Quantum Dot Liquid Scintillators T. Wongjirad (MIT) for A. Elagin - PowerPoint PPT Presentation

Quantum Dot Liquid Scintillators T. Wongjirad (MIT) for A. Elagin (U. Chicago), D. Gooding (MIT), 
 B. Naranjo (UCLA), J. Ouellet (MIT), R. Schofield (UCLA), L. Winslow (MIT) FroST, 3/16/2016 1 photo: plasmachem

Introduction Outline • Quantum dot nanocrystal are an intriguing material for the use in scintillator experiments • Controllable optical properties • Can be suspended in both water and organic scintillator • Made out of elements that can be used in neutrino-less double beta decay searches FroST 2016 T. Wongjirad (MIT) 2

Introduction Outline • What are quantum dot nanocrystals? • Past and current work on quantum dot liquid scintillators (QD LS) • NuDot — a prototype directional liquid scintillator detector for R&D on LS such as including a QD LS FroST 2016 T. Wongjirad (MIT) 3 3

Quantum Dots Outline • Quantum dots are nanometer-scale crystals of semi-conductor with interesting optical properties • They are suspended in both organic solvents and water through the use of surface coordinating ligands • These ligands are also 
 critical in the synthesis of the QDs FroST 2016 T. Wongjirad (MIT) 4 4

Growing Quantum Dots Outline capping ligand • QDs made by Cd Inject TOPSe into growing crystals in hot (225⁰C) MeCd solution solution • Start by mixing metal components and capping ligands capping ligand MeCd + TOPSe → CdSe + monomers FroST 2016 T. Wongjirad (MIT) 5 5

Growing Quantum Dots Outline • Metals nucleate and begin forming Cd a crystal • Capping ligands coordinate on the surface, controlling the reaction rate, preventing agglomeration, and keeping the crystal MeCd + TOPSe → CdSe + monomers in suspension FroST 2016 T. Wongjirad (MIT) 6 6

QDs made of 0 νββ Isotopes Outline • Elements used to make QDs are also elements Isotope Endpoint Abundance with which to look for neutrino-less double 48 Ca 4.271 MeV 0.187% beta decay 150 Nd 3.367 MeV 5.6% • QD Examples: 96 Zr 3.350 MeV 2.8% • CdSe/ZnS 100 Mo 3.034 MeV 9.6% • CdTe 82 Se 2.995 MeV 9.2% • Nd 2 O 3 116 Cd 2.802 MeV 7.5% 130 Te 2.533 MeV 34.5% • ZrO 136 Xe 2.479 MeV 8.9% • QDs are a way to load 76 Ge 2.039 MeV 7.8% scintillator, but also come with great optical 128 Te 0.868 MeV 31.7% properties that we can take advantage of! FroST 2016 T. Wongjirad (MIT) 7 7

Optical Properties Outline • Like bulk semiconductor, QDs can absorb/emit photons through the creation/ annihilation of an exciton • But because crystals are small, the exciton’s wave function is confined - similar to a particle in a box • confinement separates energy levels and widens band gap (compared to bulk crystal) FroST 2016 T. Wongjirad (MIT) 8 8

Optical Properties Outline • result: QDs absorb broadly in the UV and emit in a narrow band of wavelengths blue curve: absorption red curve: emission FroST 2016 T. Wongjirad (MIT) 9 9

Optical Properties Outline • Furthermore, because of the confinement effect, the color emitted is directly dependent on the size of the QD FroST 2016 T. Wongjirad (MIT) 10 10

Optical Properties Outline • The size to which they grow can be controlled • Can make the QDs duration that best fit your of synthesis goals! time FroST 2016 T. Wongjirad (MIT) 11 11

QD Uses Outline • QDs are used in • Biological labeling • Improved solar cells • TVs • Admittedly, QDs are still expensive ($100 to $10K per gram), but with commercial uses, there is hope that production increases and prices goes down FroST 2016 T. Wongjirad (MIT) 12 12

QDs for Detectors Outline • How do QDs help scintillators (apart from loading metal)? • One way is that it could help in the gathering of directional information in large-scale scintillator detectors FroST 2016 T. Wongjirad (MIT) 13 13

Directional Information Outline • Cherenkov Number of Cherenkov Photons for a 1MeV e- photons provide absorbed by scintillator info on direction of particles that can be used to separate signal and background • However, only long wavelengths can avoid absorption by the scintillator JINST 7 (2012) P07010 FroST 2016 T. Wongjirad (MIT) 14 14

Directional Information Outline • Still, there is Number of Cherenkov Photons for a 1MeV e- some region absorbed by scintillator where Cherenkov photons can escape and still be detected JINST 7 (2012) P07010 FroST 2016 T. Wongjirad (MIT) 15 15

(DC T arget) normalized at peak to KamLAND emission.dat normalized and shifted by 80nm KamLAND (emission.dat) Directional Information Outline • Quantum Dots have a tunable absorption and emission spectra • Want a narrow emission spectra and absorption spectra that ends at low wavelengths allowing more long-wavelength Cherenkov photons to pass 140 KamLAND emission spectrum QD Cytodiagnostics spectrum (peak at 461nm) 120 same as red, shifted by -77nm emission [a.u.] 100 80 60 40 20 0 200 300 400 500 600 700 wavelength [nm] FroST 2016 T. Wongjirad (MIT) 16 16

Directional Information Outline • With fast enough electronics, one could identify Cherenkov from Scintillation photons assuming 0.1 ns resolution black: Cherenkov photons red: scintillation photons R c/s = 0.86 JINST 9 (2014) P06012 FroST 2016 T. Wongjirad (MIT) 17 17

Work in Progress Outline Work is being done to explore using directionality and • QDs in LS. Past published results can be found here: JINST 7 (2012) P07010 arXiv:1202.4733 JINST 8 (2013) P10015 arXiv:1307.4742 JINST 9 (2014) P06012 arXiv:1307.5813 Some quick highlights • FroST 2016 T. Wongjirad (MIT) 18 18

Past Measurements Outline Demonstrated QDs act as tertiary wavelength shifter • 150,000 120,000 CdS400 100,000 addition of PPO emission [a.u.] emission [a.u.] CdS400 + 5g/l PPO Trilite450 T oluene + 5g/l PPO Trilite450 + 5g/l PPO 100,000 as intermediate 80,000 T oluene + 5g/l PPO wavelength-shifter 60,000 helps light yield 50,000 40,000 20,000 0 0 350 400 450 500 550 600 650 350 400 450 500 550 600 650 wavelength [nm] wavelength [nm] JINST 8 (2013) P10015 arXiv:1307.4742 FroST 2016 T. Wongjirad (MIT) 19 19

Past Measurements Outline Emission spectra varies on type of dots and who made • them — we want as narrow as possible state-of-the-art are core/shell QDs with high quantum yield • and smaller long wavelength emission tail (QYs > 0.7) 4e+06 CdS400 (exc. at 360 nm) Trilite450 (exc. at 425 nm) CdS380 S1 (exc. at 360 nm) emission [a.u.] CdS380 S1 (exc. at 360 nm) 3e+06 with Fluoromax 3 Trilite is a core/shell QD Rest are core-only 2e+06 1e+06 Shell of different semi-conductor elements 0 shields core’s surface 400 500 600 700 and improves stability, QY wavelength [nm] JINST 8 (2013) P10015 arXiv:1307.4742 FroST 2016 T. Wongjirad (MIT) 20 20

Past Measurements 2 Outline 2 • Absorbance tail at long wavelengths can grow over time — but can be cleaned up via filtering CdS380 S1 (March 13, 2013) 0.15 CdS380 S1 (March 25, 2013) 0.6 CdS380 S1 (June 11, 2013) CdS380 S1 (June 18, 2013) absorbance CdS380 S1 (June 18, 2013) filtered absorbance CdS380 S1 (June 18, 2013) CdS380 S2 (June 11, 2013) 0.1 CdS380 S1 (June 18, 2013) filtered 0.4 L = 0.54 m 0.05 0.2 L = 1.08 m 0 0 400 500 600 700 800 400 500 600 700 wavelength [nm] wavelength [nm] FroST 2016 T. Wongjirad (MIT) 21 21

The overlap of the the absorption spectrum of quantum dots and the emission spectrum of quantum dots in toluene doped with 2.0 Current Measurements [g/L] of PPO. (Left) Outline • Avoiding overlap between the absorbance and emission spectra is important in maximizing light yield The area of the overlap vs light yield of the quantum dots. (Above) (this and other studies in preparation for publication) FroST 2016 T. Wongjirad (MIT) 22 22

Further R&D Outline • Many open questions still. Some examples: • What is the absolute light yield for a sizable detector? • What is the absorption and scattering lengths at different wavelengths? • Will new types of QDs improve the above? • How to work with QD LS (e.g. purification)? FroST 2016 T. Wongjirad (MIT) 23 23

Synthesis Outline We’re starting to learn how synthesize our own dots in order to have samples for testing Diana Gooding, trained chemist turned physicist Our first batch of QDs FroST 2016 T. Wongjirad (MIT) 24 24

BG Rejection using Topology Outline of Cherenkov/Scintillation Photons two-tracks (double-beta decay signal) vs single-track (8B solar neutrino background) Single 2.53 MeV electron Cherenkov PEs Scintillation PEs Differences that are hardly seen by eye can be reconstructed by pattern recognition e.g. spherical harmonics analysis Simulation details l 6.5m radius detector, scintillator model from KamLAND simulation l TTS=100 ps, 100% area coverage, QE 12-23% Power spectrum l Light within a pre-defined time window to capture early light (rotation invariant: works well in Key parameters determining separation of 0 νββ -decay from 8 B: spherical geometry e.g., SNO+, KamLAND ) l Scintillator properties (narrow spectrum, slow rise time) l Photo-detector properties (fast, large-area, high QE) (Publication in preparation) FroST 2016 T. Wongjirad (MIT) 25 25

Further R&D Outline NuDot: A Prototype Directional Liquid Scintillator FroST 2016 T. Wongjirad (MIT) 26 26