Engineering of the band gap and optical properties of thin films of yttrium hydride

You, Chang Chuan; Mongstad, Trygve; Mæhlen, Jan Petter; Karazhanov, Smagul

doi:10.1063/1.4891175

Cited by 45 publications

(52 citation statements)

References 16 publications

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“…However, it is important to remark that the optical model achieved by using Urbach and Cauchy functions is only valid in the long‐wavelength side of the band gap absorption, i.e., where k is expected to decrease following an exponential tail (in our case λ > 400 nm). For this reason, instead of using the ellipsometric model, the band gap calculations have been performed by using the experimental values of T , R , and considering a direct allowed transition, as described by C. You et al. The bigger band gap (3.6 eV) was found in the thinner film, S3, in agreement with our previous studies .…”

Section: Resultssupporting

confidence: 76%

“…For this reason, instead of using the ellipsometric model, the band gap calculations have been performed by using the experimental values of T , R , and considering a direct allowed transition, as described by C. You et al. The bigger band gap (3.6 eV) was found in the thinner film, S3, in agreement with our previous studies . The band gap of films S4 and S5 was found to be 3.4 and 2.8 eV, respectively.…”

Section: Resultssupporting

confidence: 74%

“…Oxygen‐containing yttrium hydride, from now referred in the text simply as YH x :O y , is an inorganic photochromic material reported for the first time in 2011 by Mongstad et al. YH x :O y is a positive and T ‐ type photochromic material, i.e., it darkens upon illumination and it recovers thermally back to the clear state once the illumination has ceased . YH x :O y responds to UVA or blue light and presents high transparency in the clear state, therefore it has multitude of potential applications including smart windows, ophthalmic lenses, security markings, and many more .…”

Section: Introductionmentioning

confidence: 99%

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Spectroscopic Ellipsometry and Microstructure Characterization of Photochromic Oxygen‐Containing Yttrium Hydride Thin Films

Montero

Karazhanov

2018

Physica Status Solidi (a)

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Oxygen‐containing yttrium hydride, YHx:Oy, is an inorganic phothochromic material which exhibits promising features for its application in smart windows, ophthalmic lenses, and many more. In the present work the optical properties of photochromic and non‐photochromic YHx:Oy thin films prepared by magnetron sputtering are studied by variable angle ellipsometry and spectrophotometry. These include the study of the complex refractive index, the transmittance, and luminous transmittance, as well as the reflectance of a selection of samples of diverse structural properties obtained under different deposition conditions. In the case of the photochromic YHx:Oy thin films, the refractive index in the near infrared and visible regions is found similar to the one corresponding to yttrium oxide, Y2O3. However, the YHx:Oy films exhibit a smaller band gap and hence higher absorption in the near ultraviolet than Y2O3. The photodarkening potential of the films are also quantified and characterized by the study and modeling of their optical properties before and after illumination. Our results show that photochromic YHx:Oy films, with a luminous transmittance above 80 % in the clear state, can reduce its transparency up to a 30% after 1 h illumination at 1 Sun.

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Section: Resultssupporting

confidence: 76%

Section: Resultssupporting

confidence: 74%

Section: Introductionmentioning

confidence: 99%

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Spectroscopic Ellipsometry and Microstructure Characterization of Photochromic Oxygen‐Containing Yttrium Hydride Thin Films

Montero

Karazhanov

2018

Physica Status Solidi (a)

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“…Recently, photo‐induced switching of optical properties has been observed in yttrium hydride (YH x ) films illuminated by visible laser light at pressures of several GPa at room temperature . Such effect was observed by Mongstad et al in oxidized YH x ; since then, YHO has attracted more and more research interest due to its high transparency in the clear state and its ability to photodarken evenly across the visible spectrum. YHO has promising applications in many fields such as ophthalmology, building and transportation industry, etc.…”

Section: Introductionmentioning

confidence: 98%

“…To date, many interesting properties and phenomena have been reported in YHO resulted by oxidation of the films: photochromic effect, optical bandgap engineering, the enhancement of oxygen concentration in the films with the increase of the hydrogen deposition pressure, etc. Mechanism of the photochromic effect in YHO has been suggested to be caused by formation, after intense illumination with blue/UV light, of small metallic domains within the YHO lattice .…”

Section: Introductionmentioning

confidence: 99%

Photoluminescence Properties of Photochromic Yttrium Hydride Films Containing Oxygen

Montero

Galeckas

Karazhanov

2018

Physica Status Solidi (b)

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Oxidation of YH xAEδ modulates its optical properties by converting it from optically opaque to transparent state to the visible light and electrical properties from metallic conductivity to insulating. The qualitative change of the materials properties are related to oxidation-induced modulation of electronic properties of the material that will influence the band gap and luminescence properties of the oxygen-containing yttrium hydride (YHO). This work presents the optical properties, studied by optical spectrophotometry and photoluminescence spectroscopy, of YHO thin films deposited by reactive magnetron sputtering at different H 2 /Ar flow ratios between 0.18 and 0.28. The indirect and direct band gap of the YHO photochromic films in their clear state is estimated from optical absorption measurements performed at room temperature, and found in the range between 2.5 and 2.6 eV (indirect allowed transition) and between 3.0 and 3.3 eV (direct allowed transition). The study of photoluminescence (PL) properties is performed in the temperature range between 10 and 300 K. The luminescence yield corresponding to the clear state was found to be extremely low in all the YHO films, and it reduced even further once the films darkened under UV-light exposure. The PL emission at room temperature covers the entire UV and visible range, comprising two broad bands centered at around 2.2 and 3.1 eV. The latter band became fine-structured at low-temperatures (10 K), showing a series of distinct PL peaks at energy positions between 2.8 and 3.4 eV which were independent of the H 2 /Ar flow ratio used during deposition. By the comparison of the PL measurements conducted in vacuum with the ones performed in air, it is possible to conclude that the environment plays an important role in the photochromic properties of YHO. The possible intrinsic and extrinsic origin of the structured PL emission is discussed in terms of excitonic features and/or luminescent surface defects. We report that the main optical transitions of the films deposited at different H pressures did not change by variation of temperature or by UV light-induced color change.

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Large Polaron Conduction, Photoconductivity, and Photochromism in GdO_xH₃_−2x Oxyhydride Thin Films

Colombi

Boshuizen

Chaykina

et al. 2023

Advanced Optical Materials

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At ambient conditions, rare‐earth oxyhydride thin films show reversible photochromism and photoconductivity, while their mechanism and relation are still unclear. In this work, this question is explored with in situ time‐resolved measurements of both optical and transport properties of Gd‐based oxyhydride thin films. It is found that p‐type large polaron conduction is the initial mechanism of charge transport; however, upon photo‐darkening, a 104‐fold increase of conductivity occurs, and n‐type carriers become dominant. Further, photochromism and photoconductivity are shown to originate from a single process, as indicated by the fact that the photoconductivity is exponentially proportional to the increase of optical absorption. This exponential relation, notably, cannot stem from any of the optically absorbing species thought responsible for photochromism and, therefore, suggests that their formation is accompanied by a concerted increase of negative charge carriers in the Gd oxyhydride films.

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Engineering of the band gap and optical properties of thin films of yttrium hydride

Cited by 45 publications

References 16 publications

Spectroscopic Ellipsometry and Microstructure Characterization of Photochromic Oxygen‐Containing Yttrium Hydride Thin Films

Spectroscopic Ellipsometry and Microstructure Characterization of Photochromic Oxygen‐Containing Yttrium Hydride Thin Films

Photoluminescence Properties of Photochromic Yttrium Hydride Films Containing Oxygen

Large Polaron Conduction, Photoconductivity, and Photochromism in GdO_xH₃_−2x Oxyhydride Thin Films

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Engineering of the band gap and optical properties of thin films of yttrium hydride

Cited by 45 publications

References 16 publications

Spectroscopic Ellipsometry and Microstructure Characterization of Photochromic Oxygen‐Containing Yttrium Hydride Thin Films

Spectroscopic Ellipsometry and Microstructure Characterization of Photochromic Oxygen‐Containing Yttrium Hydride Thin Films

Photoluminescence Properties of Photochromic Yttrium Hydride Films Containing Oxygen

Large Polaron Conduction, Photoconductivity, and Photochromism in GdOxH3−2x Oxyhydride Thin Films

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Large Polaron Conduction, Photoconductivity, and Photochromism in GdO_xH₃_−2x Oxyhydride Thin Films