In recent years, quantum dots (QDs) have emerged as bright, color-tunable light sources for various applications such as light-emitting devices, lasing, and bioimaging. One important next step to advance their applicability is to reduce particle-toparticle variations of the emission properties as well as fluctuations of a single QD's emission spectrum, also known as spectral diffusion (SD). Characterizing SD is typically inefficient as it requires time-consuming measurements at the single-particle level.Here, however, we demonstrate multiparticle spectroscopy (MPS) as a high-throughput method to acquire statistically relevant information about both fluctuations at the single-particle level and variations at the level of a synthesis batch. In MPS, we simultaneously measure emission spectra of many (20−100) QDs with a high time resolution. We obtain statistics on single-particle emission line broadening for a batch of traditional CdSebased core−shell QDs and a batch of the less toxic InP-based core−shell QDs. The CdSe-based QDs show significantly narrower homogeneous line widths, less SD, and less inhomogeneous broadening than the InP-based QDs. The time scales of SD are longer in the InP-based QDs than in the CdSe-based QDs. Based on the distributions and correlations in single-particle properties, we discuss the possible origins of line-width broadening of the two types of QDs. Our experiments pave the way to large-scale, high-throughput characterization of single-QD emission properties and will ultimately contribute to facilitating rational design of future QD structures.

This does not only create a warmer white color but also generally raises the color rendering index, thereby making the color of the lamp more pleasant to the human eye. [5] However, it comes with the downside of decreased luminous efficacy due to emission at wavelengths where the eye is less sensitive. [6] An alternative class of red-emitting materials with higher luminous efficacy than CASN:Eu 2+ , is the Mn 4+ -doped fluorides. [7][8][9] These materials have absorption bands in the ultraviolet (UV) and blue due to spin-allowed transitions. Their roomtemperature wet-chemical synthesis is relatively simple and the narrow emission lines around 630 nm give rise to a red color with a high luminous efficacy. [10,11] These properties make Mn 4+ -doped fluorides excellent blue-to-red converting phosphors for low-power applications such as displays. However, for lighting applications where the light powers are generally orders of magnitude higher, the use of Mn 4+ -doped fluorides is complicated by droop: at increasing blue illumination powers, the output of the phosphor increases sub-linearly, approaches a maximum, and may eventually even drop. [12][13][14] These phenomena can occur already at excitation densities of 100 W cm −2 that are typical in (home) lighting w-LEDs and negatively affect the energy efficiency and the perceived color of Mn 4+ -containing w-LEDs. [15] The origin of luminescence droop of Mn 4+ -doped fluorides is not entirely clear and various mechanisms have been proposed. For example, Mn 4+ -doped fluorides are known to suffer from temperature quenching above temperatures of 400-500 K. [16] Illumination-induced heating may hence lead to an efficiency drop at high excitation powers. [17] In addition, the long 5-10 ms lifetime of the 2 E excited state of Mn 4+ could contribute to droop as it results in a high steady-state population of excited Mn 4+ ions. Excited Mn 4+ ions bleach the 4 A 2 → 4 T 2 absorption, which ultimately limits the photon conversion rate per Mn 4+ dopant to an amount equal to the inverse of the lifetime. More indirectly, the high steady-state population of excited Mn 4+ at high excitation powers may lead to additional losses through excited-state absorption of the blue excitation light or through Auger energy transfer. [18] These losses could be remedied in part by gentle illumination-induced heating up to 400 K because the radiative lifetime and, hence, the steady-state 2 E excited state population decrease with temperature without the loss of light output. [19] Mn 4+ -doped fluorides are popular phosphors for warm-white lighting, converting blue light from light-emitting diodes (LEDs) into red light. However, they suffer from droop, that is, decreasing performance at increasing power, limiting their applicability for high-power applications. Previous studies highlight different causes of droop. Here, a unified picture of droop of Mn 4+doped K 2 TiF 6 , accounting for all previously proposed mechanisms, is provided. Combining continuous-wave and pulsed experiments on samples o...