How can I increase the range of an infrared emitter?
Some parameters that will affect your component selection:


Do you have other sources of interference (e.g. fluorescent lights)?
Power requirements?
What is the range that you'd like to get?
Are you transmitting data, or just detecting the presence/absence of an object?
Indoor/Outdoor use?


From General Overview of IR Transmission in Free Ambient:
"The maximum possible transmission distance of an IR
remote control system depends on various parameters, but
is mainly conditional on the radiant intensity of the emitter
(Ie) and the sensitivity of the receiver (Eemin.). Additionally,
the reflective conditions of the test room, the optical
transmittance of windows or light guides in front of the
receiver and the disturbance conditions influence the
maximum distance obtainable. "

Should be possible to calculate the theoretical maximum range of your receiver pair using Ee_min (sensitivity of receiver) and Ie (radiant intensity of emitter), where d = sqrt(Ie / Ee_min).

Fixed Gain - Interrupter/Light Curtain

This Vishay product brief suggests that there exist sensors that are "fixed gain type (AGC 0) with a fast 300 µs reaction time in light curtain and perimeter guard applications up to 30 meters".

It sounds like a fixed-gain IR receiver, with an appropriately matched transmitter, might be able to get you what you want, if you want object detection.  Are you looking for communication over IR, or simply object detection via IR?