr3+ concentration on the optical properties of Cs2NaAlF6 single crystals

“…In the last years a growing interest in the development of new insulating materials doped with transition metals has been observed, leading these materials to be applied in a wide range of fields, for instance, as signal transmission [1], displays manufacturing [2], tunable solid state lasers at room temperature [3], optical sensors [4], electroluminescent and thermoluminescent devices [5,6], broadband amplifiers [7], radiation detectors [8], white-light emission sources [9,10] and many other areas. These compounds also present very interesting optical properties, such as emission in a wide spectrum with high quantum yield, broad absorption bands and high emission intensity.…”

Cr3+ impurity concentration and excitation dependences of magnesium gallate spinel photoluminescent data

“…In an inverted spinel, the B 3+ cations occupy tetrahedral sites, while A 2+ and B 3+ cations are randomly distributed on octahedral sites. The inversion degree of MgGa 2 O 4 depends on the synthesis temperature [25] with the Mg 2+ ions occupation ratio varying from 0.9 at 900 • C to 0.84 at 1400 • C [12].…”

“…The current research in light emitting materials is driven by their use in several technologically important applications [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. We can mention, among many others: (a) pipes of cathode rays, phosphor-covering screens that under ultraviolet radiation or electron beams emit visible light; (b) tunable lasers operating at room temperature; (c) special light bulbs, for example, fluorescence Hg lamps, that use metal vapors tubes covered by a fluorescent dye that absorbs the metal emission and emits white light; (d) electroluminescent devices like LED's, solid state semiconductors that usually emit red, yellow or green light, and RE-doped materials as RE 2 (WO4) 3 : Eu 3+ , Tm 3+ , Eu 2+ , Tb 3+ , Sm 3+ for applications as flat panel monitors; (e) scintillators, materials that absorb high energy electromagnetic radiation or charged particles and release the absorbed energy as photons.…”