Simultaneous coloration erasure and significant photoluminescence enhancement via vacuum re-annealing in lanthanide-doped transparent ceramics

Defect Regulation of Terbium-Doped Y2Zr2O7 Transparent Ceramic for Wide-Range Multimode Tunable Light-Shielding Windows

“…Encouragingly, in our recent report, we found that with the generation of defect clusters [Ln Y 4+ –O 2– –Ln Y 4+ ] and [Ln Y 4+ –e • ] during the air-annealing treatment, the UV absorption edge of air-annealed terbium- (Tb-) or praseodymium- (Pr-) doped yttrium zirconate (Y 2 Zr 2 O 7 , denoted as YZO) ceramics showed a strong redshift. Inspired by that result, herein, we novelly developed Tb single doped YZO highly transparent ceramics for wide-range tunable light-shielding applications.…”

“…This phenomenon is associated with the fact that the YZO ceramic was sintered in the vacuum anoxic environment, and thus, some oxygen vacancies (V o ̈ ) and free electrons (e′) will be generated owing to the oxygen partial difference between the ceramic and the sintering furnace [see eq ]. Furthermore, these vacant oxygen sites trap one or two free electrons, generating some F + and F defect centers that capture some photons, resulting in the relatively low transparency of the YZO ceramic. ,− After doping with Tb, some tetravalent Tb ions will capture one electron to become trivalent state [see eq ], thereby, reducing the concentration of F + and F defect centers and improving the in-line transmittance of vacuum sintered YZO:Tb ceramics. The transmittance at 760 nm is 70%, 69%, and 68%, respectively, corresponding to YZO:0.2Tb, YZO:1Tb, and YZO:2Tb ceramics, respectively. …”

“…Moreover, the materials containing tetravalent Tb ions may be off-white in color, owing to the low-energy charge-transfer absorption of tetravalent ions . Therefore, the effect of annealing temperature on the redshift of optical absorption edge should be ascribed to the defect clusters arising from the air annealing process . During the annealing process, oxygen atoms existing in air can diffuse into the ceramics body, which will reduce the concentration of oxygen vacancies originating from the vacuum anoxic sintering process [see eq ].…”

“…Meanwhile, some of the doped Tb 3+ can lose an electron to become Tb 4+ during the air annealing treatment at high temperature, which is confirmed by the XPS spectra shown in Figure e (see Figure S5 of the Supporting Information), where the characteristic peak area of Tb 4+ (at around 1240 and 1275 eV) is significantly increased after annealing at 1300 °C. Two Tb 4+ replacing two Tb 3+ tend to produce one extra interstitial O 2– ion [see Equation ], and the negatively charged e • may be formed through the vacant oxygen sites occupied by free electrons, which promote the generation of [Tb Y 4+ –O 2– –Tb Y 4+ ] and [Tb Y 4+ –e • ] defect clusters due to the electrostatic interactions between the Tb 4+ ions and O 2– and e • . , The corresponding defect equilibriums we described could be expressed as …”

“…38 Therefore, the effect of annealing temperature on the redshift of optical absorption edge should be ascribed to the defect clusters arising from the air annealing process. 23 During the annealing process, oxygen atoms existing in air can diffuse into the ceramics body, which will reduce the concentration of oxygen vacancies originating from the vacuum anoxic sintering process [see eq 9]. 32 Meanwhile, some of the doped Tb 3+ can lose an electron to become Tb 4+ during the air annealing treatment at high temperature, which is confirmed by the XPS spectra shown in Figure 3e (see Figure S5 of the Supporting Information), where the characteristic peak area of Tb 4+ (at around 1240 and 1275 eV 39 ) is significantly increased after annealing at 1300 °C.…”