Photonic Effects on the Radiative Decay Rate and Luminescence Quantum Yield of Doped Nanocrystals

Abstract

Nanocrystals (NCs) doped with luminescent ions form an emerging class of materials. In contrast to excitonic transitions in semiconductor NCs, the optical transitions are localized and not affected by quantum confinement. The radiative decay rates of the dopant emission in NCs are nevertheless different from their bulk analogues due to photonic effects, and also the luminescence quantum yield (QY, important for applications) is affected. In the past, different theoretical models have been proposed to describe the photonic effects for dopant emission in NCs, with little experimental validation. In this work we investigate the photonic effects on the radiative decay rate of luminescent doped NCs using 4 nm LaPO4 NCs doped with Ce(3+) or Tb(3+) ions in different refractive index solvents and bulk crystals. We demonstrate that the measured influence of the refractive index on the radiative decay rate of the Ce(3+) emission, having near unity QY, is in excellent agreement with the theoretical nanocrystal-cavity model. Furthermore, we show how the nanocrystal-cavity model can be used to quantify the nonunity QY of Tb(3+)-doped LaPO4 NCs and demonstrate that, as a general rule, the QY is higher in media with higher refractive index.

Quenching Pathways in NaYF4:Er3+,Yb3+ Upconversion Nanocrystals

“…In addition to inducing nonradiative quenching, the solvent—through its refractive index n —also affects the radiative decay rate Γ rad of dopant centers in NCs: 33,34 where Γ rad bulk is the radiative decay rate in a bulk sample, and n NC is the refractive index of the NC material [here, n NC = 1.48 (ref (39))]. This effect is the same for all luminescent centers inside a NC independent of their exact location, if the NC is (quasi-)spherical and much smaller than the emission wavelength.…”

“…e ., quenching) rates. 33,34 We develop an analytical model for the various quenching pathways, which matches our experimental results and can predict the emission dynamics and efficiencies for NCs of different (quasi-)spherical core–shell geometries and dopant concentrations.…”

Inorganic Phosphor Materials for Lighting

“…4f 7 and 5d 1 ? 4f 1 , respectively) with radiative decay times of the order of 1 ls for the former [93], and some tens of nanoseconds for the latter [94]. The 5d-4f transitions are allowed through the electric dipole mechanism and, therefore, are generally very strong.…”

Photonic Effects for Magnetic Dipole Transitions

“…As shown previously, doped NCs serve as ideal probes for photonic effects. 11,12,17−21 The size of NCs is well below the hundreds of nanometers over which photonic effects influence transitions for emitters inside NCs. The local coordination of emitters is fixed in the nanocrystalline host and is the same as in bulk material.…”

“…Oleate ligands on the surface allow the NCs to colloidally stabilize in apolar solvents with different n to investigate the influence of the photonic environment. 11,12 Six commonly used solvents are diethyl ether ( n = 1.35), hexane ( n = 1.38), octane ( n = 1.40), chloroform ( n = 1.45), toluene ( n = 1.50), and chlorobenzene ( n = 1.53). Figure 1c presents emission spectra for Eu 3+ -doped core and core–shell NCs for 5 D 2 excitation.…”