Ca3La2Te2O12:Mn4+ ,Nd3+ ,Yb3+ : an efficient thermally-stable UV/visible-far red/NIR broadband spectral converter for c-Si solar cells and plant-growth LEDs

摘要

A series of novel Mn4+,Nd3+,Yb3+-doped Ca3La2Te2O12 (CLTO) phosphors were prepared by substituting Te6+ for W6+ in the Ca3La2W2O12 compound using a high-temperature solid-state reaction method. AMn4+ singly-doped CLTO phosphor (CLTO:0.004Mn4+) showed a bright deep red-light emission corresponding to a narrow band around 707 nm (14 144 cm1 ) due to a Mn4+ 2 Eg - 4 A2g spin-forbidden transition upon 365 nm UV excitation, which largely overlapped the absorption spectrum of plant phytochrome Pfr. The excitation spectrum (lem = 707 nm) presented a broad band ranging from 250 nm (40 000 cm1 ) to 600 nm (16 667 cm1 ), which can be decomposed into four Gaussian bands peaking at 318 nm (31 431 cm1 ), 355 nm (28 148 cm1 ), 410 nm (24 385 cm1 ), and 476 nm (20 992 cm1 ), corresponding to a Mn4+-O2 charge transfer (CT) transition, and Mn4+ transitions 4 T1g ’ 4 A2g, 2 T2g ’ 4 A2g and 4 T2g ’ 4 A2g, respectively. Moreover, three kinds of Mn4+ emission sites were analyzed with the assistance of time-resolved spectra. With the single incorporation of Nd3+/Yb3+ into CLTO:Mn4+, energy transfer phenomena from Mn4+ to Nd3+/Yb3+ ions can be observed, which proceeded via non-radiative resonant and phonon-assisted mechanisms, respectively, resulting in the broadband spectral conversion of the UV/blue to NIR light. When Nd3+ and Yb3+ were co-doped into CLTO:Mn4+ to form the tri-doped CLTO phosphors, a successive energy transfer process, Mn4+ - Nd3+ - Yb3+, was determined based on the simultaneous energy transfer processes Mn4+ - Nd3+ and Nd3+ - Yb3+ in the co-doped samples, further enhancing the broadband spectral conversion process of the UV/blue to NIR region, which can be absorbed by photosynthetic bacteria and show high response when applied to c-Si solar cells. More attractively, the luminescence thermal stabilities of both CLTO:0.004Mn4+ and CLTO:0.004Mn4+,0.04Nd3+,0.20Yb3+ showed excellent performance, and the temperature-dependent luminescence properties of the Mn4+,Nd3+,Yb3+ tri-doped materials have been investigated for the first time. These results indicate that this kind of phosphor can be potentially applied to improving spectral conversion efficiency for c-Si solar cells and plant-growth far-red/NIR LEDs. In addition, this report provides a strategy wherein hosts for Mn4+ doping can be well enriched by substituting Te6+ for W6+ in certain tungstate compounds, which is highly desired in searching for novel red-emitting phosphors.