Quantum tripling in Tm 3+ doped La 2 BaZnO 5 phosphors for efficiency enhancement of small band gap solar cells

Energy Transfer Dynamics and Quantum Yield Derivation of the Tm3+ Concentration-Dependent, Three-Photon Near-Infrared Quantum Cutting in La2BaZnO5

“…The broad emission band at 750–850 nm (Figure a; upon 465 nm excitation) comprises a sharp peak at 784 nm and a broad shoulder at 800 nm, which notably originates from the 1 G 4 → 3 H 5 (energy gap approximately 12740 cm –1 ) and 3 H 4 → 3 H 6 (energy gap approximately 12500 cm –1 ) of Tm 3+ , respectively. , Decay curves of 651, 784, and 798 nm for the sample doped with lower x = 0.0005 Tm 3+ are depicted in Figure b, where the 651 and 798 nm decay curves were well fitted to a monoexponential function with a lifetime of approximately 244 and 588 μs, respectively, and the 784 nm curve was fitted by a nonexponential decay with a calculated lifetime of 315 μs (decay components τ 1 approximately 246 μs, τ 2 approximately 697 μs). These results suggest that emission at 800 nm is purely from the 3 H 4 state, but that at approximately 784 nm primarily from the 1 G 4 state of Tm 3+ .…”

“…However, once the Tm 3+ content exceeds the CQ threshold of 3 H 4 state, for example, x ≥ 0.01 in La 2– x Tm x BaZnO 5 , the CR of 3 H 4 → 3 F 4 + 3 H 6 → 3 F 4 (CR2) becomes rather efficient . Energy in the populated 3 H 4 state would be de-excited into the 3 F 4 state, thereby greatly decreasing the NIR emission at 1480 nm from the 3 H 4 state, but increasing the emission at 1800 nm from the 3 F 4 state (NIR emission spectra in Figure ).…”

“…The diffraction pattern was similar for each sample, corresponding to pure phase La 2 BaZnO 5 (JCPDS Card No. 80–1882) . Steady photoluminescence spectra were measured using an Edinburgh FLS920 spectrofluorimeter equipped with a continuous wave 450 W xenon lamp excitation source, a Hamamatsu R928 photomultiplier tube (PMT) for photon detection in 470–850 nm, and a liquid-nitrogen-cooled R5509–72 NIR PMT for 800–1650 nm.…”

“…In addition, the development of NIR QC in recent years promises to greatly enhance the efficiency of solar cells. − Theoretically, an ideal QC layer with emission at 1000 nm can increase the efficiency of Si solar cells up to approximately 40%, , which is much greater than its approximately 15% practical efficiency and even exceeds the Shockley-Queisser efficiency limit of approximately 30%. In addition to the extensive studies on RE 3+ /Yb 3+ (RE = Tb, Pr, Tm, Er, and Nd) codoping as a promising QC layer for Si solar cells, ,,− the multiphoton NIR luminescence of RE 3+ (RE = Dy, Ho, Tm, and Er) single doping system is spectroscopically demonstrated through energy transfer (ET) mechanisms of multistep cascade radiation and cross-relaxation (CR), thereby enhancing the photoresponse of Ge solar cells. − …”

“…La 2 BaZnO 5 was chosen as an ideal host because its shorter RE–RE (La–La) distance of approximately 3.4 Å (even less than that of β-NaYF 4 , approximately 3.5 Å, YVO 4 approximately 3.9 Å and YAG approximately 3.7 Å) enables efficient CR at higher Tm 3+ concentration . La 2 BaZnO 5 host lattice has a lower ℏω max (maximum phonon energy) of approximately 600 cm –1 (ℏω max of β-NaYF 4 approximately 450 cm –1 , YVO 4 approximately 900 cm –1 , and YAG approximately 700 cm –1 ) to benefit the efficient NIR emission of Tm 3+ . , Besides, Jaffrès et al enlighteningly discussed that, originating from blue-excited 1 G 4 state of Tm 3+ , several nearly resonant cross-relaxation ET just proceed to achieve the efficient NIR emission at about 1800 nm in theory . Furthermore, we primarily investigated the ET dynamics as a function of the Tm 3+ concentration in La 2 BaZnO 5 in spectroscopic experiments.…”