2022
DOI: 10.1002/adfm.202113065
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Upconversion Nanocrystals with High Lanthanide Content: Luminescence Loss by Energy Migration versus Luminescence Enhancement by Increased NIR Absorption

Abstract: Lanthanide-doped upconversion nanoparticles (UCNPs) have attracted a lot of interest due to their benefits in biological applications: They are not suffering from intermittence and provide nearly background-free luminescence. The progress in synthesis nowadays enables access to complex core-shell particles of controlled size and composition. Nevertheless, the frequently used doping ratio dates back to where mostly core-only particles of relatively large size have been studied. Especially at low power excitatio… Show more

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Cited by 46 publications
(28 citation statements)
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“…For nanoparticles upon excitation, the ground-state Er 3+ was generally pumped to the high-lying 4 F 7/2 level via sequential ground-state absorption (GSA) and excited-state absorption (ESA) processes and energy transfer process from the neighboring high-lying Yb 3+ in the case of Yb 3+ -contained nanoparticles . The subsequent multiphonon relaxation (MPR) processes that such high-lying Er 3+ species underwent typically led to the population of green ( 2 H 11/2 and 4 S 3/2 ) and red ( 4 F 9/2 ) emitting states with the former enabling emission bands centered at 525 and 540 nm ( 2 H 11/2 / 4 S 3/2 → 4 I 15/2 ), respectively, while the latter imparting red emission feature with wavelength around 650 nm ( 4 F 9/2 → 4 I 15/2 ). …”
Section: Resultsmentioning
confidence: 99%
“…For nanoparticles upon excitation, the ground-state Er 3+ was generally pumped to the high-lying 4 F 7/2 level via sequential ground-state absorption (GSA) and excited-state absorption (ESA) processes and energy transfer process from the neighboring high-lying Yb 3+ in the case of Yb 3+ -contained nanoparticles . The subsequent multiphonon relaxation (MPR) processes that such high-lying Er 3+ species underwent typically led to the population of green ( 2 H 11/2 and 4 S 3/2 ) and red ( 4 F 9/2 ) emitting states with the former enabling emission bands centered at 525 and 540 nm ( 2 H 11/2 / 4 S 3/2 → 4 I 15/2 ), respectively, while the latter imparting red emission feature with wavelength around 650 nm ( 4 F 9/2 → 4 I 15/2 ). …”
Section: Resultsmentioning
confidence: 99%
“…In general, loss of emission intensity for UCNPs occurs when raising the dopant concentration beyond a threshold value, which is known as concentration quenching effect. 27,28 To minimize the detrimental concentration quenching, UCNPs are typically doped with a relatively low concentration of Ln 3+ ions, leading to insufficient harvesting of excitation light and consequently weak emission. Encouragingly, recent advances have demonstrated the effective alleviation of energy loss at high dopant concentration through several complementary strategies, thereby making heavy Ln 3+ doping a feasible way to enhance the UCL of UCNPs.…”
Section: Chemical Composition Tuningmentioning
confidence: 99%
“…After decades of fast development, lanthanide‐doped upconversion luminescence (UCL) has been extensively studied in a wide range of areas from previous bioimaging, contactless temperature probing, and anticounterfeiting to nowadays compact lasing, optogenetics, single nanoparticle (NP) tracking, and X‐ray detection [1–12] . Obviously, a deep understanding of the working principles behind those individual applications is the key to successful modulation of UCL emission with expected parameters in terms of lifetime, relative intensity, and wavelength, toward different purposes [13–20] …”
Section: Introductionmentioning
confidence: 99%
“…[1][2][3][4][5][6][7][8][9][10][11][12] Obviously, a deep understanding of the working principles behind those individual applications is the key to successful modulation of UCL emission with expected parameters in terms of lifetime, relative intensity, and wavelength, toward different purposes. [13][14][15][16][17][18][19][20] Unfortunately, UCL process was empirically assumed to have the same time-resolved output profile as that of organic dye/quantum dot, [21][22][23][24] which works as one luminescing unit and is composed of a sharp rise and a steep decay edge originated from population and depopulation process, [25] respectively. In detail, electrons are pumped to excited state under proper excitation, and (after a quick relaxation) return immediately to the ground state accompanied with luminescence emission (Figure 1a).…”
Section: Introductionmentioning
confidence: 99%