Editors' Choice—Investigation of Luminescence and Photoacoustic Properties in Ce³⁺-DopedLn₃Al₅O₁₂(Ln= Lu, Y, Gd) Garnet

Abstract

Optical and photoacoustic properties of Ce 3+ -doped lanthanide (Lu, Y, Gd) aluminum garnet were investigated. In the photoacoustic (PA) spectra, the 5d 1 (lowest 5d level) band of Ce 3+ was observed at around 450 nm in the obtained Ce 3+ -doped garnet samples. This result shows that a part of the excited energy is converted to thermal energy, which is generated by some nonradiative processes. In Y 3 Al 5 O 12 :Ce 3+ , the 5d 1 PA peak wavelength is shorter than the 5d 1 photoluminescence excitation peak wavelength, which indicates that part of the heat generation is caused by the phonon relaxation process within 5d 1 state. The PA intensity and luminescence quantum efficiency of the Ce 3+ -doped gadolinium yttrium aluminum garnets ((Gd 0.5 Y 0.5 ) 3 Ce3+ -doped garnet materials have attracted a great deal of attention in w-LEDs and scintillators applications because of their intense broad absorption in a blue region, high quantum efficiency, and luminescence in various colors. These absorption and luminescence properties of the Ce 3+ ion are derived from the 4f-5d allowed transitions. The luminescence color variation is caused by the shift of 5d excited level by the nephelauxetic effect (centroid shift caused by covalency) and the crystal field splitting.1-4 The chemical formula of general garnet crystals can be expressed as {A} 3 [B] 2 (C) 3 O 12 , where {A}, [B] and (C) represent the cations at the dodecahedral, octahedral and tetrahedral sites, respectively. The dodecahedral site to which Ce 3+ occupies has the distorted square anti-prism structure with D 2 point-group symmetry, which results in the large crystal field splitting of 5d state. The split 5d levels are referred as 5d 1 , 5d 2 , 5d 3 . . . from the lowest 5d energy level. The crystal field strength and 5d splitting can be changed by varying the garnet component ions. So far, the optical properties of Ce 3+ in many garnet host compositions have been studied. [5][6][7][8][9][10][11][12][13][14] When the dodecahedral site in Ln 3 Al 5 O 12 are changed from the smaller lanthanide, Ln ion to the larger Ln ion, for instance in the order of Lu, Y, Tb to Gd, the 5d 1 energy shifts to the lower energy and quenching temperature becomes much lower. 15,16 Therefore, the luminescence quantum efficiency of Ce 3+ :5d 1 -4f at room temperature can be decreased with increasing ionic radius of the dodecahedral site. The decrease of quantum efficiency should cause excess heat generation through some nonradiative relaxation processes.Photoacoustic (PA) spectroscopy is one of the measurements to get information of heat generation after photon absorption. The heat flux generated by excitation light is transported in a sample and changes the surface temperature. As a result, the gas pressure in the photoacoustic chamber will be changed and the formed sound can be detected by a microphone. Grinberg et al. reported the PA spectrum of Y 3 Al 5 O 12 :Ce 3+ in a wide wavelength range between 265 nm and 570 nm and discussed the results with configuration coordinate diagram...

The Effect of Sr2+ on Luminescence of Ce3+-Doped (Ca,Sr)2Al2SiO7

“…Besides, the onset temperature of thermal quenching ( T 95% ) is estimated at 375 K for Ca 1.98 Ce 0.01 Na 0.01 Al 2 SiO 7 , and that at 310 K for Sr 1.98 Ce 0.01 Na 0.01 Al 2 SiO 7 . When we consider that quenching is mainly caused by thermal ionization of Ce 3+ 5d electrons to the conduction band (CB) as proposed in Ce 3+ -doped garnets, − Ln 2 O 3 (Ln = Y, Lu, La), Lu 2 SiO 5 , and GdAlO 3 , the activation energy Δ E of thermal quenching can be derived from the single-barrier quenching model, eq , where Γ­( T ) and Γ(0) denote the decay time at temperature T and 0 K, correspondingly, A is a pre-exponential factor indicating the rate constant for the thermally activated escape, and k is the Boltzmann constant [8.6173324(78) × 10 –5 eV/K]. The fitting curves are plotted as red lines in Figure .…”

Thermal ionization and thermally activated crossover quenching processes for5d−4fluminescence inY3AlUeda1, Meijerink2, Dorenbos3 et al. 2017Phys. Rev. BSelf Cite692420View full textAdd to dashboardCite

“…In the past, we have focused on the garnet materials doped with Ce 3+ for the analysis of the quenching mechanisms and for the development of persistent phosphors [14][15][16][17] (LuAG), precise configuration coordinate diagrams were constructed from low-temperature spectroscopy data and the 5d-4f thermal quenching behavior was related to the energy gap between the lowest 5d 1 state and the next lower 4f state [10]. On the basis of the good agreement between the configuration coordinate diagrams and the quenching temperature, the quenching process of the 5d-4f luminescence in these materials is attributed to the thermally activated crossover process [10] [18,20].…”

First-Principles Analysis of the Effects of Covalency and Ionicity on the 4f–5d Transition Energy of Ce3+ in Garnet-Type Oxides

“…39,40 The reduction of the degeneracy weighted average 5d level energy (barycenter) due to the covalency (nephelauxetic effect) corresponds to ε c . 32,[41][42][43] The ε cfs value decreases as the cation bond length increases, and the shape and size of the coordination polyhedron of Ce primarily determine the ε cfs value. 32,39,44 Typically, the ε cfs value follows a decreasing order of octahedral > cubic > dodecahedral coordinations.…”