Elsevier

Materials Chemistry and Physics

Volume 163, 1 August 2015, Pages 554-561
Materials Chemistry and Physics

Structural and optical properties of ZnSe quantum dots in glass nanocomposites

https://doi.org/10.1016/j.matchemphys.2015.08.013Get rights and content

Highlights

  • ZnSe quantum dots embedded glass-nanocomposites were synthesized.

  • Nanocrystal sizes were controlled by the heat treatment schedule.

  • Structure and optical properties of nano-sized ZnSe in glass were investigated.

  • Strong visible red photoluminescence was obtained from these nanocomposites.

Abstract

Zinc selenide (ZnSe) quantum dots (QDs) were synthesized in a dielectric (borosilicate glass) matrix for the first time by melt-quenching process followed by thermal treatment. Sizes of the quantum dots were varied by post thermal treatment. UV–Vis optical absorption spectroscopy, transmission electron microscopy (TEM) and Raman spectroscopy were deployed to investigate the ZnSe QDs. TEM analysis reveals QD sizes of the order of 2–4 nm and relatively larger nanocrystals having sizes of the order of 15–26 nm. The sizes of the QDs have also been verified with the help of effective mass approximation model and optical absorption spectroscopy. The quantum confinement effect has been observed for both variation of heat treatment temperature and time. The Raman spectra of the nanocomposites reveal blue-shifted Raman peaks of ZnSe at 295 and 315 cm−1 due to phonon confinement effect. The decrease in Raman intensity with heat treatment indicates increase in size of the QDs. Red luminescence from the ZnSe-glass nanocomposites peaking at 708 nm due to the size related as well as traps related states makes their applications towards luminescent solar concentrators (LSCs).

Introduction

Nanostructured materials exhibit interesting novel properties that are surprisingly different from their bulk properties. The sizes of the nanomaterials offer the opportunity to control these properties, mainly their optical properties. Particularly, the II–VI semiconductors (ZnS, ZnSe, CdS, CdSe, etc.) show maximum response to the size related properties within 1–100 nm size range. Semiconductor nanocrystals (NCs) having sizes comparable to the exciton Bohr radius shows three dimensional quantum confinement effect. These semiconductor NCs having such small dimensions are called the quantum dots (QDs). These QDs modify the optical properties like optical absorption, photoluminescence (PL) and the nonlinear refractive index towards the application field of optical communication and optical limiters [1], [2]. Again their wide band gap values, high quantum efficiency and availability in multiple colors (based on their sizes) make themselves as a replacement to the traditional phosphors in many areas such as solid-state lighting devices, luminescent materials, and biological applications [3], [4]. So, the optical properties of these II–VI semiconductor nanoparticles have been the most investigated topic in this recent decade apart from their other usages in memory element devices [5] and applications towards second harmonic generations [6].

Zinc selenide (ZnSe) is the less investigated material compared to the other II–VI compound semiconductors such as ZnS, CdS, CdSe, etc. even though it is an important semiconductor material with a wide band gap (∼2.70 eV). High-performance blue/ultraviolet-light-sensitive ZnSe-nanobelts have been investigated and details can be found in published literature [7]. ZnSe has been used in II–VI light-emitting diodes (LEDs) and diode lasers working in the blue-light region as they are much sensitive to UV/blue light. Synthesis of ZnSe NCs in glass matrix and their luminescence at two photon absorption, second harmonic generation has been reported in the literature [8]. Colloidal ZnSe NCs having PL in the spectral range 390–440 nm has also been investigated [9]. Photoelectric properties of ZnSe nanostructures have also been reported by Philipose et al. [10].

Multiple physical and chemical methods have been used to synthesize II–VI semiconductor nanostructures. Some physical process such as molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD) approaches are taken to form quantum dots [11], [12] and vapor–liquid–solid (VLS) approaches to form quantum wires [13], [14]. Besides these, synthesis of semiconductor NCs in glass matrix by sol–gel process has also been reported [15]. But the report on the synthesis of II–VI semiconductor NCs by the melt-quenching technique followed by thermal treatment is very few [16], [17], [18]. Again in the maximum cases, the commercial filter glasses have been taken as the precursor glasses for the study [19], [20]. So the synthesis and optical properties of ZnSe QDs embedded glass nanocomposites are particularly appealing.

In this paper, we report the synthesis of ZnSe QDs by a single step in-situ process in SiO2–Al2O3–Na2O–K2O–B2O3 system. The sizes of the NCs were controlled by varying the thermal treatment temperature and time. The optical properties were examined by studying the optical absorption spectra, Raman spectra and size of these NCs were estimated using the effective mass approximation model. The PL properties of the ZnSe nanostructured dielectric nanocomposites are also discussed.

Section snippets

Preparation of dielectric nanocomposites

In this work, ZnSe NCs are synthesized in a glass system with nominal composition of 49SiO2-3Al2O3-4Na2O-31K2O-13B2O3 (wt. %) and 0.6 wt.% ZnSe was added to the base glass. Quartz, SiO2 (Bremthaler/Quarzitwerk, Usingen, Germany), alumina, Al2O3 (99%; Aldrich, Milwaukee, Wisconsin), sodium carbonate, Na2CO3 (Anhydrous GR, Loba Chemie, India) potassium carbonate, K2CO3 (Anhydrous GR, Loba Chemie, India), boric acid, H3BO3 (99.5%; Fluka Chemika, Gmbh, Buchs, Germany) and zinc selenide, ZnSe

Density and thermal properties

The 0.6 wt.% ZnSe added precursor glass sample is designated as ZS-0h. The glass transition temperature (Tg), dilatometric deformation temperature (Td) and the coefficient of thermal expansion (CTE) of ZS-0h were determined by using a dilatometer. The value of Tg and Td were found to be 527 °C and 559 °C. CTE was determined over the temperature range 50–400 °C and found to be 12.2 × 10−06 K−1. The ZnSe added precursor glass was heat treated at 530, 540 and 550 °C for a constant duration (10 h)

Conclusions

ZnSe QDs have been synthesized in dielectric (borosilicate glass) matrix via simple melt-quench technique and followed by post thermal treatment. The sizes of the QDs are controlled by varying both thermal treatment temperatures and time. The thermal, optical and luminescence properties of ZnSe QDs embedded SiO2–Al2O3–Na2O–K2O–B2O3 system have been investigated. The absorption spectra of the nanocomposites reveal presence of two different ranges of ZnSe nanoparticle sizes. The sizes of the QDs

Acknowledgments

The authors thank Mr. Kamal Dasgupta, Acting Director and Dr. R. Sen, Head, Glass Division of CSIR-CGCRI for their encouragement to carry out this work. We gratefully acknowledge the financial support of BRNS/DAE under sanction no. 2011/34/6/BRNS. We gratefully acknowledge Dr. Goutam De and Mr. Manish Kumar Mishra, Nano Structured Materials Division of this institute for recording Raman Spectra of the samples. We also thankfully acknowledge the Electron Microscope Section of the institute for

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