Role of Ti4+ in the luminescence process of Al2O3:Si,Ti

Effects of pH and calcination temperature on structural and optical properties of alumina nanoparticles

“…PLE spectra (Fig.12.a) show that the 373 nm (3.32 eV) emission band has three absorption bands centered at 348 nm (3.56 eV), 250 nm (4.96 eV) and slightly below 200 nm (6.2 eV). The 348 nm (3.56 eV) and 250 nm (4.96 eV) absorption bands correspond tointra system and outran-system transitions in F 2 + centers respectively [17,18,[20][21][22]. It is demonstrated that a 5 eV photo excitation energy can dissociate electrons from F 2 and F 2 + centers and release them in the conduction band [20].…”

“…Nano alumina is different from the bulk, which cannot be considered as insulating, but as a new phase with different properties [9][10][11]. There have been many attempts to modifysemiconductor materials to produce highly luminescent materials.Also, nano alumina can be a good candidate for luminance materials because of the precence of some luminescent centers such as; OH-related radiative centers [14,15], nonbridging oxygen hole centers, oxygen vacancies (F + , F, F 2 2+ and F 2 centers) [16][17][18][19][20][21][22], V-type centers [23], the electron/hole traps produced by the defects, and other impurity defects (usually alumina samples contain the uncontrolled impurities of Cr, Fe and Ti ions) [15,[24][25][26][27][28][29][30][31][32][33][34]. The alumina nanoparticles also have excellent luminescent properties not found in bulk materials.…”

“…The peak strength of the strong blue emission depends on the atmosphere and annealing temperature.With increasing calcination temperatures up to 750 o C it the streng decreases and then from 750to 950 o C progressively increased. Some authors attribute it F + centers[69][70][71] while, most studies note that F + centers have an emission band at about 326nm[16][17][18][19][20][21][22]68].We suppose thatcomplex centers [Al i + F] are responsible of this emission band, because it manifests itself in another way.As the calcination temperature is increased up to 750 0 C (correspond to decreases in tetragonal distortion) it decreases and then with increasing calcination temperature from 750 to 950 0 C (correspond to increase in tetragonal distortion ) it increases. It is supposed that the new emission band depends on tetragonal distortion.…”

Studies of concentration dependences in the luminescence of Ti-doped Al2O3

“…Since the blue emission of Ti 4þ ions is a characteristic emission of wide-gap hosts 7,8 stimulated through charge-transfer transitions, the corresponding assignment of the 420 nm (3 eV) luminescence band of sapphire has been the subject of many publications since the end of the last century. 1,3,4,[9][10][11][12][13][14] Another hypothesis attributes this band to the emission of F þ or F defect centers (an oxygen vacancy occupied by one or two electrons, respectively) ever-present in aluminum oxide. [15][16][17] The existing ambiguity in the assignment of this luminescence has been acknowledged 2,18 and it has been suggested that there are several clear features permitting to discriminate between the impurity and defect emission, such as band half-width, excitation spectra, lifetimes etc.…”

The Development and Progression of Micro-Nano Optics

“…Micro-nano luminescent materials mainly use micro-nano particles as a luminescent matrix, including pure and doped micro-nano semiconductor luminescent materials, rare earth ions and excessive metal ions doped nano-oxides, sulfides, composite oxides, and a variety of micro-nano inorganic salt luminescent materials. For activator materials, there are usually two types of ions: a class of transition metal ions, such as Mn 4+ /Mn 2+ ( Huang et al, 2016a ), Ti 4+ ( Page et al, 2010 ), Cr 3+ ( Chen et al, 2014 ), Cd 2+ ( Mall and Kumar, 2010 ), etc. ; the second group is rare earth metal ions Eu 3+ /Eu 2+ , and Tb 3+ , Pr 3+ , etc.…”