Luminescence of excitons in single-crystal garnets

Single-crystalline films of Ce-doped YAG and LuAG phosphors: advantages over bulk crystals analogues

“…Unlike the SCF, the emission band of Y 3+ Al AD with l max ¼ 330 nm prevails in the luminescence spectra of YAG:Ce SC at 300 K ( Fig. 1, curve 2), which evidences the absence of AD in YAG:Ce SCF [18,21].…”

“…1 shows the UV emission spectra of YAG:Ce SC at 10 and 300 K (curves 1 and 2, respectively) at the excitation by SR with energies E ¼ 20 eV and 11.3 eV which exceed the energy gap of YAG E g ¼ 7:8 eV and correspond to the ''bottom'' and ''top'' of excitation spectra, respectively, in the region 8.0-25 eV of interband transition [22], in comparison with the analogous spectra for the SCF of this garnet (curves 3 and 4). The luminescence spectrum of the YAG:Ce SC at 10 K (curve 1) presents the superposition of the bands with l max ¼ 263 nm (4.71 eV) and 330 nm (3.87 eV) which are caused, correspondingly, by the emission of self-trapped excitons (STE) [21,23] and centers formed by the Y 3+ Al AD [18,[21][22]. In contrast to the SC, only the weak STE luminescence in the band with l max ¼ 260 nm (4.76 eV) occurs in the luminescence spectrum of the YAG:Ce SCF at 10 K (Fig.…”

“…5c, curve 1. At 10 K, the Ce 3+ ions luminescence in the YAG:Ce SC is mainly excited in the narrow band with E Ce ex ¼ 6:8 eV: This energy corresponds to the energy of creation of bound excitons whose wave function is strongly correlated with the activator [21]. For the YAG:Ce SC, it is typical that the spectral location of this maximum is close to the position of excitation peak of the Y 3+ Al AD luminescence (Fig.…”

“…On the contrary, it is shown that Y Al 3+ and Lu Al 3+ AD are not formed when using the lowtemperature method of crystallization [18,20]. Therefore, the SCF of garnets are also useful model objects for the investigation of the relaxation phenomena at low-energy excitation, in particular, the luminescence of excitons in multisublattice oxides [21,22]. Particularly, in the SCF it is possible to investigate the luminescence of excitons without the typical ''background'' emission of the centers formed by AD or vacancy-like defects which is always present in SC of these oxides.…”

“…However, in the single crystals (SC) of these garnets obtained by crystallization from the melt at significantly higher temperatures (1800-1900 1C) than at the LPE growth procedure (850-1100 1C), the concentration of AD reaches the value of 0.2-0.5 at% [20][21][22]. The Y Al 3+ and Lu Al 3+ AD as analogues of isoelectronic impurities create the centers of luminescence in UV region and trap centers [17,19].…”