Amplified Spontaneous Emission and Optical Gain in Organic Single Crystal Quinquethiophene

Muhammad Zeb,Sawal Hamid Md Ali,Fazal Wahab,Muhammad Tahir,Mohd Faizul Mohd Sabri,Suhana Mohd Said,Mahidur R Sarker,Fida Muhammad

doi:10.3390/cryst9120609

Abstract

In this paper, we report optical characteristics of an organic single crystal oligomer 5,5⁗-diphenyl-2,2′:5′,2″:5″,2‴:5‴,2⁗-quinquethiophene (P5T). P5T crystal is a thiophene/phenylene co-oligomer that possesses better charge mobility as well as photoluminescence quantum efficiency (PLQE) as compared to other organic materials. Stimulated emission in P5T is investigated via amplified spontaneous emission (ASE) measurements within broad pump energies ranging from 35.26 to 163.34 µJ/cm2. An Nd-YAG femtosecond-tunable pulsed laser is used as a pump energy source for the ASE measurements of P5T crystals at an excitation wavelength of 445 nm. The ASE spectra exhibit optical amplification in P5T crystals at a 625 nm peak wavelength with a lower threshold energy density (Eth) ≈ 52.64 μJ/cm2. P5T also demonstrates higher optical gain with a value of 72 cm−1, that is calculated by using the variable stripe-length method. The value of PLQE is measured to be 68.24% for P5T. This study proposes potential applications of P5T single crystals in organic solid state lasers, photodetectors, and optical amplifiers.

Highlights

Organic semiconductors have received significant attention from researchers and scientists due to their potential applications in various electronic and optoelectronic devices such as organic light emitting diodes (OLEDs) [1,2,3], organic light emitting field effect transistors (OLEFETs) [4,5], organic photovoltaics (OPV) [6,7], and organic field effect transistors (OFETs) [8,9]
We study P5T crystal deposited on quartz glass (P5T/glass) as a wave-guide medium and for optical amplification through amplified spontaneous emission (ASE) measurements and optical gain characteristics
72 cm−1 which is much better than those measured for other organic materials, such as 22 cm−1 for narrowing, and the output intensity linearly increases with the excited stripe

Summary

Introduction

Organic semiconductors have received significant attention from researchers and scientists due to their potential applications in various electronic and optoelectronic devices such as organic light emitting diodes (OLEDs) [1,2,3], organic light emitting field effect transistors (OLEFETs) [4,5], organic photovoltaics (OPV) [6,7], and organic field effect transistors (OFETs) [8,9]. Thiophene/phenylene copolymers are made of thiophene and benzene rings in-line as backbone, which possesses higher charge mobility, is single-crystal in nature, and has high potential for optoelectronic devices [15,17]. Because of these extraordinary properties, thiophene/phenylene copolymers demonstrate spectrally narrow emissions, when optically pumped, and are the best candidates for OLEFETs [18]. The value of optical gain is calculated by the stripe-length method

Experimental Works

Results

Gain characteristics for waveguide

Conclusions