Eu3+ multicenter formation and luminescent properties of Ca3Sc2Si3O12:Eu and Ca2YScMgSiO12:Eu single crystalline films

The work is dedicated to the investigation of Eu3+ multicenter formation and luminescent properties of Ca3Sc2Si3O12:Eu (CSSG:Eu) and Ca2YScMgSiO12:Eu (CYMSSG:Eu) single crystalline film (SCF) phosphors, grown by liquid phase epitaxy method onto Gd3Ga2.5Al2.5O12 (GAGG) and Y3Al5O12 (YAG) substrates, respectively. We have found notable differences in the luminescent properties of CSSG:Eu and CYMSSG:Eu SCFs caused by the Eu3+ multicenter formation in both garnets due to the different local surrounding of Eu3+ ions in the dodecahedral positions by the non-isovalent Sc3+/Mg2+ and Si4+ cations in the octahedral and tetrahedral positions of garnet hosts, respectively. A feature of the Eu3+ center creation in CYMSSG:Eu garnet in comparison with CSSG:Eu counterpart is the possibility of localization of Eu3+ ions in dodecahedral sites of both Ca2+ and Y3+ cations. However, based on the obtained results, we have presupposed preferable localization of the Eu3+ ions mainly in the Y3+ positions of this garnet

Luminescence of Ce3+ multicenters in Ca2+ -Mg2+ -Si4+ based garnet phosphors

Comparison of the luminescent properties of Ca3Sc2Si3O12: Ce and Ca2YMgScSi3O12: Ce single crystalline films (SCF) phosphors, grown by the liquid phase epitaxy method, was performed in this work. We have observed formation of the Ce3+ multicenters in Ca3Sc2Si3O12: Ce and Ca2YMgScSi3O12: Ce in the emission and excitation spectra as well as in the decay kinetics of the Ce3+ luminescence in SCFs of these garnets. Such Ce3+ multicenters possess different crystal field strength due to the inhomogeneous local surroundings of the dodecahedral positions of garnet host at the substitution of the octahedral positions by hetero-valence Mg2+ and Sc3+ ions and the tetrahedral positions by Si4+ ions. We confirm the presence of an effective energy transfer between different Ce3+ multicenters in Ce3+ doped Ca3Sc2Si3O12 and Ca2YMgScSi3O12 garnets. The positive trends in variations of the spectroscopic properties of the Ca2YMgScSi3O12: Ce garnet with respect to Ca3Sc2Si3O12: Ce garnet were observed also due to substitution of the dodecahedral sites of the garnet host by Y3+ ions and the octahedral sites by Mg2+ ions, which can be suitable for the development of new converters of white LEDs. Namely, due to the Y3+-Mg2+ doping, the luminescence spectrum of Ce3+ ions in Ca2YMgScSi3O12: Ce SCFs significantly extends in the red range in comparison with the Ca3Sc2Si3O12: Ce SCF counterpart

Luminescent and scintillation properties of Ce3+ doped Ca2RMgScSi3O12 (R = Y, Lu) single crystalline films

The work is dedicated to the growth and investigation of the luminescent and scintillation properties of single crystalline films (SCFs) of Ca2-xR1+xMg1+xSc1-xSi3O12:Ce (R = Y, Lu) mixed garnets with x = 0-0.25, grown using the liquid phase epitaxy method onto Y3Al5O12 substrates from PbO-B2O3 based flux. The absorption, luminescent and scintillation properties of Ca2-xY1+xMg1+xSc1-xSi3O12:Ce and Ca2-xLu1+xMg1+xSc1-xSi3O12:Ce SCFs with x = 0 and 0.25 were investigated and compared with the reference YAG:Ce and LuAG:Ce SCFs. Using the Ca2+, Mg2+ and Si4+ alloying, the Ce3+ emission spectra in Ca2-xR1+xMg1+xSc1-xSi3O12:Ce (R = Y, Lu; x = 0-0.25) SCFs can be notably extended in the red range in comparison with YAG: Ce and LuAG: Ce SCFs due to the increase of crystal field strength and Ce3+ multicenter creation in the dodecahedral positions of the lattices of these mixed garnet compounds. Due to the formation of Ce4+ ions, the as-grown Ca2-xR1+xMg1+xSc1-xSi3O12:Ce (R = Y, Lu) SCFs at x = 0 and 0.25 show relatively low light yield. However, after annealing in reducing atmosphere (95% N-2 + 5% H-2) at T > 1000 degrees C, a recharging Ce4+ -> Ce3+ takes place. After that, these SCFs possess the light yield about of 30% and 31% in comparison with the reference YAG: Ce and LuAG: Ce SCFs, respectively, and a fast scintillation response with the decay times in the ns range under a-particles excitation by Pu-239 (5.15 MeV) source

Study of the luminescence of Eu2+Eu^{2+} and Eu3+Eu^{3+} states in Ca3Ga2Ge3O12:EuCa_3Ga_2Ge_3O_{12}:Eu garnet using synchrotron radiation excitation

The work is dedicated to the investigation of $Eu^{2+}$ and $Eu^{3+}$ luminescence centers in the $Ca_3Ga_2Ge_3O_{12}$ garnet using synchrotron radiation excitation. The luminescence of $Eu^{2+}$ and $Eu^{3+}$ states was observed in the emission spectra of $Ca_3Ga_2Ge_3O_{12}$:Eu ceramics under excitation with energies in the exciton range and the range above band gap of this garnet. The luminescence of $Eu^{2+}$ ions $Ca_3Ga_2Ge_3O_{12}$ host is observed in the band peaked at 450–460 nm with decay time in the ten ns range and excited in the two wide bands peaked at 5.04 and 6.05 eV, related to the allowed 4f-5d transitions of $Eu^{2+}$ ions. The $Eu^{3+}$ luminescence can be excited via the $Eu^{2+}$ luminescence. We have also found the energies of formation of excitons bound with $Eu^{2+}$ and $Eu^{3+}$ ions in Ca3Ga2Ge3O12, being equal to 7.64 and 6.95 eV, respectively, and the onset of interband transitions in this garnet which is equal to 7.83 eV at 8 K. Strong increase of the luminescence intensity of $Eu^{2+}$ and $Eu^{3+}$ centers is observed under excitation above 21 eV due to multiplication of electronic excitation in $Ca_3Ga_2Ge_3O_{12}$ host

Comparison of the Luminescent Properties of Y3Al5O12:Pr\mathrm{Y_{3}Al_{5}O_{12}:Pr} Crystals and Films

The work is dedicated to comparative investigation of the luminescent properties of $\mathrm{Y_{3}Al_{5}O_{12}:Pr}$ (YAG:Pr)single crystals and single crystalline films using excitation by synchrotron radiation with an energy of 3.7–25 eV in the exciton range of YAG host. We have found that the differences in the excitation spectra and luminescence decay kinetics of YAG:Pr crystals and films are caused by involving the Y$_{Al}$ antisite defects and oxygen vacancies in the crystals and Pb$^{2+}$ flux related dopants in the films in the excitation processes of the Pr$^{3+}$ luminescence. Taking into account these differences, we have determined in more detail the energy structure of the Pr$^{3+}$ ions in YAG host and estimated the differences in the energies of creation of the excitons bound with the isolated Pr$^{3+}$ions in YAG:Pr films and the dipole Pr–Y$_{Al}$ antisite defect centers in the crystal counterpart