InP based quantum dots (QDs) are coming in a big way as an alternative to toxic Cd, or Pb based QDs. Unlike many literature reports in this work, green-yellow-orange-red emitting highly photoluminescent (PLQY as high as 65%) and photostable InP/ZnSeS core/alloy shell quantum dots (CAS QDs) have been synthesized using a less toxic, air-stable aminophosphine precursor (P­(DMA)3). Unlike literature predictions in this paper, we show that green-yellow-orange-red emitting InP based alloyed QDs can be prepared with InCl3 only. We report here the hitherto unobserved and quite interesting excitation wavelength dependent PLQY for all of these green-yellow-orange-red emitting InP based CAS QDs. PLQY increases monotonically with increasing excitation wavelength. Significant deviation of the PL excitation spectrum from the absorption spectrum has been observed in the shorter wavelength region. This observation is perhaps because the surface mediated nonradiative pathways predominate over radiative charge carrier recombination when excited at shorter wavelength. PL decay for these QDs generally follows a triexponential decay equation with the shortest lifetime of 3–10 ns, the moderate one with a lifetime of 24–30 ns, and the longest one with a lifetime > 60 ns. Moderate and long lifetimes have been shown to be associated with two mutually interdependent excited-state decay channels, and the competition between these two decay channels dictates the PLQY of these CAS QDs. The moderate lifetime has been shown to be associated with an electron–hole recombination process, and the long lifetime is associated with delayed emission from the band edge due to interaction with the manifold of shallow traps. Quite interestingly, amplitude of the moderate lifetime (dynamical property) has been observed to be correlated with the PLQY (spectral property). PL decay for all of these InP based CAS QDs has been observed to be excitation wavelength independent. However, PL decay gets slower with increasing monitoring wavelength. Thus, the presence of shallow trap states is evidenced. Single particle blinking dynamics of InP based CAS QDs has been investigated for the first time. We could achieve the lowest reported magnitude of the m ON exponent for InP based QDs and the value is 1.19, which speaks about the much longer On-times or, in other words, superiority of our InP based CAS QD system in comparison to other reported InP based QDs, for example, InP core only, or InP/ZnS, InP/ZnSe/ZnS, InP/GaP/ZnS core/shell or core/shell/shell QD systems.

Highly luminescent (photoluminescence quantum yield (PLQY) as high as 96%) CdSe-based core/gradient alloy shell/shell (CGASS) quantum dots (QDs) have been synthesized in “one pot” using the reactivity difference between Cd and Zn precursors and Se and S precursors. This procedure is highly reproducible and quite useful for large-scale synthesis. Upon photoexcitation these QDs show a multiexponential excited state decay behavior. Interestingly, with the growth of the shell the overall PL decay gets faster. All the decay traces have been fitted well with a three exponential decay function. Fitted decay traces reveal three different time constants, a faster one of 1–4 ns, moderate one of 13–16 ns, and slower one >25 ns. With the growth of the shell, the amplitude for the moderate time constant increases, and that of the slow time constant decreases consistently. The variation of PLQY could be correlated with the variation of amplitude of the moderate time constant. Slow and moderate time constants have been shown to be associated with two mutually interdependent excited state decay channels, and the competition between these two decay channels dictates the PLQY of these CGASS QDs. The moderate time constant is associated with an electron–hole recombination process, and the slow time constant is associated with delayed emission from the band edge due to interaction with the manifold of shallow traps. The increase in magnitude of the amplitude of the moderate decay is reflected in higher PLQY. PL decay of blue-, green-, orange-, and red-emitting CGASS QDs follows a similar trend. This kind of uniform nature of PL decay of different color-emitting QDs is quite rare in the literature, and the fact that it has been observed in CGASS QDs perhaps hints toward the novelty of these systems. At the single-particle level these CGASS QDs are shown to be quite photostable without showing any blueing or bleaching for 1 h or even longer even under an air atmosphere. Thus, these CGASS QDs exhibit much improved optical behavior in comparison to CdSe/ZnS core/shell QDs. Quite interestingly all four differently emitting CGASS QDs optically behave in a similar way even at the single-particle level.

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Aim: The aim of this study was to carried out the audit of radiotherapy centers practicing conformal radiotherapy techniques and demonstrate the suitability of this indigenous optically stimulated luminescence (OSL) disc dosimeters in beam quality audit and verification of patient-specific dosimetry in conventional and conformal treatments in radiotherapy. Materials and Methods: Dose audit in conventional and conformal (intensity-modulated radiotherapy and volumetric-modulated arc therapy) radiotherapy techniques was conducted using in-house developed Al2O3:C-based OSL disc dosimeter and commercially available Gafchromic EBT3 film in 6 MV (flat and unflat) photon and 6 and 15 MeV electron beams. OSL disc dosimeter and Gafchromic EBT3 film measured dose values were verified using the ionization chamber measurements. Results: Percentage variations of doses measured by OSL disc dosimeters and EBT3 Gafchromic film for conventional radiotherapy technique were in the range of 0.15%–4.6% and 0.40%–5.45%, respectively, with respect to the treatment planning system calculated dose values. For conformal radiotherapy techniques, the percentage variations of OSL disc and EBT3 film measured doses were in the range of 0.1%–4.9% and 0.3%–5.0%, respectively. Conclusion: The results of this study supported by statistical evidence provided the confidence that indigenously developed Al2O3:C-based OSL disc dosimeters are suitable for dose audit in conventional and advanced radiotherapy techniques.