Core-shell Layer for Room Temperature Infrared Sensing

Abstract

An infrared up-conversion device for converting LWIR radiation to NIR radiation includes a distribution of core-shell nano-sized particles within a transparent binder material. The core-shell particles can be composed of a HgTe core and a CdTe shell. The up-conversion device can be used with a NIR imager to function as an LWIR imager without the need for cryogenic cooling.

Claims

1. An infrared up-conversion device, comprising: a distribution of core-shell nanoparticles within a transparent binder material.

2. The device according to claim 1, wherein each of the core-shell nanoparticles is composed of a HgTe core and a CdTe shell.

3. The device according to claim 2, wherein the core has a 2-3 nm diameter and the shell has a 2-3 nm thickness.

4. The device according to claim 1, wherein the core has a 2-3 nm diameter and the shell has a 2-3 nm thickness.

5. An IR imager comprising: an infrared up-conversion device; and a near infrared imager coupled to the infrared up-conversion device; and the infrared up-conversion device comprising a distribution of core-shell nanoparticles within a transparent binder material.

6. The IR imager according to claim 5, wherein each of the core-shell nanoparticles is composed of a HgTe core and a CdTe shell.

7. The IR imager according to claim 6, wherein the core has a 2-3 nm diameter and the shell has a 2-3 nm thickness.

8. The IR imager according to claim 5, wherein the core has a 2-3 nm diameter and the shell has a 2-3 nm thickness.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a schematic cross-section of a focal plane array incorporating an exemplary embodiment of the invention;

[0015] FIG. 2 is a schematic sectional view of a nano particle taken from FIG. 1;

[0016] FIG. 3 is a schematic diagram of a bandgap of the core and shell;

[0017] FIG. 4 is a schematic diagram of an up-conversion system according to the exemplary embodiment of the invention; and

[0018] FIG. 5 is a schematic diagram of a system incorporating the exemplary embodiment of the invention.

DETAILED DESCRIPTION

[0019] While this invention is susceptible of embodiment in many different forms, there are shown in the drawings, and will be described herein in detail, specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated.

[0020] FIG. 1 is a schematic cross-section of a focal plane array incorporating an exemplary embodiment of the invention. Illustrated is a stack of layers forming an MIR imaging device 20. The device 20 includes an up-conversion layer 24 coupled to, such as by overlaying on, a NIR imager 28. The up-conversion layer 24 converts LWIR radiation to NIR radiation. The NIR imager 28 includes a semiconductor substrate 30 having NIR imaging elements 34 and a read out integrated circuit (ROIC) 36. ROIC structures are described in U.S. Pat. Nos. 6,657,194 and 5,581,084, herein incorporated by reference to the extent they are not contrary to the present disclosure.

[0021] The up-conversion layer 24 includes a transparent binder 38 having core-shell nanoparticles 44 disbursed and embedded therein.

[0022] FIG. 2 is a schematic sectional view of a nanoparticle 44 taken from FIG. 1. The particles 44 each comprise a core-shell structure. Each particle 44 can be composed of a spherical core 48 surrounded by a spherical shell 50. The core can be composed of HgTe and the shell can be composed of CdTe. The diameter of the core can be 2-3 nm HgTe with a bandgap of 1.3 eV (or 954 nm) due to quantum confinement and the shell made of 2-3 nm layer thick CdTe with a bulk bandgap of 1.5 eV (or 827 nm). The transparent binder 38 can comprise a polymer with a bandgap larger than 1.5 eV.

[0023] FIG. 3 is a schematic diagram of the bandgap the core and shell. The core can have a bandgap A eV wherein A can be 1.3, and the shell can have a bandgap of B eV, wherein B can be 1.5. The conduction band 40 and valence band 42 of the core and shell are offset by C eV, wherein C can be 0.1.

[0024] FIG. 4 is a schematic diagram of an up-conversion system according to the exemplary embodiment of the invention. A pump 60 with photon wavelength of 954 nm creates electron-hole pairs in the core 48 which are then moved to the shell 50 by a long wave infrared (LWIR) radiation signal 66. These e-h pairs in shell 48 recombine to emit a shorter wavelength (827 nm) radiation output 68 which will be used in the near infrared imager 28 at room temperature.

[0025] FIG. 5 is a schematic diagram of a system incorporating the exemplary embodiment of the invention. A conventional optics subsystem 80 and iris 84 gather and focus LWIR radiation 88 from a selected field-of-view. The IR radiation may be passed through a wavelength selective filter (not shown) before impacting a focal plane array (FPA) 90, configured according to FIG. 1. The pump 60, being an optical pumping source, provides optical pumping energy to FPA 90. The IR radiation impacting FPA 90 is converted (and optionally amplified) from LWIR wavelengths to NIR wavelengths by the up-conversion layer 24 using the optical energy provided by pump 60. The resulting NIR emissions are imaged using the ROIC 36. The ROIC 36 can be a conventional CMOS imaging circuit, a charge coupled device (CCD) imager, a two-dimensional array of silicon photodiodes or photo-conductors, or a silicon readout chip.

[0026] NIR image signals from FPA 90 are subsequently passed to amplifier(s) 114, analog-to-digital converter(s) 116, and a digital processor 118. A conventional RS video signal, for example, may be readily derived as an output signal from this IR imaging system. As needed, a conventional array address generator and array bias circuit (not shown) may be incorporated within the IR imaging system of FIG. 5.

[0027] From the foregoing, it will be observed that numerous variations and modifications may be utilized without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred.