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. A Mn4+ singly-doped CLTO phosphor (CLTO:0.004Mn(4+)) showed a bright deep red-light emission corresponding to a narrow band around 707 nm (14144 cm(-1)) due to a Mn4+ E-2(g) -> (4)A(2g) spin-forbidden transition upon 365 nm UV excitation, which largely overlapped the absorption spectrum of plant phytochrome P-fr. The excitation spectrum (lambda(em) = 707 nm) presented a broad band ranging from 250 nm (40 000 cm(-1)) to 600 nm (16 667 cm(-1)), which can be decomposed into four Gaussian bands peaking at 318 nm (31 431 cm(-1)), 355 nm (28 148 cm(-1)), 410 nm (24 385 cm(-1)), and 476 nm (20 992 cm(-1)), corresponding to a Mn4+-O2- charge transfer (CT) transition, and Mn4+ transitions T-4(1g) <- (4)A(2g), T-2(2g) <- (4)A(2g) and T-4(2g) <- (4)A(2g), 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: 0.004Mn(4+) and CLTO:0.004Mn(4+), 0.04Nd(3+), 0.20Yb(3+) 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.
