Downconversion Quantum Efficiency Research Articles

Broadband near-infrared downconversion luminescence in Yb3+-doped BaZn2(BO3)2

BaZn2(BO3)2 self-activated phosphors were prepared by the conventional high temperature solid-state method. The PL spectra of BaZn2(BO3)2 powders prepared under reductive and air atmosphere consist of a weak ultraviolet emission band (∼410 nm) and a broad emission band which were centered at ∼ 500 and 545 nm, respectively. According to the spectral analysis and EPR results, the green and yellow emissions may arise from the transitions of photo-generated electron close to the conduction band to the deeply trapped hole in single ionized oxygen vacancy (V+ o) centers and single negatively charged interstitial oxygen ion (O- i), respectively. An efficient broadband near-infrared (NIR) quantum cutting was demonstrated in Yb3+ doped BaZn2(BO3)2 phosphor. Upon excitation with an ultraviolet photon at 375 nm, the emissions of two NIR photons at 983 nm from Yb3+ ions were achieved. The dependences of the visible and NIR emissions, the decay lifetime, the energy transfer efficiency, and the quantum efficiency on the Yb3+ doping content were investigated in detail. The results indicated that the maximum energy transfer and the corresponding downconversion quantum efficiency could reach between 68.5% and 168.5%.

Enhanced near-infrared quantum cutting in CaMoO4:Yb3+ phosphors induced by doping with Li+ ions for improving solar cells efficiency

The near-infrared (NIR) quantum cutting (QC) CaMoO4:Yb3+ phosphors co-doped with Li+ ions were synthesized by the sol–gel methods. The dependence of the structure, morphology, photoluminescence (PL) and downconversion (DC) quantum efficiency on the Li+ doping concentration have been investigated in details. It was demonstrated that the CaMoO4:Yb3+ phosphors with appropriate concentration of the Li+ ions show improved crystallinity and remarkable increase of the NIR emission from the Yb3+ ions, if compared with the Li+-free samples. The enhancement of the NIR emission and DC quantum efficiency was suggested to be a consequence of the improved crystallinity and stronger absorption of the host due to the [MoO4] tetrahedra distortion induced by the Li+ ions. Cooperative energy transfer (CET) from the host to the Yb3+ ions is discussed as a possible mechanism for the NIR emission enhancement. Excellent luminescence properties of the Li+ doped CaMoO4:Yb3+ phosphor demonstrate its potential application as a better QC layer to increase the energy conversion efficiency of the Si-based solar cells.

Near-infrared luminescence and energy transfer in CaMoO4: Ho3+, Yb3+ phosphor

Down-conversion (DC) is a promising avenue to break Shockley–Queisser detailed balance limit, and efficient DC from one ultraviolet visible photon to two near-infrared (NIR) photons is realized in the Ho3+–Yb3+ co-doped CaMoO4 system. The scheelite samples have been synthesized via solid-state reaction method. Upon blue light excitation (447 nm), Ho3+ transfers its energy to Yb3+ via resonant cross-relaxation process, bringing about NIR luminescence. The visible emissions decrease as a function of Yb3+ contents, while NIR emission at 996 nm first increases and then decreases due to CQ at Yb3+ contents beyond 15 mol %. The lifetime of Ho3+: 5F4, 5S2 → 5I8 with various Yb3+ contents is calculated as 114, 85, 73, 70, 64, 59 and 55 μs, respectively. The maximum energy transfer efficiency and the corresponding DC quantum efficiency are estimated to be 48 and 148 %. The phosphor may be a potential candidate for application in enhancing the performance of crystalline silicon solar cells.

Broadband near-infrared downconversion luminescence in Eu2+–Yb3+ codoped Ca9Y(PO4)7

An efficient broadband near-infrared (NIR) quantum cutting was demonstrated in Eu2+–Yb3+ codoped Ca9Y(PO4)7 phosphor. Upon excitation of Eu2+ ions to the 4f65d1 level with an ultraviolet photon at 322nm, emissions of two NIR photons at 983nm of Yb3+were achieved. The dependences of the visible and NIR emissions, the decay lifetime, the energy transfer efficiency (ETE), and the quantum efficiency (QE) on the Yb3+ doping content were investigated in detail. The results indicated that the maximum ETE and the corresponding downconversion QE can reach between 80% and 179%, respectively.

A Wafer‐Level Integrated White‐Light‐Emitting Diode Incorporating Colloidal Quantum Dots as a Nanocomposite Luminescent Material

High-brightness, color-tunable colloidal quantum dots are incorporated in 3D nanoporous GaN to create a nanocomposite material (CQD/NP-GaN), which is demonstrated to be an effective approach for a wavelength down-conversion nanomaterial in solid-state lighting. The white-light-emitting diode (LED) made from a blue GaN-based LED and the CQD/NP-GaN shows an increase of extraction efficiency by a factor of 2, a controllable white color, and a down-conversion quantum efficiency as high as 82%.

Broadband UV excitable near-infrared downconversion luminescence in Eu 2+/Yb 3+:CaF 2 nanocrystals embedded glass ceramics

Cooperative downconversion was realized in glass ceramics containing Eu 2+/Yb 3+:CaF 2 nanocrystals with Eu 2+ greatly absorbing ultraviolet photons. Upon excitation of Eu 2+ ions to the 5 d level with an ultraviolet photon at 320 nm, emission of two near infrared photons at 976 nm of Yb 3+ were achieved. The dependence of the visible and near-infrared emissions, decay lifetime, and quantum efficiency on the Yb 3+ doping content has been investigated. The maximum energy transfer efficiency and the corresponding downconversion quantum efficiency were estimated to be 51% and 151%, respectively.

Quantum cutting downconversion by cooperative energy transfer from Ce3+ to Yb3+ in borate glasses

Quantum cutting downconversion (DC) involving the emission of two near-infrared (NIR) photons for each ultraviolet (UV) photon absorbed is realized in the Ce3+/Yb3+ codoped borated glasses. Upon excitation of Ce3+ ion with an UV photon at 330 nm, Yb3+ ions emit two NIR photons at 976 nm through an efficient excitation of Ce3+:5d and subsequent cooperative energy transfer (ET) from Ce3+:5d to Yb3+:F25/2. The maximum ET efficiency and the corresponding DC quantum efficiency were estimated to be 74% and 174%, respectively.